Back to home page

LXR

 
 

    


0001 /*
0002  *  Generic process-grouping system.
0003  *
0004  *  Based originally on the cpuset system, extracted by Paul Menage
0005  *  Copyright (C) 2006 Google, Inc
0006  *
0007  *  Notifications support
0008  *  Copyright (C) 2009 Nokia Corporation
0009  *  Author: Kirill A. Shutemov
0010  *
0011  *  Copyright notices from the original cpuset code:
0012  *  --------------------------------------------------
0013  *  Copyright (C) 2003 BULL SA.
0014  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
0015  *
0016  *  Portions derived from Patrick Mochel's sysfs code.
0017  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
0018  *
0019  *  2003-10-10 Written by Simon Derr.
0020  *  2003-10-22 Updates by Stephen Hemminger.
0021  *  2004 May-July Rework by Paul Jackson.
0022  *  ---------------------------------------------------
0023  *
0024  *  This file is subject to the terms and conditions of the GNU General Public
0025  *  License.  See the file COPYING in the main directory of the Linux
0026  *  distribution for more details.
0027  */
0028 
0029 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0030 
0031 #include <linux/cgroup.h>
0032 #include <linux/cred.h>
0033 #include <linux/ctype.h>
0034 #include <linux/errno.h>
0035 #include <linux/init_task.h>
0036 #include <linux/kernel.h>
0037 #include <linux/list.h>
0038 #include <linux/magic.h>
0039 #include <linux/mm.h>
0040 #include <linux/mutex.h>
0041 #include <linux/mount.h>
0042 #include <linux/pagemap.h>
0043 #include <linux/proc_fs.h>
0044 #include <linux/rcupdate.h>
0045 #include <linux/sched.h>
0046 #include <linux/slab.h>
0047 #include <linux/spinlock.h>
0048 #include <linux/percpu-rwsem.h>
0049 #include <linux/string.h>
0050 #include <linux/sort.h>
0051 #include <linux/kmod.h>
0052 #include <linux/delayacct.h>
0053 #include <linux/cgroupstats.h>
0054 #include <linux/hashtable.h>
0055 #include <linux/pid_namespace.h>
0056 #include <linux/idr.h>
0057 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
0058 #include <linux/kthread.h>
0059 #include <linux/delay.h>
0060 #include <linux/atomic.h>
0061 #include <linux/cpuset.h>
0062 #include <linux/proc_ns.h>
0063 #include <linux/nsproxy.h>
0064 #include <linux/file.h>
0065 #include <net/sock.h>
0066 
0067 #define CREATE_TRACE_POINTS
0068 #include <trace/events/cgroup.h>
0069 
0070 /*
0071  * pidlists linger the following amount before being destroyed.  The goal
0072  * is avoiding frequent destruction in the middle of consecutive read calls
0073  * Expiring in the middle is a performance problem not a correctness one.
0074  * 1 sec should be enough.
0075  */
0076 #define CGROUP_PIDLIST_DESTROY_DELAY    HZ
0077 
0078 #define CGROUP_FILE_NAME_MAX        (MAX_CGROUP_TYPE_NAMELEN +  \
0079                      MAX_CFTYPE_NAME + 2)
0080 
0081 /*
0082  * cgroup_mutex is the master lock.  Any modification to cgroup or its
0083  * hierarchy must be performed while holding it.
0084  *
0085  * css_set_lock protects task->cgroups pointer, the list of css_set
0086  * objects, and the chain of tasks off each css_set.
0087  *
0088  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
0089  * cgroup.h can use them for lockdep annotations.
0090  */
0091 #ifdef CONFIG_PROVE_RCU
0092 DEFINE_MUTEX(cgroup_mutex);
0093 DEFINE_SPINLOCK(css_set_lock);
0094 EXPORT_SYMBOL_GPL(cgroup_mutex);
0095 EXPORT_SYMBOL_GPL(css_set_lock);
0096 #else
0097 static DEFINE_MUTEX(cgroup_mutex);
0098 static DEFINE_SPINLOCK(css_set_lock);
0099 #endif
0100 
0101 /*
0102  * Protects cgroup_idr and css_idr so that IDs can be released without
0103  * grabbing cgroup_mutex.
0104  */
0105 static DEFINE_SPINLOCK(cgroup_idr_lock);
0106 
0107 /*
0108  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
0109  * against file removal/re-creation across css hiding.
0110  */
0111 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
0112 
0113 /*
0114  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
0115  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
0116  */
0117 static DEFINE_SPINLOCK(release_agent_path_lock);
0118 
0119 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
0120 
0121 #define cgroup_assert_mutex_or_rcu_locked()             \
0122     RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&           \
0123                !lockdep_is_held(&cgroup_mutex),     \
0124                "cgroup_mutex or RCU read lock required");
0125 
0126 /*
0127  * cgroup destruction makes heavy use of work items and there can be a lot
0128  * of concurrent destructions.  Use a separate workqueue so that cgroup
0129  * destruction work items don't end up filling up max_active of system_wq
0130  * which may lead to deadlock.
0131  */
0132 static struct workqueue_struct *cgroup_destroy_wq;
0133 
0134 /*
0135  * pidlist destructions need to be flushed on cgroup destruction.  Use a
0136  * separate workqueue as flush domain.
0137  */
0138 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
0139 
0140 /* generate an array of cgroup subsystem pointers */
0141 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
0142 static struct cgroup_subsys *cgroup_subsys[] = {
0143 #include <linux/cgroup_subsys.h>
0144 };
0145 #undef SUBSYS
0146 
0147 /* array of cgroup subsystem names */
0148 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
0149 static const char *cgroup_subsys_name[] = {
0150 #include <linux/cgroup_subsys.h>
0151 };
0152 #undef SUBSYS
0153 
0154 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
0155 #define SUBSYS(_x)                              \
0156     DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);         \
0157     DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);          \
0158     EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);          \
0159     EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
0160 #include <linux/cgroup_subsys.h>
0161 #undef SUBSYS
0162 
0163 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
0164 static struct static_key_true *cgroup_subsys_enabled_key[] = {
0165 #include <linux/cgroup_subsys.h>
0166 };
0167 #undef SUBSYS
0168 
0169 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
0170 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
0171 #include <linux/cgroup_subsys.h>
0172 };
0173 #undef SUBSYS
0174 
0175 /*
0176  * The default hierarchy, reserved for the subsystems that are otherwise
0177  * unattached - it never has more than a single cgroup, and all tasks are
0178  * part of that cgroup.
0179  */
0180 struct cgroup_root cgrp_dfl_root;
0181 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
0182 
0183 /*
0184  * The default hierarchy always exists but is hidden until mounted for the
0185  * first time.  This is for backward compatibility.
0186  */
0187 static bool cgrp_dfl_visible;
0188 
0189 /* Controllers blocked by the commandline in v1 */
0190 static u16 cgroup_no_v1_mask;
0191 
0192 /* some controllers are not supported in the default hierarchy */
0193 static u16 cgrp_dfl_inhibit_ss_mask;
0194 
0195 /* some controllers are implicitly enabled on the default hierarchy */
0196 static unsigned long cgrp_dfl_implicit_ss_mask;
0197 
0198 /* The list of hierarchy roots */
0199 
0200 static LIST_HEAD(cgroup_roots);
0201 static int cgroup_root_count;
0202 
0203 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
0204 static DEFINE_IDR(cgroup_hierarchy_idr);
0205 
0206 /*
0207  * Assign a monotonically increasing serial number to csses.  It guarantees
0208  * cgroups with bigger numbers are newer than those with smaller numbers.
0209  * Also, as csses are always appended to the parent's ->children list, it
0210  * guarantees that sibling csses are always sorted in the ascending serial
0211  * number order on the list.  Protected by cgroup_mutex.
0212  */
0213 static u64 css_serial_nr_next = 1;
0214 
0215 /*
0216  * These bitmask flags indicate whether tasks in the fork and exit paths have
0217  * fork/exit handlers to call. This avoids us having to do extra work in the
0218  * fork/exit path to check which subsystems have fork/exit callbacks.
0219  */
0220 static u16 have_fork_callback __read_mostly;
0221 static u16 have_exit_callback __read_mostly;
0222 static u16 have_free_callback __read_mostly;
0223 
0224 /* cgroup namespace for init task */
0225 struct cgroup_namespace init_cgroup_ns = {
0226     .count      = { .counter = 2, },
0227     .user_ns    = &init_user_ns,
0228     .ns.ops     = &cgroupns_operations,
0229     .ns.inum    = PROC_CGROUP_INIT_INO,
0230     .root_cset  = &init_css_set,
0231 };
0232 
0233 /* Ditto for the can_fork callback. */
0234 static u16 have_canfork_callback __read_mostly;
0235 
0236 static struct file_system_type cgroup2_fs_type;
0237 static struct cftype cgroup_dfl_base_files[];
0238 static struct cftype cgroup_legacy_base_files[];
0239 
0240 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
0241 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
0242 static int cgroup_apply_control(struct cgroup *cgrp);
0243 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
0244 static void css_task_iter_advance(struct css_task_iter *it);
0245 static int cgroup_destroy_locked(struct cgroup *cgrp);
0246 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
0247                           struct cgroup_subsys *ss);
0248 static void css_release(struct percpu_ref *ref);
0249 static void kill_css(struct cgroup_subsys_state *css);
0250 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
0251                   struct cgroup *cgrp, struct cftype cfts[],
0252                   bool is_add);
0253 
0254 /**
0255  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
0256  * @ssid: subsys ID of interest
0257  *
0258  * cgroup_subsys_enabled() can only be used with literal subsys names which
0259  * is fine for individual subsystems but unsuitable for cgroup core.  This
0260  * is slower static_key_enabled() based test indexed by @ssid.
0261  */
0262 static bool cgroup_ssid_enabled(int ssid)
0263 {
0264     if (CGROUP_SUBSYS_COUNT == 0)
0265         return false;
0266 
0267     return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
0268 }
0269 
0270 static bool cgroup_ssid_no_v1(int ssid)
0271 {
0272     return cgroup_no_v1_mask & (1 << ssid);
0273 }
0274 
0275 /**
0276  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
0277  * @cgrp: the cgroup of interest
0278  *
0279  * The default hierarchy is the v2 interface of cgroup and this function
0280  * can be used to test whether a cgroup is on the default hierarchy for
0281  * cases where a subsystem should behave differnetly depending on the
0282  * interface version.
0283  *
0284  * The set of behaviors which change on the default hierarchy are still
0285  * being determined and the mount option is prefixed with __DEVEL__.
0286  *
0287  * List of changed behaviors:
0288  *
0289  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
0290  *   and "name" are disallowed.
0291  *
0292  * - When mounting an existing superblock, mount options should match.
0293  *
0294  * - Remount is disallowed.
0295  *
0296  * - rename(2) is disallowed.
0297  *
0298  * - "tasks" is removed.  Everything should be at process granularity.  Use
0299  *   "cgroup.procs" instead.
0300  *
0301  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
0302  *   recycled inbetween reads.
0303  *
0304  * - "release_agent" and "notify_on_release" are removed.  Replacement
0305  *   notification mechanism will be implemented.
0306  *
0307  * - "cgroup.clone_children" is removed.
0308  *
0309  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
0310  *   and its descendants contain no task; otherwise, 1.  The file also
0311  *   generates kernfs notification which can be monitored through poll and
0312  *   [di]notify when the value of the file changes.
0313  *
0314  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
0315  *   take masks of ancestors with non-empty cpus/mems, instead of being
0316  *   moved to an ancestor.
0317  *
0318  * - cpuset: a task can be moved into an empty cpuset, and again it takes
0319  *   masks of ancestors.
0320  *
0321  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
0322  *   is not created.
0323  *
0324  * - blkcg: blk-throttle becomes properly hierarchical.
0325  *
0326  * - debug: disallowed on the default hierarchy.
0327  */
0328 static bool cgroup_on_dfl(const struct cgroup *cgrp)
0329 {
0330     return cgrp->root == &cgrp_dfl_root;
0331 }
0332 
0333 /* IDR wrappers which synchronize using cgroup_idr_lock */
0334 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
0335                 gfp_t gfp_mask)
0336 {
0337     int ret;
0338 
0339     idr_preload(gfp_mask);
0340     spin_lock_bh(&cgroup_idr_lock);
0341     ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
0342     spin_unlock_bh(&cgroup_idr_lock);
0343     idr_preload_end();
0344     return ret;
0345 }
0346 
0347 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
0348 {
0349     void *ret;
0350 
0351     spin_lock_bh(&cgroup_idr_lock);
0352     ret = idr_replace(idr, ptr, id);
0353     spin_unlock_bh(&cgroup_idr_lock);
0354     return ret;
0355 }
0356 
0357 static void cgroup_idr_remove(struct idr *idr, int id)
0358 {
0359     spin_lock_bh(&cgroup_idr_lock);
0360     idr_remove(idr, id);
0361     spin_unlock_bh(&cgroup_idr_lock);
0362 }
0363 
0364 static struct cgroup *cgroup_parent(struct cgroup *cgrp)
0365 {
0366     struct cgroup_subsys_state *parent_css = cgrp->self.parent;
0367 
0368     if (parent_css)
0369         return container_of(parent_css, struct cgroup, self);
0370     return NULL;
0371 }
0372 
0373 /* subsystems visibly enabled on a cgroup */
0374 static u16 cgroup_control(struct cgroup *cgrp)
0375 {
0376     struct cgroup *parent = cgroup_parent(cgrp);
0377     u16 root_ss_mask = cgrp->root->subsys_mask;
0378 
0379     if (parent)
0380         return parent->subtree_control;
0381 
0382     if (cgroup_on_dfl(cgrp))
0383         root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
0384                   cgrp_dfl_implicit_ss_mask);
0385     return root_ss_mask;
0386 }
0387 
0388 /* subsystems enabled on a cgroup */
0389 static u16 cgroup_ss_mask(struct cgroup *cgrp)
0390 {
0391     struct cgroup *parent = cgroup_parent(cgrp);
0392 
0393     if (parent)
0394         return parent->subtree_ss_mask;
0395 
0396     return cgrp->root->subsys_mask;
0397 }
0398 
0399 /**
0400  * cgroup_css - obtain a cgroup's css for the specified subsystem
0401  * @cgrp: the cgroup of interest
0402  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
0403  *
0404  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
0405  * function must be called either under cgroup_mutex or rcu_read_lock() and
0406  * the caller is responsible for pinning the returned css if it wants to
0407  * keep accessing it outside the said locks.  This function may return
0408  * %NULL if @cgrp doesn't have @subsys_id enabled.
0409  */
0410 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
0411                           struct cgroup_subsys *ss)
0412 {
0413     if (ss)
0414         return rcu_dereference_check(cgrp->subsys[ss->id],
0415                     lockdep_is_held(&cgroup_mutex));
0416     else
0417         return &cgrp->self;
0418 }
0419 
0420 /**
0421  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
0422  * @cgrp: the cgroup of interest
0423  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
0424  *
0425  * Similar to cgroup_css() but returns the effective css, which is defined
0426  * as the matching css of the nearest ancestor including self which has @ss
0427  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
0428  * function is guaranteed to return non-NULL css.
0429  */
0430 static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
0431                         struct cgroup_subsys *ss)
0432 {
0433     lockdep_assert_held(&cgroup_mutex);
0434 
0435     if (!ss)
0436         return &cgrp->self;
0437 
0438     /*
0439      * This function is used while updating css associations and thus
0440      * can't test the csses directly.  Test ss_mask.
0441      */
0442     while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
0443         cgrp = cgroup_parent(cgrp);
0444         if (!cgrp)
0445             return NULL;
0446     }
0447 
0448     return cgroup_css(cgrp, ss);
0449 }
0450 
0451 /**
0452  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
0453  * @cgrp: the cgroup of interest
0454  * @ss: the subsystem of interest
0455  *
0456  * Find and get the effective css of @cgrp for @ss.  The effective css is
0457  * defined as the matching css of the nearest ancestor including self which
0458  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
0459  * the root css is returned, so this function always returns a valid css.
0460  * The returned css must be put using css_put().
0461  */
0462 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
0463                          struct cgroup_subsys *ss)
0464 {
0465     struct cgroup_subsys_state *css;
0466 
0467     rcu_read_lock();
0468 
0469     do {
0470         css = cgroup_css(cgrp, ss);
0471 
0472         if (css && css_tryget_online(css))
0473             goto out_unlock;
0474         cgrp = cgroup_parent(cgrp);
0475     } while (cgrp);
0476 
0477     css = init_css_set.subsys[ss->id];
0478     css_get(css);
0479 out_unlock:
0480     rcu_read_unlock();
0481     return css;
0482 }
0483 
0484 /* convenient tests for these bits */
0485 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
0486 {
0487     return !(cgrp->self.flags & CSS_ONLINE);
0488 }
0489 
0490 static void cgroup_get(struct cgroup *cgrp)
0491 {
0492     WARN_ON_ONCE(cgroup_is_dead(cgrp));
0493     css_get(&cgrp->self);
0494 }
0495 
0496 static bool cgroup_tryget(struct cgroup *cgrp)
0497 {
0498     return css_tryget(&cgrp->self);
0499 }
0500 
0501 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
0502 {
0503     struct cgroup *cgrp = of->kn->parent->priv;
0504     struct cftype *cft = of_cft(of);
0505 
0506     /*
0507      * This is open and unprotected implementation of cgroup_css().
0508      * seq_css() is only called from a kernfs file operation which has
0509      * an active reference on the file.  Because all the subsystem
0510      * files are drained before a css is disassociated with a cgroup,
0511      * the matching css from the cgroup's subsys table is guaranteed to
0512      * be and stay valid until the enclosing operation is complete.
0513      */
0514     if (cft->ss)
0515         return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
0516     else
0517         return &cgrp->self;
0518 }
0519 EXPORT_SYMBOL_GPL(of_css);
0520 
0521 static int notify_on_release(const struct cgroup *cgrp)
0522 {
0523     return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
0524 }
0525 
0526 /**
0527  * for_each_css - iterate all css's of a cgroup
0528  * @css: the iteration cursor
0529  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
0530  * @cgrp: the target cgroup to iterate css's of
0531  *
0532  * Should be called under cgroup_[tree_]mutex.
0533  */
0534 #define for_each_css(css, ssid, cgrp)                   \
0535     for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)    \
0536         if (!((css) = rcu_dereference_check(            \
0537                 (cgrp)->subsys[(ssid)],         \
0538                 lockdep_is_held(&cgroup_mutex)))) { }   \
0539         else
0540 
0541 /**
0542  * for_each_e_css - iterate all effective css's of a cgroup
0543  * @css: the iteration cursor
0544  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
0545  * @cgrp: the target cgroup to iterate css's of
0546  *
0547  * Should be called under cgroup_[tree_]mutex.
0548  */
0549 #define for_each_e_css(css, ssid, cgrp)                 \
0550     for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)    \
0551         if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
0552             ;                       \
0553         else
0554 
0555 /**
0556  * for_each_subsys - iterate all enabled cgroup subsystems
0557  * @ss: the iteration cursor
0558  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
0559  */
0560 #define for_each_subsys(ss, ssid)                   \
0561     for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&        \
0562          (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
0563 
0564 /**
0565  * do_each_subsys_mask - filter for_each_subsys with a bitmask
0566  * @ss: the iteration cursor
0567  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
0568  * @ss_mask: the bitmask
0569  *
0570  * The block will only run for cases where the ssid-th bit (1 << ssid) of
0571  * @ss_mask is set.
0572  */
0573 #define do_each_subsys_mask(ss, ssid, ss_mask) do {         \
0574     unsigned long __ss_mask = (ss_mask);                \
0575     if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
0576         (ssid) = 0;                     \
0577         break;                          \
0578     }                               \
0579     for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {   \
0580         (ss) = cgroup_subsys[ssid];             \
0581         {
0582 
0583 #define while_each_subsys_mask()                    \
0584         }                           \
0585     }                               \
0586 } while (false)
0587 
0588 /* iterate across the hierarchies */
0589 #define for_each_root(root)                     \
0590     list_for_each_entry((root), &cgroup_roots, root_list)
0591 
0592 /* iterate over child cgrps, lock should be held throughout iteration */
0593 #define cgroup_for_each_live_child(child, cgrp)             \
0594     list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
0595         if (({ lockdep_assert_held(&cgroup_mutex);      \
0596                cgroup_is_dead(child); }))           \
0597             ;                       \
0598         else
0599 
0600 /* walk live descendants in preorder */
0601 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)      \
0602     css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
0603         if (({ lockdep_assert_held(&cgroup_mutex);      \
0604                (dsct) = (d_css)->cgroup;            \
0605                cgroup_is_dead(dsct); }))            \
0606             ;                       \
0607         else
0608 
0609 /* walk live descendants in postorder */
0610 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)     \
0611     css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
0612         if (({ lockdep_assert_held(&cgroup_mutex);      \
0613                (dsct) = (d_css)->cgroup;            \
0614                cgroup_is_dead(dsct); }))            \
0615             ;                       \
0616         else
0617 
0618 static void cgroup_release_agent(struct work_struct *work);
0619 static void check_for_release(struct cgroup *cgrp);
0620 
0621 /*
0622  * A cgroup can be associated with multiple css_sets as different tasks may
0623  * belong to different cgroups on different hierarchies.  In the other
0624  * direction, a css_set is naturally associated with multiple cgroups.
0625  * This M:N relationship is represented by the following link structure
0626  * which exists for each association and allows traversing the associations
0627  * from both sides.
0628  */
0629 struct cgrp_cset_link {
0630     /* the cgroup and css_set this link associates */
0631     struct cgroup       *cgrp;
0632     struct css_set      *cset;
0633 
0634     /* list of cgrp_cset_links anchored at cgrp->cset_links */
0635     struct list_head    cset_link;
0636 
0637     /* list of cgrp_cset_links anchored at css_set->cgrp_links */
0638     struct list_head    cgrp_link;
0639 };
0640 
0641 /*
0642  * The default css_set - used by init and its children prior to any
0643  * hierarchies being mounted. It contains a pointer to the root state
0644  * for each subsystem. Also used to anchor the list of css_sets. Not
0645  * reference-counted, to improve performance when child cgroups
0646  * haven't been created.
0647  */
0648 struct css_set init_css_set = {
0649     .refcount       = ATOMIC_INIT(1),
0650     .cgrp_links     = LIST_HEAD_INIT(init_css_set.cgrp_links),
0651     .tasks          = LIST_HEAD_INIT(init_css_set.tasks),
0652     .mg_tasks       = LIST_HEAD_INIT(init_css_set.mg_tasks),
0653     .mg_preload_node    = LIST_HEAD_INIT(init_css_set.mg_preload_node),
0654     .mg_node        = LIST_HEAD_INIT(init_css_set.mg_node),
0655     .task_iters     = LIST_HEAD_INIT(init_css_set.task_iters),
0656 };
0657 
0658 static int css_set_count    = 1;    /* 1 for init_css_set */
0659 
0660 /**
0661  * css_set_populated - does a css_set contain any tasks?
0662  * @cset: target css_set
0663  */
0664 static bool css_set_populated(struct css_set *cset)
0665 {
0666     lockdep_assert_held(&css_set_lock);
0667 
0668     return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
0669 }
0670 
0671 /**
0672  * cgroup_update_populated - updated populated count of a cgroup
0673  * @cgrp: the target cgroup
0674  * @populated: inc or dec populated count
0675  *
0676  * One of the css_sets associated with @cgrp is either getting its first
0677  * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
0678  * count is propagated towards root so that a given cgroup's populated_cnt
0679  * is zero iff the cgroup and all its descendants don't contain any tasks.
0680  *
0681  * @cgrp's interface file "cgroup.populated" is zero if
0682  * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
0683  * changes from or to zero, userland is notified that the content of the
0684  * interface file has changed.  This can be used to detect when @cgrp and
0685  * its descendants become populated or empty.
0686  */
0687 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
0688 {
0689     lockdep_assert_held(&css_set_lock);
0690 
0691     do {
0692         bool trigger;
0693 
0694         if (populated)
0695             trigger = !cgrp->populated_cnt++;
0696         else
0697             trigger = !--cgrp->populated_cnt;
0698 
0699         if (!trigger)
0700             break;
0701 
0702         check_for_release(cgrp);
0703         cgroup_file_notify(&cgrp->events_file);
0704 
0705         cgrp = cgroup_parent(cgrp);
0706     } while (cgrp);
0707 }
0708 
0709 /**
0710  * css_set_update_populated - update populated state of a css_set
0711  * @cset: target css_set
0712  * @populated: whether @cset is populated or depopulated
0713  *
0714  * @cset is either getting the first task or losing the last.  Update the
0715  * ->populated_cnt of all associated cgroups accordingly.
0716  */
0717 static void css_set_update_populated(struct css_set *cset, bool populated)
0718 {
0719     struct cgrp_cset_link *link;
0720 
0721     lockdep_assert_held(&css_set_lock);
0722 
0723     list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
0724         cgroup_update_populated(link->cgrp, populated);
0725 }
0726 
0727 /**
0728  * css_set_move_task - move a task from one css_set to another
0729  * @task: task being moved
0730  * @from_cset: css_set @task currently belongs to (may be NULL)
0731  * @to_cset: new css_set @task is being moved to (may be NULL)
0732  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
0733  *
0734  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
0735  * css_set, @from_cset can be NULL.  If @task is being disassociated
0736  * instead of moved, @to_cset can be NULL.
0737  *
0738  * This function automatically handles populated_cnt updates and
0739  * css_task_iter adjustments but the caller is responsible for managing
0740  * @from_cset and @to_cset's reference counts.
0741  */
0742 static void css_set_move_task(struct task_struct *task,
0743                   struct css_set *from_cset, struct css_set *to_cset,
0744                   bool use_mg_tasks)
0745 {
0746     lockdep_assert_held(&css_set_lock);
0747 
0748     if (to_cset && !css_set_populated(to_cset))
0749         css_set_update_populated(to_cset, true);
0750 
0751     if (from_cset) {
0752         struct css_task_iter *it, *pos;
0753 
0754         WARN_ON_ONCE(list_empty(&task->cg_list));
0755 
0756         /*
0757          * @task is leaving, advance task iterators which are
0758          * pointing to it so that they can resume at the next
0759          * position.  Advancing an iterator might remove it from
0760          * the list, use safe walk.  See css_task_iter_advance*()
0761          * for details.
0762          */
0763         list_for_each_entry_safe(it, pos, &from_cset->task_iters,
0764                      iters_node)
0765             if (it->task_pos == &task->cg_list)
0766                 css_task_iter_advance(it);
0767 
0768         list_del_init(&task->cg_list);
0769         if (!css_set_populated(from_cset))
0770             css_set_update_populated(from_cset, false);
0771     } else {
0772         WARN_ON_ONCE(!list_empty(&task->cg_list));
0773     }
0774 
0775     if (to_cset) {
0776         /*
0777          * We are synchronized through cgroup_threadgroup_rwsem
0778          * against PF_EXITING setting such that we can't race
0779          * against cgroup_exit() changing the css_set to
0780          * init_css_set and dropping the old one.
0781          */
0782         WARN_ON_ONCE(task->flags & PF_EXITING);
0783 
0784         rcu_assign_pointer(task->cgroups, to_cset);
0785         list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
0786                                  &to_cset->tasks);
0787     }
0788 }
0789 
0790 /*
0791  * hash table for cgroup groups. This improves the performance to find
0792  * an existing css_set. This hash doesn't (currently) take into
0793  * account cgroups in empty hierarchies.
0794  */
0795 #define CSS_SET_HASH_BITS   7
0796 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
0797 
0798 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
0799 {
0800     unsigned long key = 0UL;
0801     struct cgroup_subsys *ss;
0802     int i;
0803 
0804     for_each_subsys(ss, i)
0805         key += (unsigned long)css[i];
0806     key = (key >> 16) ^ key;
0807 
0808     return key;
0809 }
0810 
0811 static void put_css_set_locked(struct css_set *cset)
0812 {
0813     struct cgrp_cset_link *link, *tmp_link;
0814     struct cgroup_subsys *ss;
0815     int ssid;
0816 
0817     lockdep_assert_held(&css_set_lock);
0818 
0819     if (!atomic_dec_and_test(&cset->refcount))
0820         return;
0821 
0822     /* This css_set is dead. unlink it and release cgroup and css refs */
0823     for_each_subsys(ss, ssid) {
0824         list_del(&cset->e_cset_node[ssid]);
0825         css_put(cset->subsys[ssid]);
0826     }
0827     hash_del(&cset->hlist);
0828     css_set_count--;
0829 
0830     list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
0831         list_del(&link->cset_link);
0832         list_del(&link->cgrp_link);
0833         if (cgroup_parent(link->cgrp))
0834             cgroup_put(link->cgrp);
0835         kfree(link);
0836     }
0837 
0838     kfree_rcu(cset, rcu_head);
0839 }
0840 
0841 static void put_css_set(struct css_set *cset)
0842 {
0843     unsigned long flags;
0844 
0845     /*
0846      * Ensure that the refcount doesn't hit zero while any readers
0847      * can see it. Similar to atomic_dec_and_lock(), but for an
0848      * rwlock
0849      */
0850     if (atomic_add_unless(&cset->refcount, -1, 1))
0851         return;
0852 
0853     spin_lock_irqsave(&css_set_lock, flags);
0854     put_css_set_locked(cset);
0855     spin_unlock_irqrestore(&css_set_lock, flags);
0856 }
0857 
0858 /*
0859  * refcounted get/put for css_set objects
0860  */
0861 static inline void get_css_set(struct css_set *cset)
0862 {
0863     atomic_inc(&cset->refcount);
0864 }
0865 
0866 /**
0867  * compare_css_sets - helper function for find_existing_css_set().
0868  * @cset: candidate css_set being tested
0869  * @old_cset: existing css_set for a task
0870  * @new_cgrp: cgroup that's being entered by the task
0871  * @template: desired set of css pointers in css_set (pre-calculated)
0872  *
0873  * Returns true if "cset" matches "old_cset" except for the hierarchy
0874  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
0875  */
0876 static bool compare_css_sets(struct css_set *cset,
0877                  struct css_set *old_cset,
0878                  struct cgroup *new_cgrp,
0879                  struct cgroup_subsys_state *template[])
0880 {
0881     struct list_head *l1, *l2;
0882 
0883     /*
0884      * On the default hierarchy, there can be csets which are
0885      * associated with the same set of cgroups but different csses.
0886      * Let's first ensure that csses match.
0887      */
0888     if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
0889         return false;
0890 
0891     /*
0892      * Compare cgroup pointers in order to distinguish between
0893      * different cgroups in hierarchies.  As different cgroups may
0894      * share the same effective css, this comparison is always
0895      * necessary.
0896      */
0897     l1 = &cset->cgrp_links;
0898     l2 = &old_cset->cgrp_links;
0899     while (1) {
0900         struct cgrp_cset_link *link1, *link2;
0901         struct cgroup *cgrp1, *cgrp2;
0902 
0903         l1 = l1->next;
0904         l2 = l2->next;
0905         /* See if we reached the end - both lists are equal length. */
0906         if (l1 == &cset->cgrp_links) {
0907             BUG_ON(l2 != &old_cset->cgrp_links);
0908             break;
0909         } else {
0910             BUG_ON(l2 == &old_cset->cgrp_links);
0911         }
0912         /* Locate the cgroups associated with these links. */
0913         link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
0914         link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
0915         cgrp1 = link1->cgrp;
0916         cgrp2 = link2->cgrp;
0917         /* Hierarchies should be linked in the same order. */
0918         BUG_ON(cgrp1->root != cgrp2->root);
0919 
0920         /*
0921          * If this hierarchy is the hierarchy of the cgroup
0922          * that's changing, then we need to check that this
0923          * css_set points to the new cgroup; if it's any other
0924          * hierarchy, then this css_set should point to the
0925          * same cgroup as the old css_set.
0926          */
0927         if (cgrp1->root == new_cgrp->root) {
0928             if (cgrp1 != new_cgrp)
0929                 return false;
0930         } else {
0931             if (cgrp1 != cgrp2)
0932                 return false;
0933         }
0934     }
0935     return true;
0936 }
0937 
0938 /**
0939  * find_existing_css_set - init css array and find the matching css_set
0940  * @old_cset: the css_set that we're using before the cgroup transition
0941  * @cgrp: the cgroup that we're moving into
0942  * @template: out param for the new set of csses, should be clear on entry
0943  */
0944 static struct css_set *find_existing_css_set(struct css_set *old_cset,
0945                     struct cgroup *cgrp,
0946                     struct cgroup_subsys_state *template[])
0947 {
0948     struct cgroup_root *root = cgrp->root;
0949     struct cgroup_subsys *ss;
0950     struct css_set *cset;
0951     unsigned long key;
0952     int i;
0953 
0954     /*
0955      * Build the set of subsystem state objects that we want to see in the
0956      * new css_set. while subsystems can change globally, the entries here
0957      * won't change, so no need for locking.
0958      */
0959     for_each_subsys(ss, i) {
0960         if (root->subsys_mask & (1UL << i)) {
0961             /*
0962              * @ss is in this hierarchy, so we want the
0963              * effective css from @cgrp.
0964              */
0965             template[i] = cgroup_e_css(cgrp, ss);
0966         } else {
0967             /*
0968              * @ss is not in this hierarchy, so we don't want
0969              * to change the css.
0970              */
0971             template[i] = old_cset->subsys[i];
0972         }
0973     }
0974 
0975     key = css_set_hash(template);
0976     hash_for_each_possible(css_set_table, cset, hlist, key) {
0977         if (!compare_css_sets(cset, old_cset, cgrp, template))
0978             continue;
0979 
0980         /* This css_set matches what we need */
0981         return cset;
0982     }
0983 
0984     /* No existing cgroup group matched */
0985     return NULL;
0986 }
0987 
0988 static void free_cgrp_cset_links(struct list_head *links_to_free)
0989 {
0990     struct cgrp_cset_link *link, *tmp_link;
0991 
0992     list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
0993         list_del(&link->cset_link);
0994         kfree(link);
0995     }
0996 }
0997 
0998 /**
0999  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1000  * @count: the number of links to allocate
1001  * @tmp_links: list_head the allocated links are put on
1002  *
1003  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1004  * through ->cset_link.  Returns 0 on success or -errno.
1005  */
1006 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1007 {
1008     struct cgrp_cset_link *link;
1009     int i;
1010 
1011     INIT_LIST_HEAD(tmp_links);
1012 
1013     for (i = 0; i < count; i++) {
1014         link = kzalloc(sizeof(*link), GFP_KERNEL);
1015         if (!link) {
1016             free_cgrp_cset_links(tmp_links);
1017             return -ENOMEM;
1018         }
1019         list_add(&link->cset_link, tmp_links);
1020     }
1021     return 0;
1022 }
1023 
1024 /**
1025  * link_css_set - a helper function to link a css_set to a cgroup
1026  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1027  * @cset: the css_set to be linked
1028  * @cgrp: the destination cgroup
1029  */
1030 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1031              struct cgroup *cgrp)
1032 {
1033     struct cgrp_cset_link *link;
1034 
1035     BUG_ON(list_empty(tmp_links));
1036 
1037     if (cgroup_on_dfl(cgrp))
1038         cset->dfl_cgrp = cgrp;
1039 
1040     link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1041     link->cset = cset;
1042     link->cgrp = cgrp;
1043 
1044     /*
1045      * Always add links to the tail of the lists so that the lists are
1046      * in choronological order.
1047      */
1048     list_move_tail(&link->cset_link, &cgrp->cset_links);
1049     list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1050 
1051     if (cgroup_parent(cgrp))
1052         cgroup_get(cgrp);
1053 }
1054 
1055 /**
1056  * find_css_set - return a new css_set with one cgroup updated
1057  * @old_cset: the baseline css_set
1058  * @cgrp: the cgroup to be updated
1059  *
1060  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1061  * substituted into the appropriate hierarchy.
1062  */
1063 static struct css_set *find_css_set(struct css_set *old_cset,
1064                     struct cgroup *cgrp)
1065 {
1066     struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1067     struct css_set *cset;
1068     struct list_head tmp_links;
1069     struct cgrp_cset_link *link;
1070     struct cgroup_subsys *ss;
1071     unsigned long key;
1072     int ssid;
1073 
1074     lockdep_assert_held(&cgroup_mutex);
1075 
1076     /* First see if we already have a cgroup group that matches
1077      * the desired set */
1078     spin_lock_irq(&css_set_lock);
1079     cset = find_existing_css_set(old_cset, cgrp, template);
1080     if (cset)
1081         get_css_set(cset);
1082     spin_unlock_irq(&css_set_lock);
1083 
1084     if (cset)
1085         return cset;
1086 
1087     cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1088     if (!cset)
1089         return NULL;
1090 
1091     /* Allocate all the cgrp_cset_link objects that we'll need */
1092     if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1093         kfree(cset);
1094         return NULL;
1095     }
1096 
1097     atomic_set(&cset->refcount, 1);
1098     INIT_LIST_HEAD(&cset->cgrp_links);
1099     INIT_LIST_HEAD(&cset->tasks);
1100     INIT_LIST_HEAD(&cset->mg_tasks);
1101     INIT_LIST_HEAD(&cset->mg_preload_node);
1102     INIT_LIST_HEAD(&cset->mg_node);
1103     INIT_LIST_HEAD(&cset->task_iters);
1104     INIT_HLIST_NODE(&cset->hlist);
1105 
1106     /* Copy the set of subsystem state objects generated in
1107      * find_existing_css_set() */
1108     memcpy(cset->subsys, template, sizeof(cset->subsys));
1109 
1110     spin_lock_irq(&css_set_lock);
1111     /* Add reference counts and links from the new css_set. */
1112     list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1113         struct cgroup *c = link->cgrp;
1114 
1115         if (c->root == cgrp->root)
1116             c = cgrp;
1117         link_css_set(&tmp_links, cset, c);
1118     }
1119 
1120     BUG_ON(!list_empty(&tmp_links));
1121 
1122     css_set_count++;
1123 
1124     /* Add @cset to the hash table */
1125     key = css_set_hash(cset->subsys);
1126     hash_add(css_set_table, &cset->hlist, key);
1127 
1128     for_each_subsys(ss, ssid) {
1129         struct cgroup_subsys_state *css = cset->subsys[ssid];
1130 
1131         list_add_tail(&cset->e_cset_node[ssid],
1132                   &css->cgroup->e_csets[ssid]);
1133         css_get(css);
1134     }
1135 
1136     spin_unlock_irq(&css_set_lock);
1137 
1138     return cset;
1139 }
1140 
1141 static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1142 {
1143     struct cgroup *root_cgrp = kf_root->kn->priv;
1144 
1145     return root_cgrp->root;
1146 }
1147 
1148 static int cgroup_init_root_id(struct cgroup_root *root)
1149 {
1150     int id;
1151 
1152     lockdep_assert_held(&cgroup_mutex);
1153 
1154     id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1155     if (id < 0)
1156         return id;
1157 
1158     root->hierarchy_id = id;
1159     return 0;
1160 }
1161 
1162 static void cgroup_exit_root_id(struct cgroup_root *root)
1163 {
1164     lockdep_assert_held(&cgroup_mutex);
1165 
1166     idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1167 }
1168 
1169 static void cgroup_free_root(struct cgroup_root *root)
1170 {
1171     if (root) {
1172         idr_destroy(&root->cgroup_idr);
1173         kfree(root);
1174     }
1175 }
1176 
1177 static void cgroup_destroy_root(struct cgroup_root *root)
1178 {
1179     struct cgroup *cgrp = &root->cgrp;
1180     struct cgrp_cset_link *link, *tmp_link;
1181 
1182     trace_cgroup_destroy_root(root);
1183 
1184     cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1185 
1186     BUG_ON(atomic_read(&root->nr_cgrps));
1187     BUG_ON(!list_empty(&cgrp->self.children));
1188 
1189     /* Rebind all subsystems back to the default hierarchy */
1190     WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1191 
1192     /*
1193      * Release all the links from cset_links to this hierarchy's
1194      * root cgroup
1195      */
1196     spin_lock_irq(&css_set_lock);
1197 
1198     list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1199         list_del(&link->cset_link);
1200         list_del(&link->cgrp_link);
1201         kfree(link);
1202     }
1203 
1204     spin_unlock_irq(&css_set_lock);
1205 
1206     if (!list_empty(&root->root_list)) {
1207         list_del(&root->root_list);
1208         cgroup_root_count--;
1209     }
1210 
1211     cgroup_exit_root_id(root);
1212 
1213     mutex_unlock(&cgroup_mutex);
1214 
1215     kernfs_destroy_root(root->kf_root);
1216     cgroup_free_root(root);
1217 }
1218 
1219 /*
1220  * look up cgroup associated with current task's cgroup namespace on the
1221  * specified hierarchy
1222  */
1223 static struct cgroup *
1224 current_cgns_cgroup_from_root(struct cgroup_root *root)
1225 {
1226     struct cgroup *res = NULL;
1227     struct css_set *cset;
1228 
1229     lockdep_assert_held(&css_set_lock);
1230 
1231     rcu_read_lock();
1232 
1233     cset = current->nsproxy->cgroup_ns->root_cset;
1234     if (cset == &init_css_set) {
1235         res = &root->cgrp;
1236     } else {
1237         struct cgrp_cset_link *link;
1238 
1239         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1240             struct cgroup *c = link->cgrp;
1241 
1242             if (c->root == root) {
1243                 res = c;
1244                 break;
1245             }
1246         }
1247     }
1248     rcu_read_unlock();
1249 
1250     BUG_ON(!res);
1251     return res;
1252 }
1253 
1254 /* look up cgroup associated with given css_set on the specified hierarchy */
1255 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1256                         struct cgroup_root *root)
1257 {
1258     struct cgroup *res = NULL;
1259 
1260     lockdep_assert_held(&cgroup_mutex);
1261     lockdep_assert_held(&css_set_lock);
1262 
1263     if (cset == &init_css_set) {
1264         res = &root->cgrp;
1265     } else {
1266         struct cgrp_cset_link *link;
1267 
1268         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1269             struct cgroup *c = link->cgrp;
1270 
1271             if (c->root == root) {
1272                 res = c;
1273                 break;
1274             }
1275         }
1276     }
1277 
1278     BUG_ON(!res);
1279     return res;
1280 }
1281 
1282 /*
1283  * Return the cgroup for "task" from the given hierarchy. Must be
1284  * called with cgroup_mutex and css_set_lock held.
1285  */
1286 static struct cgroup *task_cgroup_from_root(struct task_struct *task,
1287                         struct cgroup_root *root)
1288 {
1289     /*
1290      * No need to lock the task - since we hold cgroup_mutex the
1291      * task can't change groups, so the only thing that can happen
1292      * is that it exits and its css is set back to init_css_set.
1293      */
1294     return cset_cgroup_from_root(task_css_set(task), root);
1295 }
1296 
1297 /*
1298  * A task must hold cgroup_mutex to modify cgroups.
1299  *
1300  * Any task can increment and decrement the count field without lock.
1301  * So in general, code holding cgroup_mutex can't rely on the count
1302  * field not changing.  However, if the count goes to zero, then only
1303  * cgroup_attach_task() can increment it again.  Because a count of zero
1304  * means that no tasks are currently attached, therefore there is no
1305  * way a task attached to that cgroup can fork (the other way to
1306  * increment the count).  So code holding cgroup_mutex can safely
1307  * assume that if the count is zero, it will stay zero. Similarly, if
1308  * a task holds cgroup_mutex on a cgroup with zero count, it
1309  * knows that the cgroup won't be removed, as cgroup_rmdir()
1310  * needs that mutex.
1311  *
1312  * A cgroup can only be deleted if both its 'count' of using tasks
1313  * is zero, and its list of 'children' cgroups is empty.  Since all
1314  * tasks in the system use _some_ cgroup, and since there is always at
1315  * least one task in the system (init, pid == 1), therefore, root cgroup
1316  * always has either children cgroups and/or using tasks.  So we don't
1317  * need a special hack to ensure that root cgroup cannot be deleted.
1318  *
1319  * P.S.  One more locking exception.  RCU is used to guard the
1320  * update of a tasks cgroup pointer by cgroup_attach_task()
1321  */
1322 
1323 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1324 static const struct file_operations proc_cgroupstats_operations;
1325 
1326 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1327                   char *buf)
1328 {
1329     struct cgroup_subsys *ss = cft->ss;
1330 
1331     if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1332         !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1333         snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1334              cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1335              cft->name);
1336     else
1337         strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1338     return buf;
1339 }
1340 
1341 /**
1342  * cgroup_file_mode - deduce file mode of a control file
1343  * @cft: the control file in question
1344  *
1345  * S_IRUGO for read, S_IWUSR for write.
1346  */
1347 static umode_t cgroup_file_mode(const struct cftype *cft)
1348 {
1349     umode_t mode = 0;
1350 
1351     if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1352         mode |= S_IRUGO;
1353 
1354     if (cft->write_u64 || cft->write_s64 || cft->write) {
1355         if (cft->flags & CFTYPE_WORLD_WRITABLE)
1356             mode |= S_IWUGO;
1357         else
1358             mode |= S_IWUSR;
1359     }
1360 
1361     return mode;
1362 }
1363 
1364 /**
1365  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1366  * @subtree_control: the new subtree_control mask to consider
1367  * @this_ss_mask: available subsystems
1368  *
1369  * On the default hierarchy, a subsystem may request other subsystems to be
1370  * enabled together through its ->depends_on mask.  In such cases, more
1371  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1372  *
1373  * This function calculates which subsystems need to be enabled if
1374  * @subtree_control is to be applied while restricted to @this_ss_mask.
1375  */
1376 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1377 {
1378     u16 cur_ss_mask = subtree_control;
1379     struct cgroup_subsys *ss;
1380     int ssid;
1381 
1382     lockdep_assert_held(&cgroup_mutex);
1383 
1384     cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1385 
1386     while (true) {
1387         u16 new_ss_mask = cur_ss_mask;
1388 
1389         do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1390             new_ss_mask |= ss->depends_on;
1391         } while_each_subsys_mask();
1392 
1393         /*
1394          * Mask out subsystems which aren't available.  This can
1395          * happen only if some depended-upon subsystems were bound
1396          * to non-default hierarchies.
1397          */
1398         new_ss_mask &= this_ss_mask;
1399 
1400         if (new_ss_mask == cur_ss_mask)
1401             break;
1402         cur_ss_mask = new_ss_mask;
1403     }
1404 
1405     return cur_ss_mask;
1406 }
1407 
1408 /**
1409  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1410  * @kn: the kernfs_node being serviced
1411  *
1412  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1413  * the method finishes if locking succeeded.  Note that once this function
1414  * returns the cgroup returned by cgroup_kn_lock_live() may become
1415  * inaccessible any time.  If the caller intends to continue to access the
1416  * cgroup, it should pin it before invoking this function.
1417  */
1418 static void cgroup_kn_unlock(struct kernfs_node *kn)
1419 {
1420     struct cgroup *cgrp;
1421 
1422     if (kernfs_type(kn) == KERNFS_DIR)
1423         cgrp = kn->priv;
1424     else
1425         cgrp = kn->parent->priv;
1426 
1427     mutex_unlock(&cgroup_mutex);
1428 
1429     kernfs_unbreak_active_protection(kn);
1430     cgroup_put(cgrp);
1431 }
1432 
1433 /**
1434  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1435  * @kn: the kernfs_node being serviced
1436  * @drain_offline: perform offline draining on the cgroup
1437  *
1438  * This helper is to be used by a cgroup kernfs method currently servicing
1439  * @kn.  It breaks the active protection, performs cgroup locking and
1440  * verifies that the associated cgroup is alive.  Returns the cgroup if
1441  * alive; otherwise, %NULL.  A successful return should be undone by a
1442  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1443  * cgroup is drained of offlining csses before return.
1444  *
1445  * Any cgroup kernfs method implementation which requires locking the
1446  * associated cgroup should use this helper.  It avoids nesting cgroup
1447  * locking under kernfs active protection and allows all kernfs operations
1448  * including self-removal.
1449  */
1450 static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn,
1451                       bool drain_offline)
1452 {
1453     struct cgroup *cgrp;
1454 
1455     if (kernfs_type(kn) == KERNFS_DIR)
1456         cgrp = kn->priv;
1457     else
1458         cgrp = kn->parent->priv;
1459 
1460     /*
1461      * We're gonna grab cgroup_mutex which nests outside kernfs
1462      * active_ref.  cgroup liveliness check alone provides enough
1463      * protection against removal.  Ensure @cgrp stays accessible and
1464      * break the active_ref protection.
1465      */
1466     if (!cgroup_tryget(cgrp))
1467         return NULL;
1468     kernfs_break_active_protection(kn);
1469 
1470     if (drain_offline)
1471         cgroup_lock_and_drain_offline(cgrp);
1472     else
1473         mutex_lock(&cgroup_mutex);
1474 
1475     if (!cgroup_is_dead(cgrp))
1476         return cgrp;
1477 
1478     cgroup_kn_unlock(kn);
1479     return NULL;
1480 }
1481 
1482 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1483 {
1484     char name[CGROUP_FILE_NAME_MAX];
1485 
1486     lockdep_assert_held(&cgroup_mutex);
1487 
1488     if (cft->file_offset) {
1489         struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1490         struct cgroup_file *cfile = (void *)css + cft->file_offset;
1491 
1492         spin_lock_irq(&cgroup_file_kn_lock);
1493         cfile->kn = NULL;
1494         spin_unlock_irq(&cgroup_file_kn_lock);
1495     }
1496 
1497     kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1498 }
1499 
1500 /**
1501  * css_clear_dir - remove subsys files in a cgroup directory
1502  * @css: taget css
1503  */
1504 static void css_clear_dir(struct cgroup_subsys_state *css)
1505 {
1506     struct cgroup *cgrp = css->cgroup;
1507     struct cftype *cfts;
1508 
1509     if (!(css->flags & CSS_VISIBLE))
1510         return;
1511 
1512     css->flags &= ~CSS_VISIBLE;
1513 
1514     list_for_each_entry(cfts, &css->ss->cfts, node)
1515         cgroup_addrm_files(css, cgrp, cfts, false);
1516 }
1517 
1518 /**
1519  * css_populate_dir - create subsys files in a cgroup directory
1520  * @css: target css
1521  *
1522  * On failure, no file is added.
1523  */
1524 static int css_populate_dir(struct cgroup_subsys_state *css)
1525 {
1526     struct cgroup *cgrp = css->cgroup;
1527     struct cftype *cfts, *failed_cfts;
1528     int ret;
1529 
1530     if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1531         return 0;
1532 
1533     if (!css->ss) {
1534         if (cgroup_on_dfl(cgrp))
1535             cfts = cgroup_dfl_base_files;
1536         else
1537             cfts = cgroup_legacy_base_files;
1538 
1539         return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1540     }
1541 
1542     list_for_each_entry(cfts, &css->ss->cfts, node) {
1543         ret = cgroup_addrm_files(css, cgrp, cfts, true);
1544         if (ret < 0) {
1545             failed_cfts = cfts;
1546             goto err;
1547         }
1548     }
1549 
1550     css->flags |= CSS_VISIBLE;
1551 
1552     return 0;
1553 err:
1554     list_for_each_entry(cfts, &css->ss->cfts, node) {
1555         if (cfts == failed_cfts)
1556             break;
1557         cgroup_addrm_files(css, cgrp, cfts, false);
1558     }
1559     return ret;
1560 }
1561 
1562 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1563 {
1564     struct cgroup *dcgrp = &dst_root->cgrp;
1565     struct cgroup_subsys *ss;
1566     int ssid, i, ret;
1567 
1568     lockdep_assert_held(&cgroup_mutex);
1569 
1570     do_each_subsys_mask(ss, ssid, ss_mask) {
1571         /*
1572          * If @ss has non-root csses attached to it, can't move.
1573          * If @ss is an implicit controller, it is exempt from this
1574          * rule and can be stolen.
1575          */
1576         if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1577             !ss->implicit_on_dfl)
1578             return -EBUSY;
1579 
1580         /* can't move between two non-dummy roots either */
1581         if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1582             return -EBUSY;
1583     } while_each_subsys_mask();
1584 
1585     do_each_subsys_mask(ss, ssid, ss_mask) {
1586         struct cgroup_root *src_root = ss->root;
1587         struct cgroup *scgrp = &src_root->cgrp;
1588         struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1589         struct css_set *cset;
1590 
1591         WARN_ON(!css || cgroup_css(dcgrp, ss));
1592 
1593         /* disable from the source */
1594         src_root->subsys_mask &= ~(1 << ssid);
1595         WARN_ON(cgroup_apply_control(scgrp));
1596         cgroup_finalize_control(scgrp, 0);
1597 
1598         /* rebind */
1599         RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1600         rcu_assign_pointer(dcgrp->subsys[ssid], css);
1601         ss->root = dst_root;
1602         css->cgroup = dcgrp;
1603 
1604         spin_lock_irq(&css_set_lock);
1605         hash_for_each(css_set_table, i, cset, hlist)
1606             list_move_tail(&cset->e_cset_node[ss->id],
1607                        &dcgrp->e_csets[ss->id]);
1608         spin_unlock_irq(&css_set_lock);
1609 
1610         /* default hierarchy doesn't enable controllers by default */
1611         dst_root->subsys_mask |= 1 << ssid;
1612         if (dst_root == &cgrp_dfl_root) {
1613             static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1614         } else {
1615             dcgrp->subtree_control |= 1 << ssid;
1616             static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1617         }
1618 
1619         ret = cgroup_apply_control(dcgrp);
1620         if (ret)
1621             pr_warn("partial failure to rebind %s controller (err=%d)\n",
1622                 ss->name, ret);
1623 
1624         if (ss->bind)
1625             ss->bind(css);
1626     } while_each_subsys_mask();
1627 
1628     kernfs_activate(dcgrp->kn);
1629     return 0;
1630 }
1631 
1632 static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1633                 struct kernfs_root *kf_root)
1634 {
1635     int len = 0;
1636     char *buf = NULL;
1637     struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1638     struct cgroup *ns_cgroup;
1639 
1640     buf = kmalloc(PATH_MAX, GFP_KERNEL);
1641     if (!buf)
1642         return -ENOMEM;
1643 
1644     spin_lock_irq(&css_set_lock);
1645     ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1646     len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1647     spin_unlock_irq(&css_set_lock);
1648 
1649     if (len >= PATH_MAX)
1650         len = -ERANGE;
1651     else if (len > 0) {
1652         seq_escape(sf, buf, " \t\n\\");
1653         len = 0;
1654     }
1655     kfree(buf);
1656     return len;
1657 }
1658 
1659 static int cgroup_show_options(struct seq_file *seq,
1660                    struct kernfs_root *kf_root)
1661 {
1662     struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1663     struct cgroup_subsys *ss;
1664     int ssid;
1665 
1666     if (root != &cgrp_dfl_root)
1667         for_each_subsys(ss, ssid)
1668             if (root->subsys_mask & (1 << ssid))
1669                 seq_show_option(seq, ss->legacy_name, NULL);
1670     if (root->flags & CGRP_ROOT_NOPREFIX)
1671         seq_puts(seq, ",noprefix");
1672     if (root->flags & CGRP_ROOT_XATTR)
1673         seq_puts(seq, ",xattr");
1674 
1675     spin_lock(&release_agent_path_lock);
1676     if (strlen(root->release_agent_path))
1677         seq_show_option(seq, "release_agent",
1678                 root->release_agent_path);
1679     spin_unlock(&release_agent_path_lock);
1680 
1681     if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1682         seq_puts(seq, ",clone_children");
1683     if (strlen(root->name))
1684         seq_show_option(seq, "name", root->name);
1685     return 0;
1686 }
1687 
1688 struct cgroup_sb_opts {
1689     u16 subsys_mask;
1690     unsigned int flags;
1691     char *release_agent;
1692     bool cpuset_clone_children;
1693     char *name;
1694     /* User explicitly requested empty subsystem */
1695     bool none;
1696 };
1697 
1698 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1699 {
1700     char *token, *o = data;
1701     bool all_ss = false, one_ss = false;
1702     u16 mask = U16_MAX;
1703     struct cgroup_subsys *ss;
1704     int nr_opts = 0;
1705     int i;
1706 
1707 #ifdef CONFIG_CPUSETS
1708     mask = ~((u16)1 << cpuset_cgrp_id);
1709 #endif
1710 
1711     memset(opts, 0, sizeof(*opts));
1712 
1713     while ((token = strsep(&o, ",")) != NULL) {
1714         nr_opts++;
1715 
1716         if (!*token)
1717             return -EINVAL;
1718         if (!strcmp(token, "none")) {
1719             /* Explicitly have no subsystems */
1720             opts->none = true;
1721             continue;
1722         }
1723         if (!strcmp(token, "all")) {
1724             /* Mutually exclusive option 'all' + subsystem name */
1725             if (one_ss)
1726                 return -EINVAL;
1727             all_ss = true;
1728             continue;
1729         }
1730         if (!strcmp(token, "noprefix")) {
1731             opts->flags |= CGRP_ROOT_NOPREFIX;
1732             continue;
1733         }
1734         if (!strcmp(token, "clone_children")) {
1735             opts->cpuset_clone_children = true;
1736             continue;
1737         }
1738         if (!strcmp(token, "xattr")) {
1739             opts->flags |= CGRP_ROOT_XATTR;
1740             continue;
1741         }
1742         if (!strncmp(token, "release_agent=", 14)) {
1743             /* Specifying two release agents is forbidden */
1744             if (opts->release_agent)
1745                 return -EINVAL;
1746             opts->release_agent =
1747                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1748             if (!opts->release_agent)
1749                 return -ENOMEM;
1750             continue;
1751         }
1752         if (!strncmp(token, "name=", 5)) {
1753             const char *name = token + 5;
1754             /* Can't specify an empty name */
1755             if (!strlen(name))
1756                 return -EINVAL;
1757             /* Must match [\w.-]+ */
1758             for (i = 0; i < strlen(name); i++) {
1759                 char c = name[i];
1760                 if (isalnum(c))
1761                     continue;
1762                 if ((c == '.') || (c == '-') || (c == '_'))
1763                     continue;
1764                 return -EINVAL;
1765             }
1766             /* Specifying two names is forbidden */
1767             if (opts->name)
1768                 return -EINVAL;
1769             opts->name = kstrndup(name,
1770                           MAX_CGROUP_ROOT_NAMELEN - 1,
1771                           GFP_KERNEL);
1772             if (!opts->name)
1773                 return -ENOMEM;
1774 
1775             continue;
1776         }
1777 
1778         for_each_subsys(ss, i) {
1779             if (strcmp(token, ss->legacy_name))
1780                 continue;
1781             if (!cgroup_ssid_enabled(i))
1782                 continue;
1783             if (cgroup_ssid_no_v1(i))
1784                 continue;
1785 
1786             /* Mutually exclusive option 'all' + subsystem name */
1787             if (all_ss)
1788                 return -EINVAL;
1789             opts->subsys_mask |= (1 << i);
1790             one_ss = true;
1791 
1792             break;
1793         }
1794         if (i == CGROUP_SUBSYS_COUNT)
1795             return -ENOENT;
1796     }
1797 
1798     /*
1799      * If the 'all' option was specified select all the subsystems,
1800      * otherwise if 'none', 'name=' and a subsystem name options were
1801      * not specified, let's default to 'all'
1802      */
1803     if (all_ss || (!one_ss && !opts->none && !opts->name))
1804         for_each_subsys(ss, i)
1805             if (cgroup_ssid_enabled(i) && !cgroup_ssid_no_v1(i))
1806                 opts->subsys_mask |= (1 << i);
1807 
1808     /*
1809      * We either have to specify by name or by subsystems. (So all
1810      * empty hierarchies must have a name).
1811      */
1812     if (!opts->subsys_mask && !opts->name)
1813         return -EINVAL;
1814 
1815     /*
1816      * Option noprefix was introduced just for backward compatibility
1817      * with the old cpuset, so we allow noprefix only if mounting just
1818      * the cpuset subsystem.
1819      */
1820     if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1821         return -EINVAL;
1822 
1823     /* Can't specify "none" and some subsystems */
1824     if (opts->subsys_mask && opts->none)
1825         return -EINVAL;
1826 
1827     return 0;
1828 }
1829 
1830 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1831 {
1832     int ret = 0;
1833     struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1834     struct cgroup_sb_opts opts;
1835     u16 added_mask, removed_mask;
1836 
1837     if (root == &cgrp_dfl_root) {
1838         pr_err("remount is not allowed\n");
1839         return -EINVAL;
1840     }
1841 
1842     cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1843 
1844     /* See what subsystems are wanted */
1845     ret = parse_cgroupfs_options(data, &opts);
1846     if (ret)
1847         goto out_unlock;
1848 
1849     if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1850         pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1851             task_tgid_nr(current), current->comm);
1852 
1853     added_mask = opts.subsys_mask & ~root->subsys_mask;
1854     removed_mask = root->subsys_mask & ~opts.subsys_mask;
1855 
1856     /* Don't allow flags or name to change at remount */
1857     if ((opts.flags ^ root->flags) ||
1858         (opts.name && strcmp(opts.name, root->name))) {
1859         pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1860                opts.flags, opts.name ?: "", root->flags, root->name);
1861         ret = -EINVAL;
1862         goto out_unlock;
1863     }
1864 
1865     /* remounting is not allowed for populated hierarchies */
1866     if (!list_empty(&root->cgrp.self.children)) {
1867         ret = -EBUSY;
1868         goto out_unlock;
1869     }
1870 
1871     ret = rebind_subsystems(root, added_mask);
1872     if (ret)
1873         goto out_unlock;
1874 
1875     WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1876 
1877     if (opts.release_agent) {
1878         spin_lock(&release_agent_path_lock);
1879         strcpy(root->release_agent_path, opts.release_agent);
1880         spin_unlock(&release_agent_path_lock);
1881     }
1882 
1883     trace_cgroup_remount(root);
1884 
1885  out_unlock:
1886     kfree(opts.release_agent);
1887     kfree(opts.name);
1888     mutex_unlock(&cgroup_mutex);
1889     return ret;
1890 }
1891 
1892 /*
1893  * To reduce the fork() overhead for systems that are not actually using
1894  * their cgroups capability, we don't maintain the lists running through
1895  * each css_set to its tasks until we see the list actually used - in other
1896  * words after the first mount.
1897  */
1898 static bool use_task_css_set_links __read_mostly;
1899 
1900 static void cgroup_enable_task_cg_lists(void)
1901 {
1902     struct task_struct *p, *g;
1903 
1904     spin_lock_irq(&css_set_lock);
1905 
1906     if (use_task_css_set_links)
1907         goto out_unlock;
1908 
1909     use_task_css_set_links = true;
1910 
1911     /*
1912      * We need tasklist_lock because RCU is not safe against
1913      * while_each_thread(). Besides, a forking task that has passed
1914      * cgroup_post_fork() without seeing use_task_css_set_links = 1
1915      * is not guaranteed to have its child immediately visible in the
1916      * tasklist if we walk through it with RCU.
1917      */
1918     read_lock(&tasklist_lock);
1919     do_each_thread(g, p) {
1920         WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1921                  task_css_set(p) != &init_css_set);
1922 
1923         /*
1924          * We should check if the process is exiting, otherwise
1925          * it will race with cgroup_exit() in that the list
1926          * entry won't be deleted though the process has exited.
1927          * Do it while holding siglock so that we don't end up
1928          * racing against cgroup_exit().
1929          *
1930          * Interrupts were already disabled while acquiring
1931          * the css_set_lock, so we do not need to disable it
1932          * again when acquiring the sighand->siglock here.
1933          */
1934         spin_lock(&p->sighand->siglock);
1935         if (!(p->flags & PF_EXITING)) {
1936             struct css_set *cset = task_css_set(p);
1937 
1938             if (!css_set_populated(cset))
1939                 css_set_update_populated(cset, true);
1940             list_add_tail(&p->cg_list, &cset->tasks);
1941             get_css_set(cset);
1942         }
1943         spin_unlock(&p->sighand->siglock);
1944     } while_each_thread(g, p);
1945     read_unlock(&tasklist_lock);
1946 out_unlock:
1947     spin_unlock_irq(&css_set_lock);
1948 }
1949 
1950 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1951 {
1952     struct cgroup_subsys *ss;
1953     int ssid;
1954 
1955     INIT_LIST_HEAD(&cgrp->self.sibling);
1956     INIT_LIST_HEAD(&cgrp->self.children);
1957     INIT_LIST_HEAD(&cgrp->cset_links);
1958     INIT_LIST_HEAD(&cgrp->pidlists);
1959     mutex_init(&cgrp->pidlist_mutex);
1960     cgrp->self.cgroup = cgrp;
1961     cgrp->self.flags |= CSS_ONLINE;
1962 
1963     for_each_subsys(ss, ssid)
1964         INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1965 
1966     init_waitqueue_head(&cgrp->offline_waitq);
1967     INIT_WORK(&cgrp->release_agent_work, cgroup_release_agent);
1968 }
1969 
1970 static void init_cgroup_root(struct cgroup_root *root,
1971                  struct cgroup_sb_opts *opts)
1972 {
1973     struct cgroup *cgrp = &root->cgrp;
1974 
1975     INIT_LIST_HEAD(&root->root_list);
1976     atomic_set(&root->nr_cgrps, 1);
1977     cgrp->root = root;
1978     init_cgroup_housekeeping(cgrp);
1979     idr_init(&root->cgroup_idr);
1980 
1981     root->flags = opts->flags;
1982     if (opts->release_agent)
1983         strcpy(root->release_agent_path, opts->release_agent);
1984     if (opts->name)
1985         strcpy(root->name, opts->name);
1986     if (opts->cpuset_clone_children)
1987         set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988 }
1989 
1990 static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1991 {
1992     LIST_HEAD(tmp_links);
1993     struct cgroup *root_cgrp = &root->cgrp;
1994     struct css_set *cset;
1995     int i, ret;
1996 
1997     lockdep_assert_held(&cgroup_mutex);
1998 
1999     ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2000     if (ret < 0)
2001         goto out;
2002     root_cgrp->id = ret;
2003     root_cgrp->ancestor_ids[0] = ret;
2004 
2005     ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
2006                   GFP_KERNEL);
2007     if (ret)
2008         goto out;
2009 
2010     /*
2011      * We're accessing css_set_count without locking css_set_lock here,
2012      * but that's OK - it can only be increased by someone holding
2013      * cgroup_lock, and that's us.  Later rebinding may disable
2014      * controllers on the default hierarchy and thus create new csets,
2015      * which can't be more than the existing ones.  Allocate 2x.
2016      */
2017     ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2018     if (ret)
2019         goto cancel_ref;
2020 
2021     ret = cgroup_init_root_id(root);
2022     if (ret)
2023         goto cancel_ref;
2024 
2025     root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
2026                        KERNFS_ROOT_CREATE_DEACTIVATED,
2027                        root_cgrp);
2028     if (IS_ERR(root->kf_root)) {
2029         ret = PTR_ERR(root->kf_root);
2030         goto exit_root_id;
2031     }
2032     root_cgrp->kn = root->kf_root->kn;
2033 
2034     ret = css_populate_dir(&root_cgrp->self);
2035     if (ret)
2036         goto destroy_root;
2037 
2038     ret = rebind_subsystems(root, ss_mask);
2039     if (ret)
2040         goto destroy_root;
2041 
2042     trace_cgroup_setup_root(root);
2043 
2044     /*
2045      * There must be no failure case after here, since rebinding takes
2046      * care of subsystems' refcounts, which are explicitly dropped in
2047      * the failure exit path.
2048      */
2049     list_add(&root->root_list, &cgroup_roots);
2050     cgroup_root_count++;
2051 
2052     /*
2053      * Link the root cgroup in this hierarchy into all the css_set
2054      * objects.
2055      */
2056     spin_lock_irq(&css_set_lock);
2057     hash_for_each(css_set_table, i, cset, hlist) {
2058         link_css_set(&tmp_links, cset, root_cgrp);
2059         if (css_set_populated(cset))
2060             cgroup_update_populated(root_cgrp, true);
2061     }
2062     spin_unlock_irq(&css_set_lock);
2063 
2064     BUG_ON(!list_empty(&root_cgrp->self.children));
2065     BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2066 
2067     kernfs_activate(root_cgrp->kn);
2068     ret = 0;
2069     goto out;
2070 
2071 destroy_root:
2072     kernfs_destroy_root(root->kf_root);
2073     root->kf_root = NULL;
2074 exit_root_id:
2075     cgroup_exit_root_id(root);
2076 cancel_ref:
2077     percpu_ref_exit(&root_cgrp->self.refcnt);
2078 out:
2079     free_cgrp_cset_links(&tmp_links);
2080     return ret;
2081 }
2082 
2083 static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2084              int flags, const char *unused_dev_name,
2085              void *data)
2086 {
2087     bool is_v2 = fs_type == &cgroup2_fs_type;
2088     struct super_block *pinned_sb = NULL;
2089     struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2090     struct cgroup_subsys *ss;
2091     struct cgroup_root *root;
2092     struct cgroup_sb_opts opts;
2093     struct dentry *dentry;
2094     int ret;
2095     int i;
2096     bool new_sb;
2097 
2098     get_cgroup_ns(ns);
2099 
2100     /* Check if the caller has permission to mount. */
2101     if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2102         put_cgroup_ns(ns);
2103         return ERR_PTR(-EPERM);
2104     }
2105 
2106     /*
2107      * The first time anyone tries to mount a cgroup, enable the list
2108      * linking each css_set to its tasks and fix up all existing tasks.
2109      */
2110     if (!use_task_css_set_links)
2111         cgroup_enable_task_cg_lists();
2112 
2113     if (is_v2) {
2114         if (data) {
2115             pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
2116             put_cgroup_ns(ns);
2117             return ERR_PTR(-EINVAL);
2118         }
2119         cgrp_dfl_visible = true;
2120         root = &cgrp_dfl_root;
2121         cgroup_get(&root->cgrp);
2122         goto out_mount;
2123     }
2124 
2125     cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
2126 
2127     /* First find the desired set of subsystems */
2128     ret = parse_cgroupfs_options(data, &opts);
2129     if (ret)
2130         goto out_unlock;
2131 
2132     /*
2133      * Destruction of cgroup root is asynchronous, so subsystems may
2134      * still be dying after the previous unmount.  Let's drain the
2135      * dying subsystems.  We just need to ensure that the ones
2136      * unmounted previously finish dying and don't care about new ones
2137      * starting.  Testing ref liveliness is good enough.
2138      */
2139     for_each_subsys(ss, i) {
2140         if (!(opts.subsys_mask & (1 << i)) ||
2141             ss->root == &cgrp_dfl_root)
2142             continue;
2143 
2144         if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2145             mutex_unlock(&cgroup_mutex);
2146             msleep(10);
2147             ret = restart_syscall();
2148             goto out_free;
2149         }
2150         cgroup_put(&ss->root->cgrp);
2151     }
2152 
2153     for_each_root(root) {
2154         bool name_match = false;
2155 
2156         if (root == &cgrp_dfl_root)
2157             continue;
2158 
2159         /*
2160          * If we asked for a name then it must match.  Also, if
2161          * name matches but sybsys_mask doesn't, we should fail.
2162          * Remember whether name matched.
2163          */
2164         if (opts.name) {
2165             if (strcmp(opts.name, root->name))
2166                 continue;
2167             name_match = true;
2168         }
2169 
2170         /*
2171          * If we asked for subsystems (or explicitly for no
2172          * subsystems) then they must match.
2173          */
2174         if ((opts.subsys_mask || opts.none) &&
2175             (opts.subsys_mask != root->subsys_mask)) {
2176             if (!name_match)
2177                 continue;
2178             ret = -EBUSY;
2179             goto out_unlock;
2180         }
2181 
2182         if (root->flags ^ opts.flags)
2183             pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2184 
2185         /*
2186          * We want to reuse @root whose lifetime is governed by its
2187          * ->cgrp.  Let's check whether @root is alive and keep it
2188          * that way.  As cgroup_kill_sb() can happen anytime, we
2189          * want to block it by pinning the sb so that @root doesn't
2190          * get killed before mount is complete.
2191          *
2192          * With the sb pinned, tryget_live can reliably indicate
2193          * whether @root can be reused.  If it's being killed,
2194          * drain it.  We can use wait_queue for the wait but this
2195          * path is super cold.  Let's just sleep a bit and retry.
2196          */
2197         pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2198         if (IS_ERR(pinned_sb) ||
2199             !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2200             mutex_unlock(&cgroup_mutex);
2201             if (!IS_ERR_OR_NULL(pinned_sb))
2202                 deactivate_super(pinned_sb);
2203             msleep(10);
2204             ret = restart_syscall();
2205             goto out_free;
2206         }
2207 
2208         ret = 0;
2209         goto out_unlock;
2210     }
2211 
2212     /*
2213      * No such thing, create a new one.  name= matching without subsys
2214      * specification is allowed for already existing hierarchies but we
2215      * can't create new one without subsys specification.
2216      */
2217     if (!opts.subsys_mask && !opts.none) {
2218         ret = -EINVAL;
2219         goto out_unlock;
2220     }
2221 
2222     /* Hierarchies may only be created in the initial cgroup namespace. */
2223     if (ns != &init_cgroup_ns) {
2224         ret = -EPERM;
2225         goto out_unlock;
2226     }
2227 
2228     root = kzalloc(sizeof(*root), GFP_KERNEL);
2229     if (!root) {
2230         ret = -ENOMEM;
2231         goto out_unlock;
2232     }
2233 
2234     init_cgroup_root(root, &opts);
2235 
2236     ret = cgroup_setup_root(root, opts.subsys_mask);
2237     if (ret)
2238         cgroup_free_root(root);
2239 
2240 out_unlock:
2241     mutex_unlock(&cgroup_mutex);
2242 out_free:
2243     kfree(opts.release_agent);
2244     kfree(opts.name);
2245 
2246     if (ret) {
2247         put_cgroup_ns(ns);
2248         return ERR_PTR(ret);
2249     }
2250 out_mount:
2251     dentry = kernfs_mount(fs_type, flags, root->kf_root,
2252                   is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2253                   &new_sb);
2254 
2255     /*
2256      * In non-init cgroup namespace, instead of root cgroup's
2257      * dentry, we return the dentry corresponding to the
2258      * cgroupns->root_cgrp.
2259      */
2260     if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
2261         struct dentry *nsdentry;
2262         struct cgroup *cgrp;
2263 
2264         mutex_lock(&cgroup_mutex);
2265         spin_lock_irq(&css_set_lock);
2266 
2267         cgrp = cset_cgroup_from_root(ns->root_cset, root);
2268 
2269         spin_unlock_irq(&css_set_lock);
2270         mutex_unlock(&cgroup_mutex);
2271 
2272         nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2273         dput(dentry);
2274         dentry = nsdentry;
2275     }
2276 
2277     if (IS_ERR(dentry) || !new_sb)
2278         cgroup_put(&root->cgrp);
2279 
2280     /*
2281      * If @pinned_sb, we're reusing an existing root and holding an
2282      * extra ref on its sb.  Mount is complete.  Put the extra ref.
2283      */
2284     if (pinned_sb) {
2285         WARN_ON(new_sb);
2286         deactivate_super(pinned_sb);
2287     }
2288 
2289     put_cgroup_ns(ns);
2290     return dentry;
2291 }
2292 
2293 static void cgroup_kill_sb(struct super_block *sb)
2294 {
2295     struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2296     struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2297 
2298     /*
2299      * If @root doesn't have any mounts or children, start killing it.
2300      * This prevents new mounts by disabling percpu_ref_tryget_live().
2301      * cgroup_mount() may wait for @root's release.
2302      *
2303      * And don't kill the default root.
2304      */
2305     if (!list_empty(&root->cgrp.self.children) ||
2306         root == &cgrp_dfl_root)
2307         cgroup_put(&root->cgrp);
2308     else
2309         percpu_ref_kill(&root->cgrp.self.refcnt);
2310 
2311     kernfs_kill_sb(sb);
2312 }
2313 
2314 static struct file_system_type cgroup_fs_type = {
2315     .name = "cgroup",
2316     .mount = cgroup_mount,
2317     .kill_sb = cgroup_kill_sb,
2318     .fs_flags = FS_USERNS_MOUNT,
2319 };
2320 
2321 static struct file_system_type cgroup2_fs_type = {
2322     .name = "cgroup2",
2323     .mount = cgroup_mount,
2324     .kill_sb = cgroup_kill_sb,
2325     .fs_flags = FS_USERNS_MOUNT,
2326 };
2327 
2328 static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2329                  struct cgroup_namespace *ns)
2330 {
2331     struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2332 
2333     return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2334 }
2335 
2336 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2337            struct cgroup_namespace *ns)
2338 {
2339     int ret;
2340 
2341     mutex_lock(&cgroup_mutex);
2342     spin_lock_irq(&css_set_lock);
2343 
2344     ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2345 
2346     spin_unlock_irq(&css_set_lock);
2347     mutex_unlock(&cgroup_mutex);
2348 
2349     return ret;
2350 }
2351 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2352 
2353 /**
2354  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2355  * @task: target task
2356  * @buf: the buffer to write the path into
2357  * @buflen: the length of the buffer
2358  *
2359  * Determine @task's cgroup on the first (the one with the lowest non-zero
2360  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2361  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2362  * cgroup controller callbacks.
2363  *
2364  * Return value is the same as kernfs_path().
2365  */
2366 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2367 {
2368     struct cgroup_root *root;
2369     struct cgroup *cgrp;
2370     int hierarchy_id = 1;
2371     int ret;
2372 
2373     mutex_lock(&cgroup_mutex);
2374     spin_lock_irq(&css_set_lock);
2375 
2376     root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2377 
2378     if (root) {
2379         cgrp = task_cgroup_from_root(task, root);
2380         ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2381     } else {
2382         /* if no hierarchy exists, everyone is in "/" */
2383         ret = strlcpy(buf, "/", buflen);
2384     }
2385 
2386     spin_unlock_irq(&css_set_lock);
2387     mutex_unlock(&cgroup_mutex);
2388     return ret;
2389 }
2390 EXPORT_SYMBOL_GPL(task_cgroup_path);
2391 
2392 /* used to track tasks and other necessary states during migration */
2393 struct cgroup_taskset {
2394     /* the src and dst cset list running through cset->mg_node */
2395     struct list_head    src_csets;
2396     struct list_head    dst_csets;
2397 
2398     /* the subsys currently being processed */
2399     int         ssid;
2400 
2401     /*
2402      * Fields for cgroup_taskset_*() iteration.
2403      *
2404      * Before migration is committed, the target migration tasks are on
2405      * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
2406      * the csets on ->dst_csets.  ->csets point to either ->src_csets
2407      * or ->dst_csets depending on whether migration is committed.
2408      *
2409      * ->cur_csets and ->cur_task point to the current task position
2410      * during iteration.
2411      */
2412     struct list_head    *csets;
2413     struct css_set      *cur_cset;
2414     struct task_struct  *cur_task;
2415 };
2416 
2417 #define CGROUP_TASKSET_INIT(tset)   (struct cgroup_taskset){    \
2418     .src_csets      = LIST_HEAD_INIT(tset.src_csets),   \
2419     .dst_csets      = LIST_HEAD_INIT(tset.dst_csets),   \
2420     .csets          = &tset.src_csets,          \
2421 }
2422 
2423 /**
2424  * cgroup_taskset_add - try to add a migration target task to a taskset
2425  * @task: target task
2426  * @tset: target taskset
2427  *
2428  * Add @task, which is a migration target, to @tset.  This function becomes
2429  * noop if @task doesn't need to be migrated.  @task's css_set should have
2430  * been added as a migration source and @task->cg_list will be moved from
2431  * the css_set's tasks list to mg_tasks one.
2432  */
2433 static void cgroup_taskset_add(struct task_struct *task,
2434                    struct cgroup_taskset *tset)
2435 {
2436     struct css_set *cset;
2437 
2438     lockdep_assert_held(&css_set_lock);
2439 
2440     /* @task either already exited or can't exit until the end */
2441     if (task->flags & PF_EXITING)
2442         return;
2443 
2444     /* leave @task alone if post_fork() hasn't linked it yet */
2445     if (list_empty(&task->cg_list))
2446         return;
2447 
2448     cset = task_css_set(task);
2449     if (!cset->mg_src_cgrp)
2450         return;
2451 
2452     list_move_tail(&task->cg_list, &cset->mg_tasks);
2453     if (list_empty(&cset->mg_node))
2454         list_add_tail(&cset->mg_node, &tset->src_csets);
2455     if (list_empty(&cset->mg_dst_cset->mg_node))
2456         list_move_tail(&cset->mg_dst_cset->mg_node,
2457                    &tset->dst_csets);
2458 }
2459 
2460 /**
2461  * cgroup_taskset_first - reset taskset and return the first task
2462  * @tset: taskset of interest
2463  * @dst_cssp: output variable for the destination css
2464  *
2465  * @tset iteration is initialized and the first task is returned.
2466  */
2467 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2468                      struct cgroup_subsys_state **dst_cssp)
2469 {
2470     tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2471     tset->cur_task = NULL;
2472 
2473     return cgroup_taskset_next(tset, dst_cssp);
2474 }
2475 
2476 /**
2477  * cgroup_taskset_next - iterate to the next task in taskset
2478  * @tset: taskset of interest
2479  * @dst_cssp: output variable for the destination css
2480  *
2481  * Return the next task in @tset.  Iteration must have been initialized
2482  * with cgroup_taskset_first().
2483  */
2484 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2485                     struct cgroup_subsys_state **dst_cssp)
2486 {
2487     struct css_set *cset = tset->cur_cset;
2488     struct task_struct *task = tset->cur_task;
2489 
2490     while (&cset->mg_node != tset->csets) {
2491         if (!task)
2492             task = list_first_entry(&cset->mg_tasks,
2493                         struct task_struct, cg_list);
2494         else
2495             task = list_next_entry(task, cg_list);
2496 
2497         if (&task->cg_list != &cset->mg_tasks) {
2498             tset->cur_cset = cset;
2499             tset->cur_task = task;
2500 
2501             /*
2502              * This function may be called both before and
2503              * after cgroup_taskset_migrate().  The two cases
2504              * can be distinguished by looking at whether @cset
2505              * has its ->mg_dst_cset set.
2506              */
2507             if (cset->mg_dst_cset)
2508                 *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2509             else
2510                 *dst_cssp = cset->subsys[tset->ssid];
2511 
2512             return task;
2513         }
2514 
2515         cset = list_next_entry(cset, mg_node);
2516         task = NULL;
2517     }
2518 
2519     return NULL;
2520 }
2521 
2522 /**
2523  * cgroup_taskset_migrate - migrate a taskset
2524  * @tset: taget taskset
2525  * @root: cgroup root the migration is taking place on
2526  *
2527  * Migrate tasks in @tset as setup by migration preparation functions.
2528  * This function fails iff one of the ->can_attach callbacks fails and
2529  * guarantees that either all or none of the tasks in @tset are migrated.
2530  * @tset is consumed regardless of success.
2531  */
2532 static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2533                   struct cgroup_root *root)
2534 {
2535     struct cgroup_subsys *ss;
2536     struct task_struct *task, *tmp_task;
2537     struct css_set *cset, *tmp_cset;
2538     int ssid, failed_ssid, ret;
2539 
2540     /* methods shouldn't be called if no task is actually migrating */
2541     if (list_empty(&tset->src_csets))
2542         return 0;
2543 
2544     /* check that we can legitimately attach to the cgroup */
2545     do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2546         if (ss->can_attach) {
2547             tset->ssid = ssid;
2548             ret = ss->can_attach(tset);
2549             if (ret) {
2550                 failed_ssid = ssid;
2551                 goto out_cancel_attach;
2552             }
2553         }
2554     } while_each_subsys_mask();
2555 
2556     /*
2557      * Now that we're guaranteed success, proceed to move all tasks to
2558      * the new cgroup.  There are no failure cases after here, so this
2559      * is the commit point.
2560      */
2561     spin_lock_irq(&css_set_lock);
2562     list_for_each_entry(cset, &tset->src_csets, mg_node) {
2563         list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2564             struct css_set *from_cset = task_css_set(task);
2565             struct css_set *to_cset = cset->mg_dst_cset;
2566 
2567             get_css_set(to_cset);
2568             css_set_move_task(task, from_cset, to_cset, true);
2569             put_css_set_locked(from_cset);
2570         }
2571     }
2572     spin_unlock_irq(&css_set_lock);
2573 
2574     /*
2575      * Migration is committed, all target tasks are now on dst_csets.
2576      * Nothing is sensitive to fork() after this point.  Notify
2577      * controllers that migration is complete.
2578      */
2579     tset->csets = &tset->dst_csets;
2580 
2581     do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2582         if (ss->attach) {
2583             tset->ssid = ssid;
2584             ss->attach(tset);
2585         }
2586     } while_each_subsys_mask();
2587 
2588     ret = 0;
2589     goto out_release_tset;
2590 
2591 out_cancel_attach:
2592     do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2593         if (ssid == failed_ssid)
2594             break;
2595         if (ss->cancel_attach) {
2596             tset->ssid = ssid;
2597             ss->cancel_attach(tset);
2598         }
2599     } while_each_subsys_mask();
2600 out_release_tset:
2601     spin_lock_irq(&css_set_lock);
2602     list_splice_init(&tset->dst_csets, &tset->src_csets);
2603     list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2604         list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2605         list_del_init(&cset->mg_node);
2606     }
2607     spin_unlock_irq(&css_set_lock);
2608     return ret;
2609 }
2610 
2611 /**
2612  * cgroup_may_migrate_to - verify whether a cgroup can be migration destination
2613  * @dst_cgrp: destination cgroup to test
2614  *
2615  * On the default hierarchy, except for the root, subtree_control must be
2616  * zero for migration destination cgroups with tasks so that child cgroups
2617  * don't compete against tasks.
2618  */
2619 static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
2620 {
2621     return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||
2622         !dst_cgrp->subtree_control;
2623 }
2624 
2625 /**
2626  * cgroup_migrate_finish - cleanup after attach
2627  * @preloaded_csets: list of preloaded css_sets
2628  *
2629  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2630  * those functions for details.
2631  */
2632 static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2633 {
2634     struct css_set *cset, *tmp_cset;
2635 
2636     lockdep_assert_held(&cgroup_mutex);
2637 
2638     spin_lock_irq(&css_set_lock);
2639     list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2640         cset->mg_src_cgrp = NULL;
2641         cset->mg_dst_cgrp = NULL;
2642         cset->mg_dst_cset = NULL;
2643         list_del_init(&cset->mg_preload_node);
2644         put_css_set_locked(cset);
2645     }
2646     spin_unlock_irq(&css_set_lock);
2647 }
2648 
2649 /**
2650  * cgroup_migrate_add_src - add a migration source css_set
2651  * @src_cset: the source css_set to add
2652  * @dst_cgrp: the destination cgroup
2653  * @preloaded_csets: list of preloaded css_sets
2654  *
2655  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2656  * @src_cset and add it to @preloaded_csets, which should later be cleaned
2657  * up by cgroup_migrate_finish().
2658  *
2659  * This function may be called without holding cgroup_threadgroup_rwsem
2660  * even if the target is a process.  Threads may be created and destroyed
2661  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2662  * into play and the preloaded css_sets are guaranteed to cover all
2663  * migrations.
2664  */
2665 static void cgroup_migrate_add_src(struct css_set *src_cset,
2666                    struct cgroup *dst_cgrp,
2667                    struct list_head *preloaded_csets)
2668 {
2669     struct cgroup *src_cgrp;
2670 
2671     lockdep_assert_held(&cgroup_mutex);
2672     lockdep_assert_held(&css_set_lock);
2673 
2674     /*
2675      * If ->dead, @src_set is associated with one or more dead cgroups
2676      * and doesn't contain any migratable tasks.  Ignore it early so
2677      * that the rest of migration path doesn't get confused by it.
2678      */
2679     if (src_cset->dead)
2680         return;
2681 
2682     src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2683 
2684     if (!list_empty(&src_cset->mg_preload_node))
2685         return;
2686 
2687     WARN_ON(src_cset->mg_src_cgrp);
2688     WARN_ON(src_cset->mg_dst_cgrp);
2689     WARN_ON(!list_empty(&src_cset->mg_tasks));
2690     WARN_ON(!list_empty(&src_cset->mg_node));
2691 
2692     src_cset->mg_src_cgrp = src_cgrp;
2693     src_cset->mg_dst_cgrp = dst_cgrp;
2694     get_css_set(src_cset);
2695     list_add(&src_cset->mg_preload_node, preloaded_csets);
2696 }
2697 
2698 /**
2699  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2700  * @preloaded_csets: list of preloaded source css_sets
2701  *
2702  * Tasks are about to be moved and all the source css_sets have been
2703  * preloaded to @preloaded_csets.  This function looks up and pins all
2704  * destination css_sets, links each to its source, and append them to
2705  * @preloaded_csets.
2706  *
2707  * This function must be called after cgroup_migrate_add_src() has been
2708  * called on each migration source css_set.  After migration is performed
2709  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2710  * @preloaded_csets.
2711  */
2712 static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
2713 {
2714     LIST_HEAD(csets);
2715     struct css_set *src_cset, *tmp_cset;
2716 
2717     lockdep_assert_held(&cgroup_mutex);
2718 
2719     /* look up the dst cset for each src cset and link it to src */
2720     list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2721         struct css_set *dst_cset;
2722 
2723         dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2724         if (!dst_cset)
2725             goto err;
2726 
2727         WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2728 
2729         /*
2730          * If src cset equals dst, it's noop.  Drop the src.
2731          * cgroup_migrate() will skip the cset too.  Note that we
2732          * can't handle src == dst as some nodes are used by both.
2733          */
2734         if (src_cset == dst_cset) {
2735             src_cset->mg_src_cgrp = NULL;
2736             src_cset->mg_dst_cgrp = NULL;
2737             list_del_init(&src_cset->mg_preload_node);
2738             put_css_set(src_cset);
2739             put_css_set(dst_cset);
2740             continue;
2741         }
2742 
2743         src_cset->mg_dst_cset = dst_cset;
2744 
2745         if (list_empty(&dst_cset->mg_preload_node))
2746             list_add(&dst_cset->mg_preload_node, &csets);
2747         else
2748             put_css_set(dst_cset);
2749     }
2750 
2751     list_splice_tail(&csets, preloaded_csets);
2752     return 0;
2753 err:
2754     cgroup_migrate_finish(&csets);
2755     return -ENOMEM;
2756 }
2757 
2758 /**
2759  * cgroup_migrate - migrate a process or task to a cgroup
2760  * @leader: the leader of the process or the task to migrate
2761  * @threadgroup: whether @leader points to the whole process or a single task
2762  * @root: cgroup root migration is taking place on
2763  *
2764  * Migrate a process or task denoted by @leader.  If migrating a process,
2765  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2766  * responsible for invoking cgroup_migrate_add_src() and
2767  * cgroup_migrate_prepare_dst() on the targets before invoking this
2768  * function and following up with cgroup_migrate_finish().
2769  *
2770  * As long as a controller's ->can_attach() doesn't fail, this function is
2771  * guaranteed to succeed.  This means that, excluding ->can_attach()
2772  * failure, when migrating multiple targets, the success or failure can be
2773  * decided for all targets by invoking group_migrate_prepare_dst() before
2774  * actually starting migrating.
2775  */
2776 static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2777               struct cgroup_root *root)
2778 {
2779     struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2780     struct task_struct *task;
2781 
2782     /*
2783      * Prevent freeing of tasks while we take a snapshot. Tasks that are
2784      * already PF_EXITING could be freed from underneath us unless we
2785      * take an rcu_read_lock.
2786      */
2787     spin_lock_irq(&css_set_lock);
2788     rcu_read_lock();
2789     task = leader;
2790     do {
2791         cgroup_taskset_add(task, &tset);
2792         if (!threadgroup)
2793             break;
2794     } while_each_thread(leader, task);
2795     rcu_read_unlock();
2796     spin_unlock_irq(&css_set_lock);
2797 
2798     return cgroup_taskset_migrate(&tset, root);
2799 }
2800 
2801 /**
2802  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2803  * @dst_cgrp: the cgroup to attach to
2804  * @leader: the task or the leader of the threadgroup to be attached
2805  * @threadgroup: attach the whole threadgroup?
2806  *
2807  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2808  */
2809 static int cgroup_attach_task(struct cgroup *dst_cgrp,
2810                   struct task_struct *leader, bool threadgroup)
2811 {
2812     LIST_HEAD(preloaded_csets);
2813     struct task_struct *task;
2814     int ret;
2815 
2816     if (!cgroup_may_migrate_to(dst_cgrp))
2817         return -EBUSY;
2818 
2819     /* look up all src csets */
2820     spin_lock_irq(&css_set_lock);
2821     rcu_read_lock();
2822     task = leader;
2823     do {
2824         cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2825                        &preloaded_csets);
2826         if (!threadgroup)
2827             break;
2828     } while_each_thread(leader, task);
2829     rcu_read_unlock();
2830     spin_unlock_irq(&css_set_lock);
2831 
2832     /* prepare dst csets and commit */
2833     ret = cgroup_migrate_prepare_dst(&preloaded_csets);
2834     if (!ret)
2835         ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
2836 
2837     cgroup_migrate_finish(&preloaded_csets);
2838 
2839     if (!ret)
2840         trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
2841 
2842     return ret;
2843 }
2844 
2845 static int cgroup_procs_write_permission(struct task_struct *task,
2846                      struct cgroup *dst_cgrp,
2847                      struct kernfs_open_file *of)
2848 {
2849     const struct cred *cred = current_cred();
2850     const struct cred *tcred = get_task_cred(task);
2851     int ret = 0;
2852 
2853     /*
2854      * even if we're attaching all tasks in the thread group, we only
2855      * need to check permissions on one of them.
2856      */
2857     if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2858         !uid_eq(cred->euid, tcred->uid) &&
2859         !uid_eq(cred->euid, tcred->suid))
2860         ret = -EACCES;
2861 
2862     if (!ret && cgroup_on_dfl(dst_cgrp)) {
2863         struct super_block *sb = of->file->f_path.dentry->d_sb;
2864         struct cgroup *cgrp;
2865         struct inode *inode;
2866 
2867         spin_lock_irq(&css_set_lock);
2868         cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2869         spin_unlock_irq(&css_set_lock);
2870 
2871         while (!cgroup_is_descendant(dst_cgrp, cgrp))
2872             cgrp = cgroup_parent(cgrp);
2873 
2874         ret = -ENOMEM;
2875         inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2876         if (inode) {
2877             ret = inode_permission(inode, MAY_WRITE);
2878             iput(inode);
2879         }
2880     }
2881 
2882     put_cred(tcred);
2883     return ret;
2884 }
2885 
2886 /*
2887  * Find the task_struct of the task to attach by vpid and pass it along to the
2888  * function to attach either it or all tasks in its threadgroup. Will lock
2889  * cgroup_mutex and threadgroup.
2890  */
2891 static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
2892                     size_t nbytes, loff_t off, bool threadgroup)
2893 {
2894     struct task_struct *tsk;
2895     struct cgroup_subsys *ss;
2896     struct cgroup *cgrp;
2897     pid_t pid;
2898     int ssid, ret;
2899 
2900     if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2901         return -EINVAL;
2902 
2903     cgrp = cgroup_kn_lock_live(of->kn, false);
2904     if (!cgrp)
2905         return -ENODEV;
2906 
2907     percpu_down_write(&cgroup_threadgroup_rwsem);
2908     rcu_read_lock();
2909     if (pid) {
2910         tsk = find_task_by_vpid(pid);
2911         if (!tsk) {
2912             ret = -ESRCH;
2913             goto out_unlock_rcu;
2914         }
2915     } else {
2916         tsk = current;
2917     }
2918 
2919     if (threadgroup)
2920         tsk = tsk->group_leader;
2921 
2922     /*
2923      * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2924      * trapped in a cpuset, or RT worker may be born in a cgroup
2925      * with no rt_runtime allocated.  Just say no.
2926      */
2927     if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2928         ret = -EINVAL;
2929         goto out_unlock_rcu;
2930     }
2931 
2932     get_task_struct(tsk);
2933     rcu_read_unlock();
2934 
2935     ret = cgroup_procs_write_permission(tsk, cgrp, of);
2936     if (!ret)
2937         ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2938 
2939     put_task_struct(tsk);
2940     goto out_unlock_threadgroup;
2941 
2942 out_unlock_rcu:
2943     rcu_read_unlock();
2944 out_unlock_threadgroup:
2945     percpu_up_write(&cgroup_threadgroup_rwsem);
2946     for_each_subsys(ss, ssid)
2947         if (ss->post_attach)
2948             ss->post_attach();
2949     cgroup_kn_unlock(of->kn);
2950     return ret ?: nbytes;
2951 }
2952 
2953 /**
2954  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2955  * @from: attach to all cgroups of a given task
2956  * @tsk: the task to be attached
2957  */
2958 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2959 {
2960     struct cgroup_root *root;
2961     int retval = 0;
2962 
2963     mutex_lock(&cgroup_mutex);
2964     percpu_down_write(&cgroup_threadgroup_rwsem);
2965     for_each_root(root) {
2966         struct cgroup *from_cgrp;
2967 
2968         if (root == &cgrp_dfl_root)
2969             continue;
2970 
2971         spin_lock_irq(&css_set_lock);
2972         from_cgrp = task_cgroup_from_root(from, root);
2973         spin_unlock_irq(&css_set_lock);
2974 
2975         retval = cgroup_attach_task(from_cgrp, tsk, false);
2976         if (retval)
2977             break;
2978     }
2979     percpu_up_write(&cgroup_threadgroup_rwsem);
2980     mutex_unlock(&cgroup_mutex);
2981 
2982     return retval;
2983 }
2984 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2985 
2986 static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2987                   char *buf, size_t nbytes, loff_t off)
2988 {
2989     return __cgroup_procs_write(of, buf, nbytes, off, false);
2990 }
2991 
2992 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2993                   char *buf, size_t nbytes, loff_t off)
2994 {
2995     return __cgroup_procs_write(of, buf, nbytes, off, true);
2996 }
2997 
2998 static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2999                       char *buf, size_t nbytes, loff_t off)
3000 {
3001     struct cgroup *cgrp;
3002 
3003     BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
3004 
3005     cgrp = cgroup_kn_lock_live(of->kn, false);
3006     if (!cgrp)
3007         return -ENODEV;
3008     spin_lock(&release_agent_path_lock);
3009     strlcpy(cgrp->root->release_agent_path, strstrip(buf),
3010         sizeof(cgrp->root->release_agent_path));
3011     spin_unlock(&release_agent_path_lock);
3012     cgroup_kn_unlock(of->kn);
3013     return nbytes;
3014 }
3015 
3016 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
3017 {
3018     struct cgroup *cgrp = seq_css(seq)->cgroup;
3019 
3020     spin_lock(&release_agent_path_lock);
3021     seq_puts(seq, cgrp->root->release_agent_path);
3022     spin_unlock(&release_agent_path_lock);
3023     seq_putc(seq, '\n');
3024     return 0;
3025 }
3026 
3027 static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
3028 {
3029     seq_puts(seq, "0\n");
3030     return 0;
3031 }
3032 
3033 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
3034 {
3035     struct cgroup_subsys *ss;
3036     bool printed = false;
3037     int ssid;
3038 
3039     do_each_subsys_mask(ss, ssid, ss_mask) {
3040         if (printed)
3041             seq_putc(seq, ' ');
3042         seq_printf(seq, "%s", ss->name);
3043         printed = true;
3044     } while_each_subsys_mask();
3045     if (printed)
3046         seq_putc(seq, '\n');
3047 }
3048 
3049 /* show controllers which are enabled from the parent */
3050 static int cgroup_controllers_show(struct seq_file *seq, void *v)
3051 {
3052     struct cgroup *cgrp = seq_css(seq)->cgroup;
3053 
3054     cgroup_print_ss_mask(seq, cgroup_control(cgrp));
3055     return 0;
3056 }
3057 
3058 /* show controllers which are enabled for a given cgroup's children */
3059 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
3060 {
3061     struct cgroup *cgrp = seq_css(seq)->cgroup;
3062 
3063     cgroup_print_ss_mask(seq, cgrp->subtree_control);
3064     return 0;
3065 }
3066 
3067 /**
3068  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
3069  * @cgrp: root of the subtree to update csses for
3070  *
3071  * @cgrp's control masks have changed and its subtree's css associations
3072  * need to be updated accordingly.  This function looks up all css_sets
3073  * which are attached to the subtree, creates the matching updated css_sets
3074  * and migrates the tasks to the new ones.
3075  */
3076 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
3077 {
3078     LIST_HEAD(preloaded_csets);
3079     struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
3080     struct cgroup_subsys_state *d_css;
3081     struct cgroup *dsct;
3082     struct css_set *src_cset;
3083     int ret;
3084 
3085     lockdep_assert_held(&cgroup_mutex);
3086 
3087     percpu_down_write(&cgroup_threadgroup_rwsem);
3088 
3089     /* look up all csses currently attached to @cgrp's subtree */
3090     spin_lock_irq(&css_set_lock);
3091     cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3092         struct cgrp_cset_link *link;
3093 
3094         list_for_each_entry(link, &dsct->cset_links, cset_link)
3095             cgroup_migrate_add_src(link->cset, dsct,
3096                            &preloaded_csets);
3097     }
3098     spin_unlock_irq(&css_set_lock);
3099 
3100     /* NULL dst indicates self on default hierarchy */
3101     ret = cgroup_migrate_prepare_dst(&preloaded_csets);
3102     if (ret)
3103         goto out_finish;
3104 
3105     spin_lock_irq(&css_set_lock);
3106     list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
3107         struct task_struct *task, *ntask;
3108 
3109         /* src_csets precede dst_csets, break on the first dst_cset */
3110         if (!src_cset->mg_src_cgrp)
3111             break;
3112 
3113         /* all tasks in src_csets need to be migrated */
3114         list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
3115             cgroup_taskset_add(task, &tset);
3116     }
3117     spin_unlock_irq(&css_set_lock);
3118 
3119     ret = cgroup_taskset_migrate(&tset, cgrp->root);
3120 out_finish:
3121     cgroup_migrate_finish(&preloaded_csets);
3122     percpu_up_write(&cgroup_threadgroup_rwsem);
3123     return ret;
3124 }
3125 
3126 /**
3127  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
3128  * @cgrp: root of the target subtree
3129  *
3130  * Because css offlining is asynchronous, userland may try to re-enable a
3131  * controller while the previous css is still around.  This function grabs
3132  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
3133  */
3134 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
3135     __acquires(&cgroup_mutex)
3136 {
3137     struct cgroup *dsct;
3138     struct cgroup_subsys_state *d_css;
3139     struct cgroup_subsys *ss;
3140     int ssid;
3141 
3142 restart:
3143     mutex_lock(&cgroup_mutex);
3144 
3145     cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3146         for_each_subsys(ss, ssid) {
3147             struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3148             DEFINE_WAIT(wait);
3149 
3150             if (!css || !percpu_ref_is_dying(&css->refcnt))
3151                 continue;
3152 
3153             cgroup_get(dsct);
3154             prepare_to_wait(&dsct->offline_waitq, &wait,
3155                     TASK_UNINTERRUPTIBLE);
3156 
3157             mutex_unlock(&cgroup_mutex);
3158             schedule();
3159             finish_wait(&dsct->offline_waitq, &wait);
3160 
3161             cgroup_put(dsct);
3162             goto restart;
3163         }
3164     }
3165 }
3166 
3167 /**
3168  * cgroup_save_control - save control masks of a subtree
3169  * @cgrp: root of the target subtree
3170  *
3171  * Save ->subtree_control and ->subtree_ss_mask to the respective old_
3172  * prefixed fields for @cgrp's subtree including @cgrp itself.
3173  */
3174 static void cgroup_save_control(struct cgroup *cgrp)
3175 {
3176     struct cgroup *dsct;
3177     struct cgroup_subsys_state *d_css;
3178 
3179     cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3180         dsct->old_subtree_control = dsct->subtree_control;
3181         dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3182     }
3183 }
3184 
3185 /**
3186  * cgroup_propagate_control - refresh control masks of a subtree
3187  * @cgrp: root of the target subtree
3188  *
3189  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3190  * ->subtree_control and propagate controller availability through the
3191  * subtree so that descendants don't have unavailable controllers enabled.
3192  */
3193 static void cgroup_propagate_control(struct cgroup *cgrp)
3194 {
3195     struct cgroup *dsct;
3196     struct cgroup_subsys_state *d_css;
3197 
3198     cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3199         dsct->subtree_control &= cgroup_control(dsct);
3200         dsct->subtree_ss_mask =
3201             cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3202                             cgroup_ss_mask(dsct));
3203     }
3204 }
3205 
3206 /**
3207  * cgroup_restore_control - restore control masks of a subtree
3208  * @cgrp: root of the target subtree
3209  *
3210  * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
3211  * prefixed fields for @cgrp's subtree including @cgrp itself.
3212  */
3213 static void cgroup_restore_control(struct cgroup *cgrp)
3214 {
3215     struct cgroup *dsct;
3216     struct cgroup_subsys_state *d_css;
3217 
3218     cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3219         dsct->subtree_control = dsct->old_subtree_control;
3220         dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3221     }
3222 }
3223 
3224 static bool css_visible(struct cgroup_subsys_state *css)
3225 {
3226     struct cgroup_subsys *ss = css->ss;
3227     struct cgroup *cgrp = css->cgroup;
3228 
3229     if (cgroup_control(cgrp) & (1 << ss->id))
3230         return true;
3231     if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3232         return false;
3233     return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3234 }
3235 
3236 /**
3237  * cgroup_apply_control_enable - enable or show csses according to control
3238  * @cgrp: root of the target subtree
3239  *
3240  * Walk @cgrp's subtree and create new csses or make the existing ones
3241  * visible.  A css is created invisible if it's being implicitly enabled
3242  * through dependency.  An invisible css is made visible when the userland
3243  * explicitly enables it.
3244  *
3245  * Returns 0 on success, -errno on failure.  On failure, csses which have
3246  * been processed already aren't cleaned up.  The caller is responsible for
3247  * cleaning up with cgroup_apply_control_disble().
3248  */
3249 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3250 {
3251     struct cgroup *dsct;
3252     struct cgroup_subsys_state *d_css;
3253     struct cgroup_subsys *ss;
3254     int ssid, ret;
3255 
3256     cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3257         for_each_subsys(ss, ssid) {
3258             struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3259 
3260             WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3261 
3262             if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3263                 continue;
3264 
3265             if (!css) {
3266                 css = css_create(dsct, ss);
3267                 if (IS_ERR(css))
3268                     return PTR_ERR(css);
3269             }
3270 
3271             if (css_visible(css)) {
3272                 ret = css_populate_dir(css);
3273                 if (ret)
3274                     return ret;
3275             }
3276         }
3277     }
3278 
3279     return 0;
3280 }
3281 
3282 /**
3283  * cgroup_apply_control_disable - kill or hide csses according to control
3284  * @cgrp: root of the target subtree
3285  *
3286  * Walk @cgrp's subtree and kill and hide csses so that they match
3287  * cgroup_ss_mask() and cgroup_visible_mask().
3288  *
3289  * A css is hidden when the userland requests it to be disabled while other
3290  * subsystems are still depending on it.  The css must not actively control
3291  * resources and be in the vanilla state if it's made visible again later.
3292  * Controllers which may be depended upon should provide ->css_reset() for
3293  * this purpose.
3294  */
3295 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3296 {
3297     struct cgroup *dsct;
3298     struct cgroup_subsys_state *d_css;
3299     struct cgroup_subsys *ss;
3300     int ssid;
3301 
3302     cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3303         for_each_subsys(ss, ssid) {
3304             struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3305 
3306             WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3307 
3308             if (!css)
3309                 continue;
3310 
3311             if (css->parent &&
3312                 !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3313                 kill_css(css);
3314             } else if (!css_visible(css)) {
3315                 css_clear_dir(css);
3316                 if (ss->css_reset)
3317                     ss->css_reset(css);
3318             }
3319         }
3320     }
3321 }
3322 
3323 /**
3324  * cgroup_apply_control - apply control mask updates to the subtree
3325  * @cgrp: root of the target subtree
3326  *
3327  * subsystems can be enabled and disabled in a subtree using the following
3328  * steps.
3329  *
3330  * 1. Call cgroup_save_control() to stash the current state.
3331  * 2. Update ->subtree_control masks in the subtree as desired.
3332  * 3. Call cgroup_apply_control() to apply the changes.
3333  * 4. Optionally perform other related operations.
3334  * 5. Call cgroup_finalize_control() to finish up.
3335  *
3336  * This function implements step 3 and propagates the mask changes
3337  * throughout @cgrp's subtree, updates csses accordingly and perform
3338  * process migrations.
3339  */
3340 static int cgroup_apply_control(struct cgroup *cgrp)
3341 {
3342     int ret;
3343 
3344     cgroup_propagate_control(cgrp);
3345 
3346     ret = cgroup_apply_control_enable(cgrp);
3347     if (ret)
3348         return ret;
3349 
3350     /*
3351      * At this point, cgroup_e_css() results reflect the new csses
3352      * making the following cgroup_update_dfl_csses() properly update
3353      * css associations of all tasks in the subtree.
3354      */
3355     ret = cgroup_update_dfl_csses(cgrp);
3356     if (ret)
3357         return ret;
3358 
3359     return 0;
3360 }
3361 
3362 /**
3363  * cgroup_finalize_control - finalize control mask update
3364  * @cgrp: root of the target subtree
3365  * @ret: the result of the update
3366  *
3367  * Finalize control mask update.  See cgroup_apply_control() for more info.
3368  */
3369 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3370 {
3371     if (ret) {
3372         cgroup_restore_control(cgrp);
3373         cgroup_propagate_control(cgrp);
3374     }
3375 
3376     cgroup_apply_control_disable(cgrp);
3377 }
3378 
3379 /* change the enabled child controllers for a cgroup in the default hierarchy */
3380 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3381                         char *buf, size_t nbytes,
3382                         loff_t off)
3383 {
3384     u16 enable = 0, disable = 0;
3385     struct cgroup *cgrp, *child;
3386     struct cgroup_subsys *ss;
3387     char *tok;
3388     int ssid, ret;
3389 
3390     /*
3391      * Parse input - space separated list of subsystem names prefixed
3392      * with either + or -.
3393      */
3394     buf = strstrip(buf);
3395     while ((tok = strsep(&buf, " "))) {
3396         if (tok[0] == '\0')
3397             continue;
3398         do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3399             if (!cgroup_ssid_enabled(ssid) ||
3400                 strcmp(tok + 1, ss->name))
3401                 continue;
3402 
3403             if (*tok == '+') {
3404                 enable |= 1 << ssid;
3405                 disable &= ~(1 << ssid);
3406             } else if (*tok == '-') {
3407                 disable |= 1 << ssid;
3408                 enable &= ~(1 << ssid);
3409             } else {
3410                 return -EINVAL;
3411             }
3412             break;
3413         } while_each_subsys_mask();
3414         if (ssid == CGROUP_SUBSYS_COUNT)
3415             return -EINVAL;
3416     }
3417 
3418     cgrp = cgroup_kn_lock_live(of->kn, true);
3419     if (!cgrp)
3420         return -ENODEV;
3421 
3422     for_each_subsys(ss, ssid) {
3423         if (enable & (1 << ssid)) {
3424             if (cgrp->subtree_control & (1 << ssid)) {
3425                 enable &= ~(1 << ssid);
3426                 continue;
3427             }
3428 
3429             if (!(cgroup_control(cgrp) & (1 << ssid))) {
3430                 ret = -ENOENT;
3431                 goto out_unlock;
3432             }
3433         } else if (disable & (1 << ssid)) {
3434             if (!(cgrp->subtree_control & (1 << ssid))) {
3435                 disable &= ~(1 << ssid);
3436                 continue;
3437             }
3438 
3439             /* a child has it enabled? */
3440             cgroup_for_each_live_child(child, cgrp) {
3441                 if (child->subtree_control & (1 << ssid)) {
3442                     ret = -EBUSY;
3443                     goto out_unlock;
3444                 }
3445             }
3446         }
3447     }
3448 
3449     if (!enable && !disable) {
3450         ret = 0;
3451         goto out_unlock;
3452     }
3453 
3454     /*
3455      * Except for the root, subtree_control must be zero for a cgroup
3456      * with tasks so that child cgroups don't compete against tasks.
3457      */
3458     if (enable && cgroup_parent(cgrp)) {
3459         struct cgrp_cset_link *link;
3460 
3461         /*
3462          * Because namespaces pin csets too, @cgrp->cset_links
3463          * might not be empty even when @cgrp is empty.  Walk and
3464          * verify each cset.
3465          */
3466         spin_lock_irq(&css_set_lock);
3467 
3468         ret = 0;
3469         list_for_each_entry(link, &cgrp->cset_links, cset_link) {
3470             if (css_set_populated(link->cset)) {
3471                 ret = -EBUSY;
3472                 break;
3473             }
3474         }
3475 
3476         spin_unlock_irq(&css_set_lock);
3477 
3478         if (ret)
3479             goto out_unlock;
3480     }
3481 
3482     /* save and update control masks and prepare csses */
3483     cgroup_save_control(cgrp);
3484 
3485     cgrp->subtree_control |= enable;
3486     cgrp->subtree_control &= ~disable;
3487 
3488     ret = cgroup_apply_control(cgrp);
3489 
3490     cgroup_finalize_control(cgrp, ret);
3491 
3492     kernfs_activate(cgrp->kn);
3493     ret = 0;
3494 out_unlock:
3495     cgroup_kn_unlock(of->kn);
3496     return ret ?: nbytes;
3497 }
3498 
3499 static int cgroup_events_show(struct seq_file *seq, void *v)
3500 {
3501     seq_printf(seq, "populated %d\n",
3502            cgroup_is_populated(seq_css(seq)->cgroup));
3503     return 0;
3504 }
3505 
3506 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3507                  size_t nbytes, loff_t off)
3508 {
3509     struct cgroup *cgrp = of->kn->parent->priv;
3510     struct cftype *cft = of->kn->priv;
3511     struct cgroup_subsys_state *css;
3512     int ret;
3513 
3514     if (cft->write)
3515         return cft->write(of, buf, nbytes, off);
3516 
3517     /*
3518      * kernfs guarantees that a file isn't deleted with operations in
3519      * flight, which means that the matching css is and stays alive and
3520      * doesn't need to be pinned.  The RCU locking is not necessary
3521      * either.  It's just for the convenience of using cgroup_css().
3522      */
3523     rcu_read_lock();
3524     css = cgroup_css(cgrp, cft->ss);
3525     rcu_read_unlock();
3526 
3527     if (cft->write_u64) {
3528         unsigned long long v;
3529         ret = kstrtoull(buf, 0, &v);
3530         if (!ret)
3531             ret = cft->write_u64(css, cft, v);
3532     } else if (cft->write_s64) {
3533         long long v;
3534         ret = kstrtoll(buf, 0, &v);
3535         if (!ret)
3536             ret = cft->write_s64(css, cft, v);
3537     } else {
3538         ret = -EINVAL;
3539     }
3540 
3541     return ret ?: nbytes;
3542 }
3543 
3544 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3545 {
3546     return seq_cft(seq)->seq_start(seq, ppos);
3547 }
3548 
3549 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3550 {
3551     return seq_cft(seq)->seq_next(seq, v, ppos);
3552 }
3553 
3554 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3555 {
3556     seq_cft(seq)->seq_stop(seq, v);
3557 }
3558 
3559 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3560 {
3561     struct cftype *cft = seq_cft(m);
3562     struct cgroup_subsys_state *css = seq_css(m);
3563 
3564     if (cft->seq_show)
3565         return cft->seq_show(m, arg);
3566 
3567     if (cft->read_u64)
3568         seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3569     else if (cft->read_s64)
3570         seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3571     else
3572         return -EINVAL;
3573     return 0;
3574 }
3575 
3576 static struct kernfs_ops cgroup_kf_single_ops = {
3577     .atomic_write_len   = PAGE_SIZE,
3578     .write          = cgroup_file_write,
3579     .seq_show       = cgroup_seqfile_show,
3580 };
3581 
3582 static struct kernfs_ops cgroup_kf_ops = {
3583     .atomic_write_len   = PAGE_SIZE,
3584     .write          = cgroup_file_write,
3585     .seq_start      = cgroup_seqfile_start,
3586     .seq_next       = cgroup_seqfile_next,
3587     .seq_stop       = cgroup_seqfile_stop,
3588     .seq_show       = cgroup_seqfile_show,
3589 };
3590 
3591 /*
3592  * cgroup_rename - Only allow simple rename of directories in place.
3593  */
3594 static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
3595              const char *new_name_str)
3596 {
3597     struct cgroup *cgrp = kn->priv;
3598     int ret;
3599 
3600     if (kernfs_type(kn) != KERNFS_DIR)
3601         return -ENOTDIR;
3602     if (kn->parent != new_parent)
3603         return -EIO;
3604 
3605     /*
3606      * This isn't a proper migration and its usefulness is very
3607      * limited.  Disallow on the default hierarchy.
3608      */
3609     if (cgroup_on_dfl(cgrp))
3610         return -EPERM;
3611 
3612     /*
3613      * We're gonna grab cgroup_mutex which nests outside kernfs
3614      * active_ref.  kernfs_rename() doesn't require active_ref
3615      * protection.  Break them before grabbing cgroup_mutex.
3616      */
3617     kernfs_break_active_protection(new_parent);
3618     kernfs_break_active_protection(kn);
3619 
3620     mutex_lock(&cgroup_mutex);
3621 
3622     ret = kernfs_rename(kn, new_parent, new_name_str);
3623     if (!ret)
3624         trace_cgroup_rename(cgrp);
3625 
3626     mutex_unlock(&cgroup_mutex);
3627 
3628     kernfs_unbreak_active_protection(kn);
3629     kernfs_unbreak_active_protection(new_parent);
3630     return ret;
3631 }
3632 
3633 /* set uid and gid of cgroup dirs and files to that of the creator */
3634 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3635 {
3636     struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3637                    .ia_uid = current_fsuid(),
3638                    .ia_gid = current_fsgid(), };
3639 
3640     if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3641         gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3642         return 0;
3643 
3644     return kernfs_setattr(kn, &iattr);
3645 }
3646 
3647 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3648                struct cftype *cft)
3649 {
3650     char name[CGROUP_FILE_NAME_MAX];
3651     struct kernfs_node *kn;
3652     struct lock_class_key *key = NULL;
3653     int ret;
3654 
3655 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3656     key = &cft->lockdep_key;
3657 #endif
3658     kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3659                   cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3660                   NULL, key);
3661     if (IS_ERR(kn))
3662         return PTR_ERR(kn);
3663 
3664     ret = cgroup_kn_set_ugid(kn);
3665     if (ret) {
3666         kernfs_remove(kn);
3667         return ret;
3668     }
3669 
3670     if (cft->file_offset) {
3671         struct cgroup_file *cfile = (void *)css + cft->file_offset;
3672 
3673         spin_lock_irq(&cgroup_file_kn_lock);
3674         cfile->kn = kn;
3675         spin_unlock_irq(&cgroup_file_kn_lock);
3676     }
3677 
3678     return 0;
3679 }
3680 
3681 /**
3682  * cgroup_addrm_files - add or remove files to a cgroup directory
3683  * @css: the target css
3684  * @cgrp: the target cgroup (usually css->cgroup)
3685  * @cfts: array of cftypes to be added
3686  * @is_add: whether to add or remove
3687  *
3688  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3689  * For removals, this function never fails.
3690  */
3691 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3692                   struct cgroup *cgrp, struct cftype cfts[],
3693                   bool is_add)
3694 {
3695     struct cftype *cft, *cft_end = NULL;
3696     int ret = 0;
3697 
3698     lockdep_assert_held(&cgroup_mutex);
3699 
3700 restart:
3701     for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3702         /* does cft->flags tell us to skip this file on @cgrp? */
3703         if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3704             continue;
3705         if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3706             continue;
3707         if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3708             continue;
3709         if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3710             continue;
3711 
3712         if (is_add) {
3713             ret = cgroup_add_file(css, cgrp, cft);
3714             if (ret) {
3715                 pr_warn("%s: failed to add %s, err=%d\n",
3716                     __func__, cft->name, ret);
3717                 cft_end = cft;
3718                 is_add = false;
3719                 goto restart;
3720             }
3721         } else {
3722             cgroup_rm_file(cgrp, cft);
3723         }
3724     }
3725     return ret;
3726 }
3727 
3728 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3729 {
3730     LIST_HEAD(pending);
3731     struct cgroup_subsys *ss = cfts[0].ss;
3732     struct cgroup *root = &ss->root->cgrp;
3733     struct cgroup_subsys_state *css;
3734     int ret = 0;
3735 
3736     lockdep_assert_held(&cgroup_mutex);
3737 
3738     /* add/rm files for all cgroups created before */
3739     css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3740         struct cgroup *cgrp = css->cgroup;
3741 
3742         if (!(css->flags & CSS_VISIBLE))
3743             continue;
3744 
3745         ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3746         if (ret)
3747             break;
3748     }
3749 
3750     if (is_add && !ret)
3751         kernfs_activate(root->kn);
3752     return ret;
3753 }
3754 
3755 static void cgroup_exit_cftypes(struct cftype *cfts)
3756 {
3757     struct cftype *cft;
3758 
3759     for (cft = cfts; cft->name[0] != '\0'; cft++) {
3760         /* free copy for custom atomic_write_len, see init_cftypes() */
3761         if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3762             kfree(cft->kf_ops);
3763         cft->kf_ops = NULL;
3764         cft->ss = NULL;
3765 
3766         /* revert flags set by cgroup core while adding @cfts */
3767         cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3768     }
3769 }
3770 
3771 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3772 {
3773     struct cftype *cft;
3774 
3775     for (cft = cfts; cft->name[0] != '\0'; cft++) {
3776         struct kernfs_ops *kf_ops;
3777 
3778         WARN_ON(cft->ss || cft->kf_ops);
3779 
3780         if (cft->seq_start)
3781             kf_ops = &cgroup_kf_ops;
3782         else
3783             kf_ops = &cgroup_kf_single_ops;
3784 
3785         /*
3786          * Ugh... if @cft wants a custom max_write_len, we need to
3787          * make a copy of kf_ops to set its atomic_write_len.
3788          */
3789         if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3790             kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3791             if (!kf_ops) {
3792                 cgroup_exit_cftypes(cfts);
3793                 return -ENOMEM;
3794             }
3795             kf_ops->atomic_write_len = cft->max_write_len;
3796         }
3797 
3798         cft->kf_ops = kf_ops;
3799         cft->ss = ss;
3800     }
3801 
3802     return 0;
3803 }
3804 
3805 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3806 {
3807     lockdep_assert_held(&cgroup_mutex);
3808 
3809     if (!cfts || !cfts[0].ss)
3810         return -ENOENT;
3811 
3812     list_del(&cfts->node);
3813     cgroup_apply_cftypes(cfts, false);
3814     cgroup_exit_cftypes(cfts);
3815     return 0;
3816 }
3817 
3818 /**
3819  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3820  * @cfts: zero-length name terminated array of cftypes
3821  *
3822  * Unregister @cfts.  Files described by @cfts are removed from all
3823  * existing cgroups and all future cgroups won't have them either.  This
3824  * function can be called anytime whether @cfts' subsys is attached or not.
3825  *
3826  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3827  * registered.
3828  */
3829 int cgroup_rm_cftypes(struct cftype *cfts)
3830 {
3831     int ret;
3832 
3833     mutex_lock(&cgroup_mutex);
3834     ret = cgroup_rm_cftypes_locked(cfts);
3835     mutex_unlock(&cgroup_mutex);
3836     return ret;
3837 }
3838 
3839 /**
3840  * cgroup_add_cftypes - add an array of cftypes to a subsystem
3841  * @ss: target cgroup subsystem
3842  * @cfts: zero-length name terminated array of cftypes
3843  *
3844  * Register @cfts to @ss.  Files described by @cfts are created for all
3845  * existing cgroups to which @ss is attached and all future cgroups will
3846  * have them too.  This function can be called anytime whether @ss is
3847  * attached or not.
3848  *
3849  * Returns 0 on successful registration, -errno on failure.  Note that this
3850  * function currently returns 0 as long as @cfts registration is successful
3851  * even if some file creation attempts on existing cgroups fail.
3852  */
3853 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3854 {
3855     int ret;
3856 
3857     if (!cgroup_ssid_enabled(ss->id))
3858         return 0;
3859 
3860     if (!cfts || cfts[0].name[0] == '\0')
3861         return 0;
3862 
3863     ret = cgroup_init_cftypes(ss, cfts);
3864     if (ret)
3865         return ret;
3866 
3867     mutex_lock(&cgroup_mutex);
3868 
3869     list_add_tail(&cfts->node, &ss->cfts);
3870     ret = cgroup_apply_cftypes(cfts, true);
3871     if (ret)
3872         cgroup_rm_cftypes_locked(cfts);
3873 
3874     mutex_unlock(&cgroup_mutex);
3875     return ret;
3876 }
3877 
3878 /**
3879  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3880  * @ss: target cgroup subsystem
3881  * @cfts: zero-length name terminated array of cftypes
3882  *
3883  * Similar to cgroup_add_cftypes() but the added files are only used for
3884  * the default hierarchy.
3885  */
3886 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3887 {
3888     struct cftype *cft;
3889 
3890     for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3891         cft->flags |= __CFTYPE_ONLY_ON_DFL;
3892     return cgroup_add_cftypes(ss, cfts);
3893 }
3894 
3895 /**
3896  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3897  * @ss: target cgroup subsystem
3898  * @cfts: zero-length name terminated array of cftypes
3899  *
3900  * Similar to cgroup_add_cftypes() but the added files are only used for
3901  * the legacy hierarchies.
3902  */
3903 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3904 {
3905     struct cftype *cft;
3906 
3907     for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3908         cft->flags |= __CFTYPE_NOT_ON_DFL;
3909     return cgroup_add_cftypes(ss, cfts);
3910 }
3911 
3912 /**
3913  * cgroup_file_notify - generate a file modified event for a cgroup_file
3914  * @cfile: target cgroup_file
3915  *
3916  * @cfile must have been obtained by setting cftype->file_offset.
3917  */
3918 void cgroup_file_notify(struct cgroup_file *cfile)
3919 {
3920     unsigned long flags;
3921 
3922     spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3923     if (cfile->kn)
3924         kernfs_notify(cfile->kn);
3925     spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3926 }
3927 
3928 /**
3929  * cgroup_task_count - count the number of tasks in a cgroup.
3930  * @cgrp: the cgroup in question
3931  *
3932  * Return the number of tasks in the cgroup.  The returned number can be
3933  * higher than the actual number of tasks due to css_set references from
3934  * namespace roots and temporary usages.
3935  */
3936 static int cgroup_task_count(const struct cgroup *cgrp)
3937 {
3938     int count = 0;
3939     struct cgrp_cset_link *link;
3940 
3941     spin_lock_irq(&css_set_lock);
3942     list_for_each_entry(link, &cgrp->cset_links, cset_link)
3943         count += atomic_read(&link->cset->refcount);
3944     spin_unlock_irq(&css_set_lock);
3945     return count;
3946 }
3947 
3948 /**
3949  * css_next_child - find the next child of a given css
3950  * @pos: the current position (%NULL to initiate traversal)
3951  * @parent: css whose children to walk
3952  *
3953  * This function returns the next child of @parent and should be called
3954  * under either cgroup_mutex or RCU read lock.  The only requirement is
3955  * that @parent and @pos are accessible.  The next sibling is guaranteed to
3956  * be returned regardless of their states.
3957  *
3958  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3959  * css which finished ->css_online() is guaranteed to be visible in the
3960  * future iterations and will stay visible until the last reference is put.
3961  * A css which hasn't finished ->css_online() or already finished
3962  * ->css_offline() may show up during traversal.  It's each subsystem's
3963  * responsibility to synchronize against on/offlining.
3964  */
3965 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3966                        struct cgroup_subsys_state *parent)
3967 {
3968     struct cgroup_subsys_state *next;
3969 
3970     cgroup_assert_mutex_or_rcu_locked();
3971 
3972     /*
3973      * @pos could already have been unlinked from the sibling list.
3974      * Once a cgroup is removed, its ->sibling.next is no longer
3975      * updated when its next sibling changes.  CSS_RELEASED is set when
3976      * @pos is taken off list, at which time its next pointer is valid,
3977      * and, as releases are serialized, the one pointed to by the next
3978      * pointer is guaranteed to not have started release yet.  This
3979      * implies that if we observe !CSS_RELEASED on @pos in this RCU
3980      * critical section, the one pointed to by its next pointer is
3981      * guaranteed to not have finished its RCU grace period even if we
3982      * have dropped rcu_read_lock() inbetween iterations.
3983      *
3984      * If @pos has CSS_RELEASED set, its next pointer can't be
3985      * dereferenced; however, as each css is given a monotonically
3986      * increasing unique serial number and always appended to the
3987      * sibling list, the next one can be found by walking the parent's
3988      * children until the first css with higher serial number than
3989      * @pos's.  While this path can be slower, it happens iff iteration
3990      * races against release and the race window is very small.
3991      */
3992     if (!pos) {
3993         next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3994     } else if (likely(!(pos->flags & CSS_RELEASED))) {
3995         next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3996     } else {
3997         list_for_each_entry_rcu(next, &parent->children, sibling)
3998             if (next->serial_nr > pos->serial_nr)
3999                 break;
4000     }
4001 
4002     /*
4003      * @next, if not pointing to the head, can be dereferenced and is
4004      * the next sibling.
4005      */
4006     if (&next->sibling != &parent->children)
4007         return next;
4008     return NULL;
4009 }
4010 
4011 /**
4012  * css_next_descendant_pre - find the next descendant for pre-order walk
4013  * @pos: the current position (%NULL to initiate traversal)
4014  * @root: css whose descendants to walk
4015  *
4016  * To be used by css_for_each_descendant_pre().  Find the next descendant
4017  * to visit for pre-order traversal of @root's descendants.  @root is
4018  * included in the iteration and the first node to be visited.
4019  *
4020  * While this function requires cgroup_mutex or RCU read locking, it
4021  * doesn't require the whole traversal to be contained in a single critical
4022  * section.  This function will return the correct next descendant as long
4023  * as both @pos and @root are accessible and @pos is a descendant of @root.
4024  *
4025  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4026  * css which finished ->css_online() is guaranteed to be visible in the
4027  * future iterations and will stay visible until the last reference is put.
4028  * A css which hasn't finished ->css_online() or already finished
4029  * ->css_offline() may show up during traversal.  It's each subsystem's
4030  * responsibility to synchronize against on/offlining.
4031  */
4032 struct cgroup_subsys_state *
4033 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4034             struct cgroup_subsys_state *root)
4035 {
4036     struct cgroup_subsys_state *next;
4037 
4038     cgroup_assert_mutex_or_rcu_locked();
4039 
4040     /* if first iteration, visit @root */
4041     if (!pos)
4042         return root;
4043 
4044     /* visit the first child if exists */
4045     next = css_next_child(NULL, pos);
4046     if (next)
4047         return next;
4048 
4049     /* no child, visit my or the closest ancestor's next sibling */
4050     while (pos != root) {
4051         next = css_next_child(pos, pos->parent);
4052         if (next)
4053             return next;
4054         pos = pos->parent;
4055     }
4056 
4057     return NULL;
4058 }
4059 
4060 /**
4061  * css_rightmost_descendant - return the rightmost descendant of a css
4062  * @pos: css of interest
4063  *
4064  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4065  * is returned.  This can be used during pre-order traversal to skip
4066  * subtree of @pos.
4067  *
4068  * While this function requires cgroup_mutex or RCU read locking, it
4069  * doesn't require the whole traversal to be contained in a single critical
4070  * section.  This function will return the correct rightmost descendant as
4071  * long as @pos is accessible.
4072  */
4073 struct cgroup_subsys_state *
4074 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4075 {
4076     struct cgroup_subsys_state *last, *tmp;
4077 
4078     cgroup_assert_mutex_or_rcu_locked();
4079 
4080     do {
4081         last = pos;
4082         /* ->prev isn't RCU safe, walk ->next till the end */
4083         pos = NULL;
4084         css_for_each_child(tmp, last)
4085             pos = tmp;
4086     } while (pos);
4087 
4088     return last;
4089 }
4090 
4091 static struct cgroup_subsys_state *
4092 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4093 {
4094     struct cgroup_subsys_state *last;
4095 
4096     do {
4097         last = pos;
4098         pos = css_next_child(NULL, pos);
4099     } while (pos);
4100 
4101     return last;
4102 }
4103 
4104 /**
4105  * css_next_descendant_post - find the next descendant for post-order walk
4106  * @pos: the current position (%NULL to initiate traversal)
4107  * @root: css whose descendants to walk
4108  *
4109  * To be used by css_for_each_descendant_post().  Find the next descendant
4110  * to visit for post-order traversal of @root's descendants.  @root is
4111  * included in the iteration and the last node to be visited.
4112  *
4113  * While this function requires cgroup_mutex or RCU read locking, it
4114  * doesn't require the whole traversal to be contained in a single critical
4115  * section.  This function will return the correct next descendant as long
4116  * as both @pos and @cgroup are accessible and @pos is a descendant of
4117  * @cgroup.
4118  *
4119  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4120  * css which finished ->css_online() is guaranteed to be visible in the
4121  * future iterations and will stay visible until the last reference is put.
4122  * A css which hasn't finished ->css_online() or already finished
4123  * ->css_offline() may show up during traversal.  It's each subsystem's
4124  * responsibility to synchronize against on/offlining.
4125  */
4126 struct cgroup_subsys_state *
4127 css_next_descendant_post(struct cgroup_subsys_state *pos,
4128              struct cgroup_subsys_state *root)
4129 {
4130     struct cgroup_subsys_state *next;
4131 
4132     cgroup_assert_mutex_or_rcu_locked();
4133 
4134     /* if first iteration, visit leftmost descendant which may be @root */
4135     if (!pos)
4136         return css_leftmost_descendant(root);
4137 
4138     /* if we visited @root, we're done */
4139     if (pos == root)
4140         return NULL;
4141 
4142     /* if there's an unvisited sibling, visit its leftmost descendant */
4143     next = css_next_child(pos, pos->parent);
4144     if (next)
4145         return css_leftmost_descendant(next);
4146 
4147     /* no sibling left, visit parent */
4148     return pos->parent;
4149 }
4150 
4151 /**
4152  * css_has_online_children - does a css have online children
4153  * @css: the target css
4154  *
4155  * Returns %true if @css has any online children; otherwise, %false.  This
4156  * function can be called from any context but the caller is responsible
4157  * for synchronizing against on/offlining as necessary.
4158  */
4159 bool css_has_online_children(struct cgroup_subsys_state *css)
4160 {
4161     struct cgroup_subsys_state *child;
4162     bool ret = false;
4163 
4164     rcu_read_lock();
4165     css_for_each_child(child, css) {
4166         if (child->flags & CSS_ONLINE) {
4167             ret = true;
4168             break;
4169         }
4170     }
4171     rcu_read_unlock();
4172     return ret;
4173 }
4174 
4175 /**
4176  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4177  * @it: the iterator to advance
4178  *
4179  * Advance @it to the next css_set to walk.
4180  */
4181 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4182 {
4183     struct list_head *l = it->cset_pos;
4184     struct cgrp_cset_link *link;
4185     struct css_set *cset;
4186 
4187     lockdep_assert_held(&css_set_lock);
4188 
4189     /* Advance to the next non-empty css_set */
4190     do {
4191         l = l->next;
4192         if (l == it->cset_head) {
4193             it->cset_pos = NULL;
4194             it->task_pos = NULL;
4195             return;
4196         }
4197 
4198         if (it->ss) {
4199             cset = container_of(l, struct css_set,
4200                         e_cset_node[it->ss->id]);
4201         } else {
4202             link = list_entry(l, struct cgrp_cset_link, cset_link);
4203             cset = link->cset;
4204         }
4205     } while (!css_set_populated(cset));
4206 
4207     it->cset_pos = l;
4208 
4209     if (!list_empty(&cset->tasks))
4210         it->task_pos = cset->tasks.next;
4211     else
4212         it->task_pos = cset->mg_tasks.next;
4213 
4214     it->tasks_head = &cset->tasks;
4215     it->mg_tasks_head = &cset->mg_tasks;
4216 
4217     /*
4218      * We don't keep css_sets locked across iteration steps and thus
4219      * need to take steps to ensure that iteration can be resumed after
4220      * the lock is re-acquired.  Iteration is performed at two levels -
4221      * css_sets and tasks in them.
4222      *
4223      * Once created, a css_set never leaves its cgroup lists, so a
4224      * pinned css_set is guaranteed to stay put and we can resume
4225      * iteration afterwards.
4226      *
4227      * Tasks may leave @cset across iteration steps.  This is resolved
4228      * by registering each iterator with the css_set currently being
4229      * walked and making css_set_move_task() advance iterators whose
4230      * next task is leaving.
4231      */
4232     if (it->cur_cset) {
4233         list_del(&it->iters_node);
4234         put_css_set_locked(it->cur_cset);
4235     }
4236     get_css_set(cset);
4237     it->cur_cset = cset;
4238     list_add(&it->iters_node, &cset->task_iters);
4239 }
4240 
4241 static void css_task_iter_advance(struct css_task_iter *it)
4242 {
4243     struct list_head *l = it->task_pos;
4244 
4245     lockdep_assert_held(&css_set_lock);
4246     WARN_ON_ONCE(!l);
4247 
4248     /*
4249      * Advance iterator to find next entry.  cset->tasks is consumed
4250      * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4251      * next cset.
4252      */
4253     l = l->next;
4254 
4255     if (l == it->tasks_head)
4256         l = it->mg_tasks_head->next;
4257 
4258     if (l == it->mg_tasks_head)
4259         css_task_iter_advance_css_set(it);
4260     else
4261         it->task_pos = l;
4262 }
4263 
4264 /**
4265  * css_task_iter_start - initiate task iteration
4266  * @css: the css to walk tasks of
4267  * @it: the task iterator to use
4268  *
4269  * Initiate iteration through the tasks of @css.  The caller can call
4270  * css_task_iter_next() to walk through the tasks until the function
4271  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4272  * called.
4273  */
4274 void css_task_iter_start(struct cgroup_subsys_state *css,
4275              struct css_task_iter *it)
4276 {
4277     /* no one should try to iterate before mounting cgroups */
4278     WARN_ON_ONCE(!use_task_css_set_links);
4279 
4280     memset(it, 0, sizeof(*it));
4281 
4282     spin_lock_irq(&css_set_lock);
4283 
4284     it->ss = css->ss;
4285 
4286     if (it->ss)
4287         it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4288     else
4289         it->cset_pos = &css->cgroup->cset_links;
4290 
4291     it->cset_head = it->cset_pos;
4292 
4293     css_task_iter_advance_css_set(it);
4294 
4295     spin_unlock_irq(&css_set_lock);
4296 }
4297 
4298 /**
4299  * css_task_iter_next - return the next task for the iterator
4300  * @it: the task iterator being iterated
4301  *
4302  * The "next" function for task iteration.  @it should have been
4303  * initialized via css_task_iter_start().  Returns NULL when the iteration
4304  * reaches the end.
4305  */
4306 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4307 {
4308     if (it->cur_task) {
4309         put_task_struct(it->cur_task);
4310         it->cur_task = NULL;
4311     }
4312 
4313     spin_lock_irq(&css_set_lock);
4314 
4315     if (it->task_pos) {
4316         it->cur_task = list_entry(it->task_pos, struct task_struct,
4317                       cg_list);
4318         get_task_struct(it->cur_task);
4319         css_task_iter_advance(it);
4320     }
4321 
4322     spin_unlock_irq(&css_set_lock);
4323 
4324     return it->cur_task;
4325 }
4326 
4327 /**
4328  * css_task_iter_end - finish task iteration
4329  * @it: the task iterator to finish
4330  *
4331  * Finish task iteration started by css_task_iter_start().
4332  */
4333 void css_task_iter_end(struct css_task_iter *it)
4334 {
4335     if (it->cur_cset) {
4336         spin_lock_irq(&css_set_lock);
4337         list_del(&it->iters_node);
4338         put_css_set_locked(it->cur_cset);
4339         spin_unlock_irq(&css_set_lock);
4340     }
4341 
4342     if (it->cur_task)
4343         put_task_struct(it->cur_task);
4344 }
4345 
4346 /**
4347  * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4348  * @to: cgroup to which the tasks will be moved
4349  * @from: cgroup in which the tasks currently reside
4350  *
4351  * Locking rules between cgroup_post_fork() and the migration path
4352  * guarantee that, if a task is forking while being migrated, the new child
4353  * is guaranteed to be either visible in the source cgroup after the
4354  * parent's migration is complete or put into the target cgroup.  No task
4355  * can slip out of migration through forking.
4356  */
4357 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
4358 {
4359     LIST_HEAD(preloaded_csets);
4360     struct cgrp_cset_link *link;
4361     struct css_task_iter it;
4362     struct task_struct *task;
4363     int ret;
4364 
4365     if (!cgroup_may_migrate_to(to))
4366         return -EBUSY;
4367 
4368     mutex_lock(&cgroup_mutex);
4369 
4370     percpu_down_write(&cgroup_threadgroup_rwsem);
4371 
4372     /* all tasks in @from are being moved, all csets are source */
4373     spin_lock_irq(&css_set_lock);
4374     list_for_each_entry(link, &from->cset_links, cset_link)
4375         cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4376     spin_unlock_irq(&css_set_lock);
4377 
4378     ret = cgroup_migrate_prepare_dst(&preloaded_csets);
4379     if (ret)
4380         goto out_err;
4381 
4382     /*
4383      * Migrate tasks one-by-one until @from is empty.  This fails iff
4384      * ->can_attach() fails.
4385      */
4386     do {
4387         css_task_iter_start(&from->self, &it);
4388         task = css_task_iter_next(&it);
4389         if (task)
4390             get_task_struct(task);
4391         css_task_iter_end(&it);
4392 
4393         if (task) {
4394             ret = cgroup_migrate(task, false, to->root);
4395             if (!ret)
4396                 trace_cgroup_transfer_tasks(to, task, false);
4397             put_task_struct(task);
4398         }
4399     } while (task && !ret);
4400 out_err:
4401     cgroup_migrate_finish(&preloaded_csets);
4402     percpu_up_write(&cgroup_threadgroup_rwsem);
4403     mutex_unlock(&cgroup_mutex);
4404     return ret;
4405 }
4406 
4407 /*
4408  * Stuff for reading the 'tasks'/'procs' files.
4409  *
4410  * Reading this file can return large amounts of data if a cgroup has
4411  * *lots* of attached tasks. So it may need several calls to read(),
4412  * but we cannot guarantee that the information we produce is correct
4413  * unless we produce it entirely atomically.
4414  *
4415  */
4416 
4417 /* which pidlist file are we talking about? */
4418 enum cgroup_filetype {
4419     CGROUP_FILE_PROCS,
4420     CGROUP_FILE_TASKS,
4421 };
4422 
4423 /*
4424  * A pidlist is a list of pids that virtually represents the contents of one
4425  * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4426  * a pair (one each for procs, tasks) for each pid namespace that's relevant
4427  * to the cgroup.
4428  */
4429 struct cgroup_pidlist {
4430     /*
4431      * used to find which pidlist is wanted. doesn't change as long as
4432      * this particular list stays in the list.
4433     */
4434     struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4435     /* array of xids */
4436     pid_t *list;
4437     /* how many elements the above list has */
4438     int length;
4439     /* each of these stored in a list by its cgroup */
4440     struct list_head links;
4441     /* pointer to the cgroup we belong to, for list removal purposes */
4442     struct cgroup *owner;
4443     /* for delayed destruction */
4444     struct delayed_work destroy_dwork;
4445 };
4446 
4447 /*
4448  * The following two functions "fix" the issue where there are more pids
4449  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4450  * TODO: replace with a kernel-wide solution to this problem
4451  */
4452 #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4453 static void *pidlist_allocate(int count)
4454 {
4455     if (PIDLIST_TOO_LARGE(count))
4456         return vmalloc(count * sizeof(pid_t));
4457     else
4458         return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4459 }
4460 
4461 static void pidlist_free(void *p)
4462 {
4463     kvfree(p);
4464 }
4465 
4466 /*
4467  * Used to destroy all pidlists lingering waiting for destroy timer.  None
4468  * should be left afterwards.
4469  */
4470 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4471 {
4472     struct cgroup_pidlist *l, *tmp_l;
4473 
4474     mutex_lock(&cgrp->pidlist_mutex);
4475     list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4476         mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4477     mutex_unlock(&cgrp->pidlist_mutex);
4478 
4479     flush_workqueue(cgroup_pidlist_destroy_wq);
4480     BUG_ON(!list_empty(&cgrp->pidlists));
4481 }
4482 
4483 static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4484 {
4485     struct delayed_work *dwork = to_delayed_work(work);
4486     struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4487                         destroy_dwork);
4488     struct cgroup_pidlist *tofree = NULL;
4489 
4490     mutex_lock(&l->owner->pidlist_mutex);
4491 
4492     /*
4493      * Destroy iff we didn't get queued again.  The state won't change
4494      * as destroy_dwork can only be queued while locked.
4495      */
4496     if (!delayed_work_pending(dwork)) {
4497         list_del(&l->links);
4498         pidlist_free(l->list);
4499         put_pid_ns(l->key.ns);
4500         tofree = l;
4501     }
4502 
4503     mutex_unlock(&l->owner->pidlist_mutex);
4504     kfree(tofree);
4505 }
4506 
4507 /*
4508  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4509  * Returns the number of unique elements.
4510  */
4511 static int pidlist_uniq(pid_t *list, int length)
4512 {
4513     int src, dest = 1;
4514 
4515     /*
4516      * we presume the 0th element is unique, so i starts at 1. trivial
4517      * edge cases first; no work needs to be done for either
4518      */
4519     if (length == 0 || length == 1)
4520         return length;
4521     /* src and dest walk down the list; dest counts unique elements */
4522     for (src = 1; src < length; src++) {
4523         /* find next unique element */
4524         while (list[src] == list[src-1]) {
4525             src++;
4526             if (src == length)
4527                 goto after;
4528         }
4529         /* dest always points to where the next unique element goes */
4530         list[dest] = list[src];
4531         dest++;
4532     }
4533 after:
4534     return dest;
4535 }
4536 
4537 /*
4538  * The two pid files - task and cgroup.procs - guaranteed that the result
4539  * is sorted, which forced this whole pidlist fiasco.  As pid order is
4540  * different per namespace, each namespace needs differently sorted list,
4541  * making it impossible to use, for example, single rbtree of member tasks
4542  * sorted by task pointer.  As pidlists can be fairly large, allocating one
4543  * per open file is dangerous, so cgroup had to implement shared pool of
4544  * pidlists keyed by cgroup and namespace.
4545  *
4546  * All this extra complexity was caused by the original implementation
4547  * committing to an entirely unnecessary property.  In the long term, we
4548  * want to do away with it.  Explicitly scramble sort order if on the
4549  * default hierarchy so that no such expectation exists in the new
4550  * interface.
4551  *
4552  * Scrambling is done by swapping every two consecutive bits, which is
4553  * non-identity one-to-one mapping which disturbs sort order sufficiently.
4554  */
4555 static pid_t pid_fry(pid_t pid)
4556 {
4557     unsigned a = pid & 0x55555555;
4558     unsigned b = pid & 0xAAAAAAAA;
4559 
4560     return (a << 1) | (b >> 1);
4561 }
4562 
4563 static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4564 {
4565     if (cgroup_on_dfl(cgrp))
4566         return pid_fry(pid);
4567     else
4568         return pid;
4569 }
4570 
4571 static int cmppid(const void *a, const void *b)
4572 {
4573     return *(pid_t *)a - *(pid_t *)b;
4574 }
4575 
4576 static int fried_cmppid(const void *a, const void *b)
4577 {
4578     return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
4579 }
4580 
4581 static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
4582                           enum cgroup_filetype type)
4583 {
4584     struct cgroup_pidlist *l;
4585     /* don't need task_nsproxy() if we're looking at ourself */
4586     struct pid_namespace *ns = task_active_pid_ns(current);
4587 
4588     lockdep_assert_held(&cgrp->pidlist_mutex);
4589 
4590     list_for_each_entry(l, &cgrp->pidlists, links)
4591         if (l->key.type == type && l->key.ns == ns)
4592             return l;
4593     return NULL;
4594 }
4595 
4596 /*
4597  * find the appropriate pidlist for our purpose (given procs vs tasks)
4598  * returns with the lock on that pidlist already held, and takes care
4599  * of the use count, or returns NULL with no locks held if we're out of
4600  * memory.
4601  */
4602 static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
4603                         enum cgroup_filetype type)
4604 {
4605     struct cgroup_pidlist *l;
4606 
4607     lockdep_assert_held(&cgrp->pidlist_mutex);
4608 
4609     l = cgroup_pidlist_find(cgrp, type);
4610     if (l)
4611         return l;
4612 
4613     /* entry not found; create a new one */
4614     l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4615     if (!l)
4616         return l;
4617 
4618     INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4619     l->key.type = type;
4620     /* don't need task_nsproxy() if we're looking at ourself */
4621     l->key.ns = get_pid_ns(task_active_pid_ns(current));
4622     l->owner = cgrp;
4623     list_add(&l->links, &cgrp->pidlists);
4624     return l;
4625 }
4626 
4627 /*
4628  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
4629  */
4630 static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4631                   struct cgroup_pidlist **lp)
4632 {
4633     pid_t *array;
4634     int length;
4635     int pid, n = 0; /* used for populating the array */
4636     struct css_task_iter it;
4637     struct task_struct *tsk;
4638     struct cgroup_pidlist *l;
4639 
4640     lockdep_assert_held(&cgrp->pidlist_mutex);
4641 
4642     /*
4643      * If cgroup gets more users after we read count, we won't have
4644      * enough space - tough.  This race is indistinguishable to the
4645      * caller from the case that the additional cgroup users didn't
4646      * show up until sometime later on.
4647      */
4648     length = cgroup_task_count(cgrp);
4649     array = pidlist_allocate(length);
4650     if (!array)
4651         return -ENOMEM;
4652     /* now, populate the array */
4653     css_task_iter_start(&cgrp->self, &it);
4654     while ((tsk = css_task_iter_next(&it))) {
4655         if (unlikely(n == length))
4656             break;
4657         /* get tgid or pid for procs or tasks file respectively */
4658         if (type == CGROUP_FILE_PROCS)
4659             pid = task_tgid_vnr(tsk);
4660         else
4661             pid = task_pid_vnr(tsk);
4662         if (pid > 0) /* make sure to only use valid results */
4663             array[n++] = pid;
4664     }
4665     css_task_iter_end(&it);
4666     length = n;
4667     /* now sort & (if procs) strip out duplicates */
4668     if (cgroup_on_dfl(cgrp))
4669         sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4670     else
4671         sort(array, length, sizeof(pid_t), cmppid, NULL);
4672     if (type == CGROUP_FILE_PROCS)
4673         length = pidlist_uniq(array, length);
4674 
4675     l = cgroup_pidlist_find_create(cgrp, type);
4676     if (!l) {
4677         pidlist_free(array);
4678         return -ENOMEM;
4679     }
4680 
4681     /* store array, freeing old if necessary */
4682     pidlist_free(l->list);
4683     l->list = array;
4684     l->length = length;
4685     *lp = l;
4686     return 0;
4687 }
4688 
4689 /**
4690  * cgroupstats_build - build and fill cgroupstats
4691  * @stats: cgroupstats to fill information into
4692  * @dentry: A dentry entry belonging to the cgroup for which stats have
4693  * been requested.
4694  *
4695  * Build and fill cgroupstats so that taskstats can export it to user
4696  * space.
4697  */
4698 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
4699 {
4700     struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4701     struct cgroup *cgrp;
4702     struct css_task_iter it;
4703     struct task_struct *tsk;
4704 
4705     /* it should be kernfs_node belonging to cgroupfs and is a directory */
4706     if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4707         kernfs_type(kn) != KERNFS_DIR)
4708         return -EINVAL;
4709 
4710     mutex_lock(&cgroup_mutex);
4711 
4712     /*
4713      * We aren't being called from kernfs and there's no guarantee on
4714      * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
4715      * @kn->priv is RCU safe.  Let's do the RCU dancing.
4716      */
4717     rcu_read_lock();
4718     cgrp = rcu_dereference(kn->priv);
4719     if (!cgrp || cgroup_is_dead(cgrp)) {
4720         rcu_read_unlock();
4721         mutex_unlock(&cgroup_mutex);
4722         return -ENOENT;
4723     }
4724     rcu_read_unlock();
4725 
4726     css_task_iter_start(&cgrp->self, &it);
4727     while ((tsk = css_task_iter_next(&it))) {
4728         switch (tsk->state) {
4729         case TASK_RUNNING:
4730             stats->nr_running++;
4731             break;
4732         case TASK_INTERRUPTIBLE:
4733             stats->nr_sleeping++;
4734             break;
4735         case TASK_UNINTERRUPTIBLE:
4736             stats->nr_uninterruptible++;
4737             break;
4738         case TASK_STOPPED:
4739             stats->nr_stopped++;
4740             break;
4741         default:
4742             if (delayacct_is_task_waiting_on_io(tsk))
4743                 stats->nr_io_wait++;
4744             break;
4745         }
4746     }
4747     css_task_iter_end(&it);
4748 
4749     mutex_unlock(&cgroup_mutex);
4750     return 0;
4751 }
4752 
4753 
4754 /*
4755  * seq_file methods for the tasks/procs files. The seq_file position is the
4756  * next pid to display; the seq_file iterator is a pointer to the pid
4757  * in the cgroup->l->list array.
4758  */
4759 
4760 static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
4761 {
4762     /*
4763      * Initially we receive a position value that corresponds to
4764      * one more than the last pid shown (or 0 on the first call or
4765      * after a seek to the start). Use a binary-search to find the
4766      * next pid to display, if any
4767      */
4768     struct kernfs_open_file *of = s->private;
4769     struct cgroup *cgrp = seq_css(s)->cgroup;
4770     struct cgroup_pidlist *l;
4771     enum cgroup_filetype type = seq_cft(s)->private;
4772     int index = 0, pid = *pos;
4773     int *iter, ret;
4774 
4775     mutex_lock(&cgrp->pidlist_mutex);
4776 
4777     /*
4778      * !NULL @of->priv indicates that this isn't the first start()
4779      * after open.  If the matching pidlist is around, we can use that.
4780      * Look for it.  Note that @of->priv can't be used directly.  It
4781      * could already have been destroyed.
4782      */
4783     if (of->priv)
4784         of->priv = cgroup_pidlist_find(cgrp, type);
4785 
4786     /*
4787      * Either this is the first start() after open or the matching
4788      * pidlist has been destroyed inbetween.  Create a new one.
4789      */
4790     if (!of->priv) {
4791         ret = pidlist_array_load(cgrp, type,
4792                      (struct cgroup_pidlist **)&of->priv);
4793         if (ret)
4794             return ERR_PTR(ret);
4795     }
4796     l = of->priv;
4797 
4798     if (pid) {
4799         int end = l->length;
4800 
4801         while (index < end) {
4802             int mid = (index + end) / 2;
4803             if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4804                 index = mid;
4805                 break;
4806             } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4807                 index = mid + 1;
4808             else
4809                 end = mid;
4810         }
4811     }
4812     /* If we're off the end of the array, we're done */
4813     if (index >= l->length)
4814         return NULL;
4815     /* Update the abstract position to be the actual pid that we found */
4816     iter = l->list + index;
4817     *pos = cgroup_pid_fry(cgrp, *iter);
4818     return iter;
4819 }
4820 
4821 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
4822 {
4823     struct kernfs_open_file *of = s->private;
4824     struct cgroup_pidlist *l = of->priv;
4825 
4826     if (l)
4827         mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4828                  CGROUP_PIDLIST_DESTROY_DELAY);
4829     mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4830 }
4831 
4832 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
4833 {
4834     struct kernfs_open_file *of = s->private;
4835     struct cgroup_pidlist *l = of->priv;
4836     pid_t *p = v;
4837     pid_t *end = l->list + l->length;
4838     /*
4839      * Advance to the next pid in the array. If this goes off the
4840      * end, we're done
4841      */
4842     p++;
4843     if (p >= end) {
4844         return NULL;
4845     } else {
4846         *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
4847         return p;
4848     }
4849 }
4850 
4851 static int cgroup_pidlist_show(struct seq_file *s, void *v)
4852 {
4853     seq_printf(s, "%d\n", *(int *)v);
4854 
4855     return 0;
4856 }
4857 
4858 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4859                      struct cftype *cft)
4860 {
4861     return notify_on_release(css->cgroup);
4862 }
4863 
4864 static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4865                       struct cftype *cft, u64 val)
4866 {
4867     if (val)
4868         set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4869     else
4870         clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4871     return 0;
4872 }
4873 
4874 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4875                       struct cftype *cft)
4876 {
4877     return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4878 }
4879 
4880 static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4881                        struct cftype *cft, u64 val)
4882 {
4883     if (val)
4884         set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4885     else
4886         clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4887     return 0;
4888 }
4889 
4890 /* cgroup core interface files for the default hierarchy */
4891 static struct cftype cgroup_dfl_base_files[] = {
4892     {
4893         .name = "cgroup.procs",
4894         .file_offset = offsetof(struct cgroup, procs_file),
4895         .seq_start = cgroup_pidlist_start,
4896         .seq_next = cgroup_pidlist_next,
4897         .seq_stop = cgroup_pidlist_stop,
4898         .seq_show = cgroup_pidlist_show,
4899         .private = CGROUP_FILE_PROCS,
4900         .write = cgroup_procs_write,
4901     },
4902     {
4903         .name = "cgroup.controllers",
4904         .seq_show = cgroup_controllers_show,
4905     },
4906     {
4907         .name = "cgroup.subtree_control",
4908         .seq_show = cgroup_subtree_control_show,
4909         .write = cgroup_subtree_control_write,
4910     },
4911     {
4912         .name = "cgroup.events",
4913         .flags = CFTYPE_NOT_ON_ROOT,
4914         .file_offset = offsetof(struct cgroup, events_file),
4915         .seq_show = cgroup_events_show,
4916     },
4917     { } /* terminate */
4918 };
4919 
4920 /* cgroup core interface files for the legacy hierarchies */
4921 static struct cftype cgroup_legacy_base_files[] = {
4922     {
4923         .name = "cgroup.procs",
4924         .seq_start = cgroup_pidlist_start,
4925         .seq_next = cgroup_pidlist_next,
4926         .seq_stop = cgroup_pidlist_stop,
4927         .seq_show = cgroup_pidlist_show,
4928         .private = CGROUP_FILE_PROCS,
4929         .write = cgroup_procs_write,
4930     },
4931     {
4932         .name = "cgroup.clone_children",
4933         .read_u64 = cgroup_clone_children_read,
4934         .write_u64 = cgroup_clone_children_write,
4935     },
4936     {
4937         .name = "cgroup.sane_behavior",
4938         .flags = CFTYPE_ONLY_ON_ROOT,
4939         .seq_show = cgroup_sane_behavior_show,
4940     },
4941     {
4942         .name = "tasks",
4943         .seq_start = cgroup_pidlist_start,
4944         .seq_next = cgroup_pidlist_next,
4945         .seq_stop = cgroup_pidlist_stop,
4946         .seq_show = cgroup_pidlist_show,
4947         .private = CGROUP_FILE_TASKS,
4948         .write = cgroup_tasks_write,
4949     },
4950     {
4951         .name = "notify_on_release",
4952         .read_u64 = cgroup_read_notify_on_release,
4953         .write_u64 = cgroup_write_notify_on_release,
4954     },
4955     {
4956         .name = "release_agent",
4957         .flags = CFTYPE_ONLY_ON_ROOT,
4958         .seq_show = cgroup_release_agent_show,
4959         .write = cgroup_release_agent_write,
4960         .max_write_len = PATH_MAX - 1,
4961     },
4962     { } /* terminate */
4963 };
4964 
4965 /*
4966  * css destruction is four-stage process.
4967  *
4968  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4969  *    Implemented in kill_css().
4970  *
4971  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4972  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4973  *    offlined by invoking offline_css().  After offlining, the base ref is
4974  *    put.  Implemented in css_killed_work_fn().
4975  *
4976  * 3. When the percpu_ref reaches zero, the only possible remaining
4977  *    accessors are inside RCU read sections.  css_release() schedules the
4978  *    RCU callback.
4979  *
4980  * 4. After the grace period, the css can be freed.  Implemented in
4981  *    css_free_work_fn().
4982  *
4983  * It is actually hairier because both step 2 and 4 require process context
4984  * and thus involve punting to css->destroy_work adding two additional
4985  * steps to the already complex sequence.
4986  */
4987 static void css_free_work_fn(struct work_struct *work)
4988 {
4989     struct cgroup_subsys_state *css =
4990         container_of(work, struct cgroup_subsys_state, destroy_work);
4991     struct cgroup_subsys *ss = css->ss;
4992     struct cgroup *cgrp = css->cgroup;
4993 
4994     percpu_ref_exit(&css->refcnt);
4995 
4996     if (ss) {
4997         /* css free path */
4998         struct cgroup_subsys_state *parent = css->parent;
4999         int id = css->id;
5000 
5001         ss->css_free(css);
5002         cgroup_idr_remove(&ss->css_idr, id);
5003         cgroup_put(cgrp);
5004 
5005         if (parent)
5006             css_put(parent);
5007     } else {
5008         /* cgroup free path */
5009         atomic_dec(&cgrp->root->nr_cgrps);
5010         cgroup_pidlist_destroy_all(cgrp);
5011         cancel_work_sync(&cgrp->release_agent_work);
5012 
5013         if (cgroup_parent(cgrp)) {
5014             /*
5015              * We get a ref to the parent, and put the ref when
5016              * this cgroup is being freed, so it's guaranteed
5017              * that the parent won't be destroyed before its
5018              * children.
5019              */
5020             cgroup_put(cgroup_parent(cgrp));
5021             kernfs_put(cgrp->kn);
5022             kfree(cgrp);
5023         } else {
5024             /*
5025              * This is root cgroup's refcnt reaching zero,
5026              * which indicates that the root should be
5027              * released.
5028              */
5029             cgroup_destroy_root(cgrp->root);
5030         }
5031     }
5032 }
5033 
5034 static void css_free_rcu_fn(struct rcu_head *rcu_head)
5035 {
5036     struct cgroup_subsys_state *css =
5037         container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
5038 
5039     INIT_WORK(&css->destroy_work, css_free_work_fn);
5040     queue_work(cgroup_destroy_wq, &css->destroy_work);
5041 }
5042 
5043 static void css_release_work_fn(struct work_struct *work)
5044 {
5045     struct cgroup_subsys_state *css =
5046         container_of(work, struct cgroup_subsys_state, destroy_work);
5047     struct cgroup_subsys *ss = css->ss;
5048     struct cgroup *cgrp = css->cgroup;
5049 
5050     mutex_lock(&cgroup_mutex);
5051 
5052     css->flags |= CSS_RELEASED;
5053     list_del_rcu(&css->sibling);
5054 
5055     if (ss) {
5056         /* css release path */
5057         cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5058         if (ss->css_released)
5059             ss->css_released(css);
5060     } else {
5061         /* cgroup release path */
5062         trace_cgroup_release(cgrp);
5063 
5064         cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5065         cgrp->id = -1;
5066 
5067         /*
5068          * There are two control paths which try to determine
5069          * cgroup from dentry without going through kernfs -
5070          * cgroupstats_build() and css_tryget_online_from_dir().
5071          * Those are supported by RCU protecting clearing of
5072          * cgrp->kn->priv backpointer.
5073          */
5074         if (cgrp->kn)
5075             RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5076                      NULL);
5077 
5078         cgroup_bpf_put(cgrp);
5079     }
5080 
5081     mutex_unlock(&cgroup_mutex);
5082 
5083     call_rcu(&css->rcu_head, css_free_rcu_fn);
5084 }
5085 
5086 static void css_release(struct percpu_ref *ref)
5087 {
5088     struct cgroup_subsys_state *css =
5089         container_of(ref, struct cgroup_subsys_state, refcnt);
5090 
5091     INIT_WORK(&css->destroy_work, css_release_work_fn);
5092     queue_work(cgroup_destroy_wq, &css->destroy_work);
5093 }
5094 
5095 static void init_and_link_css(struct cgroup_subsys_state *css,
5096                   struct cgroup_subsys *ss, struct cgroup *cgrp)
5097 {
5098     lockdep_assert_held(&cgroup_mutex);
5099 
5100     cgroup_get(cgrp);
5101 
5102     memset(css, 0, sizeof(*css));
5103     css->cgroup = cgrp;
5104     css->ss = ss;
5105     css->id = -1;
5106     INIT_LIST_HEAD(&css->sibling);
5107     INIT_LIST_HEAD(&css->children);
5108     css->serial_nr = css_serial_nr_next++;
5109     atomic_set(&css->online_cnt, 0);
5110 
5111     if (cgroup_parent(cgrp)) {
5112         css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5113         css_get(css->parent);
5114     }
5115 
5116     BUG_ON(cgroup_css(cgrp, ss));
5117 }
5118 
5119 /* invoke ->css_online() on a new CSS and mark it online if successful */
5120 static int online_css(struct cgroup_subsys_state *css)
5121 {
5122     struct cgroup_subsys *ss = css->ss;
5123     int ret = 0;
5124 
5125     lockdep_assert_held(&cgroup_mutex);
5126 
5127     if (ss->css_online)
5128         ret = ss->css_online(css);
5129     if (!ret) {
5130         css->flags |= CSS_ONLINE;
5131         rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5132 
5133         atomic_inc(&css->online_cnt);
5134         if (css->parent)
5135             atomic_inc(&css->parent->online_cnt);
5136     }
5137     return ret;
5138 }
5139 
5140 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5141 static void offline_css(struct cgroup_subsys_state *css)
5142 {
5143     struct cgroup_subsys *ss = css->ss;
5144 
5145     lockdep_assert_held(&cgroup_mutex);
5146 
5147     if (!(css->flags & CSS_ONLINE))
5148         return;
5149 
5150     if (ss->css_reset)
5151         ss->css_reset(css);
5152 
5153     if (ss->css_offline)
5154         ss->css_offline(css);
5155 
5156     css->flags &= ~CSS_ONLINE;
5157     RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5158 
5159     wake_up_all(&css->cgroup->offline_waitq);
5160 }
5161 
5162 /**
5163  * css_create - create a cgroup_subsys_state
5164  * @cgrp: the cgroup new css will be associated with
5165  * @ss: the subsys of new css
5166  *
5167  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5168  * css is online and installed in @cgrp.  This function doesn't create the
5169  * interface files.  Returns 0 on success, -errno on failure.
5170  */
5171 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5172                           struct cgroup_subsys *ss)
5173 {
5174     struct cgroup *parent = cgroup_parent(cgrp);
5175     struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5176     struct cgroup_subsys_state *css;
5177     int err;
5178 
5179     lockdep_assert_held(&cgroup_mutex);
5180 
5181     css = ss->css_alloc(parent_css);
5182     if (!css)
5183         css = ERR_PTR(-ENOMEM);
5184     if (IS_ERR(css))
5185         return css;
5186 
5187     init_and_link_css(css, ss, cgrp);
5188 
5189     err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5190     if (err)
5191         goto err_free_css;
5192 
5193     err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5194     if (err < 0)
5195         goto err_free_css;
5196     css->id = err;
5197 
5198     /* @css is ready to be brought online now, make it visible */
5199     list_add_tail_rcu(&css->sibling, &parent_css->children);
5200     cgroup_idr_replace(&ss->css_idr, css, css->id);
5201 
5202     err = online_css(css);
5203     if (err)
5204         goto err_list_del;
5205 
5206     if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5207         cgroup_parent(parent)) {
5208         pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5209             current->comm, current->pid, ss->name);
5210         if (!strcmp(ss->name, "memory"))
5211             pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5212         ss->warned_broken_hierarchy = true;
5213     }
5214 
5215     return css;
5216 
5217 err_list_del:
5218     list_del_rcu(&css->sibling);
5219 err_free_css:
5220     call_rcu(&css->rcu_head, css_free_rcu_fn);
5221     return ERR_PTR(err);
5222 }
5223 
5224 /*
5225  * The returned cgroup is fully initialized including its control mask, but
5226  * it isn't associated with its kernfs_node and doesn't have the control
5227  * mask applied.
5228  */
5229 static struct cgroup *cgroup_create(struct cgroup *parent)
5230 {
5231     struct cgroup_root *root = parent->root;
5232     struct cgroup *cgrp, *tcgrp;
5233     int level = parent->level + 1;
5234     int ret;
5235 
5236     /* allocate the cgroup and its ID, 0 is reserved for the root */
5237     cgrp = kzalloc(sizeof(*cgrp) +
5238                sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
5239     if (!cgrp)
5240         return ERR_PTR(-ENOMEM);
5241 
5242     ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5243     if (ret)
5244         goto out_free_cgrp;
5245 
5246     /*
5247      * Temporarily set the pointer to NULL, so idr_find() won't return
5248      * a half-baked cgroup.
5249      */
5250     cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5251     if (cgrp->id < 0) {
5252         ret = -ENOMEM;
5253         goto out_cancel_ref;
5254     }
5255 
5256     init_cgroup_housekeeping(cgrp);
5257 
5258     cgrp->self.parent = &parent->self;
5259     cgrp->root = root;
5260     cgrp->level = level;
5261 
5262     for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
5263         cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5264 
5265     if (notify_on_release(parent))
5266         set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5267 
5268     if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5269         set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5270 
5271     cgrp->self.serial_nr = css_serial_nr_next++;
5272 
5273     /* allocation complete, commit to creation */
5274     list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5275     atomic_inc(&root->nr_cgrps);
5276     cgroup_get(parent);
5277 
5278     /*
5279      * @cgrp is now fully operational.  If something fails after this
5280      * point, it'll be released via the normal destruction path.
5281      */
5282     cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5283 
5284     /*
5285      * On the default hierarchy, a child doesn't automatically inherit
5286      * subtree_control from the parent.  Each is configured manually.
5287      */
5288     if (!cgroup_on_dfl(cgrp))
5289         cgrp->subtree_control = cgroup_control(cgrp);
5290 
5291     if (parent)
5292         cgroup_bpf_inherit(cgrp, parent);
5293 
5294     cgroup_propagate_control(cgrp);
5295 
5296     return cgrp;
5297 
5298 out_cancel_ref:
5299     percpu_ref_exit(&cgrp->self.refcnt);
5300 out_free_cgrp:
5301     kfree(cgrp);
5302     return ERR_PTR(ret);
5303 }
5304 
5305 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
5306             umode_t mode)
5307 {
5308     struct cgroup *parent, *cgrp;
5309     struct kernfs_node *kn;
5310     int ret;
5311 
5312     /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5313     if (strchr(name, '\n'))
5314         return -EINVAL;
5315 
5316     parent = cgroup_kn_lock_live(parent_kn, false);
5317     if (!parent)
5318         return -ENODEV;
5319 
5320     cgrp = cgroup_create(parent);
5321     if (IS_ERR(cgrp)) {
5322         ret = PTR_ERR(cgrp);
5323         goto out_unlock;
5324     }
5325 
5326     /* create the directory */
5327     kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5328     if (IS_ERR(kn)) {
5329         ret = PTR_ERR(kn);
5330         goto out_destroy;
5331     }
5332     cgrp->kn = kn;
5333 
5334     /*
5335      * This extra ref will be put in cgroup_free_fn() and guarantees
5336      * that @cgrp->kn is always accessible.
5337      */
5338     kernfs_get(kn);
5339 
5340     ret = cgroup_kn_set_ugid(kn);
5341     if (ret)
5342         goto out_destroy;
5343 
5344     ret = css_populate_dir(&cgrp->self);
5345     if (ret)
5346         goto out_destroy;
5347 
5348     ret = cgroup_apply_control_enable(cgrp);
5349     if (ret)
5350         goto out_destroy;
5351 
5352     trace_cgroup_mkdir(cgrp);
5353 
5354     /* let's create and online css's */
5355     kernfs_activate(kn);
5356 
5357     ret = 0;
5358     goto out_unlock;
5359 
5360 out_destroy:
5361     cgroup_destroy_locked(cgrp);
5362 out_unlock:
5363     cgroup_kn_unlock(parent_kn);
5364     return ret;
5365 }
5366 
5367 /*
5368  * This is called when the refcnt of a css is confirmed to be killed.
5369  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5370  * initate destruction and put the css ref from kill_css().
5371  */
5372 static void css_killed_work_fn(struct work_struct *work)
5373 {
5374     struct cgroup_subsys_state *css =
5375         container_of(work, struct cgroup_subsys_state, destroy_work);
5376 
5377     mutex_lock(&cgroup_mutex);
5378 
5379     do {
5380         offline_css(css);
5381         css_put(css);
5382         /* @css can't go away while we're holding cgroup_mutex */
5383         css = css->parent;
5384     } while (css && atomic_dec_and_test(&css->online_cnt));
5385 
5386     mutex_unlock(&cgroup_mutex);
5387 }
5388 
5389 /* css kill confirmation processing requires process context, bounce */
5390 static void css_killed_ref_fn(struct percpu_ref *ref)
5391 {
5392     struct cgroup_subsys_state *css =
5393         container_of(ref, struct cgroup_subsys_state, refcnt);
5394 
5395     if (atomic_dec_and_test(&css->online_cnt)) {
5396         INIT_WORK(&css->destroy_work, css_killed_work_fn);
5397         queue_work(cgroup_destroy_wq, &css->destroy_work);
5398     }
5399 }
5400 
5401 /**
5402  * kill_css - destroy a css
5403  * @css: css to destroy
5404  *
5405  * This function initiates destruction of @css by removing cgroup interface
5406  * files and putting its base reference.  ->css_offline() will be invoked
5407  * asynchronously once css_tryget_online() is guaranteed to fail and when
5408  * the reference count reaches zero, @css will be released.
5409  */
5410 static void kill_css(struct cgroup_subsys_state *css)
5411 {
5412     lockdep_assert_held(&cgroup_mutex);
5413 
5414     /*
5415      * This must happen before css is disassociated with its cgroup.
5416      * See seq_css() for details.
5417      */
5418     css_clear_dir(css);
5419 
5420     /*
5421      * Killing would put the base ref, but we need to keep it alive
5422      * until after ->css_offline().
5423      */
5424     css_get(css);
5425 
5426     /*
5427      * cgroup core guarantees that, by the time ->css_offline() is
5428      * invoked, no new css reference will be given out via
5429      * css_tryget_online().  We can't simply call percpu_ref_kill() and
5430      * proceed to offlining css's because percpu_ref_kill() doesn't
5431      * guarantee that the ref is seen as killed on all CPUs on return.
5432      *
5433      * Use percpu_ref_kill_and_confirm() to get notifications as each
5434      * css is confirmed to be seen as killed on all CPUs.
5435      */
5436     percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5437 }
5438 
5439 /**
5440  * cgroup_destroy_locked - the first stage of cgroup destruction
5441  * @cgrp: cgroup to be destroyed
5442  *
5443  * css's make use of percpu refcnts whose killing latency shouldn't be
5444  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5445  * guarantee that css_tryget_online() won't succeed by the time
5446  * ->css_offline() is invoked.  To satisfy all the requirements,
5447  * destruction is implemented in the following two steps.
5448  *
5449  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5450  *     userland visible parts and start killing the percpu refcnts of
5451  *     css's.  Set up so that the next stage will be kicked off once all
5452  *     the percpu refcnts are confirmed to be killed.
5453  *
5454  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5455  *     rest of destruction.  Once all cgroup references are gone, the
5456  *     cgroup is RCU-freed.
5457  *
5458  * This function implements s1.  After this step, @cgrp is gone as far as
5459  * the userland is concerned and a new cgroup with the same name may be
5460  * created.  As cgroup doesn't care about the names internally, this
5461  * doesn't cause any problem.
5462  */
5463 static int cgroup_destroy_locked(struct cgroup *cgrp)
5464     __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5465 {
5466     struct cgroup_subsys_state *css;
5467     struct cgrp_cset_link *link;
5468     int ssid;
5469 
5470     lockdep_assert_held(&cgroup_mutex);
5471 
5472     /*
5473      * Only migration can raise populated from zero and we're already
5474      * holding cgroup_mutex.
5475      */
5476     if (cgroup_is_populated(cgrp))
5477         return -EBUSY;
5478 
5479     /*
5480      * Make sure there's no live children.  We can't test emptiness of
5481      * ->self.children as dead children linger on it while being
5482      * drained; otherwise, "rmdir parent/child parent" may fail.
5483      */
5484     if (css_has_online_children(&cgrp->self))
5485         return -EBUSY;
5486 
5487     /*
5488      * Mark @cgrp and the associated csets dead.  The former prevents
5489      * further task migration and child creation by disabling
5490      * cgroup_lock_live_group().  The latter makes the csets ignored by
5491      * the migration path.
5492      */
5493     cgrp->self.flags &= ~CSS_ONLINE;
5494 
5495     spin_lock_irq(&css_set_lock);
5496     list_for_each_entry(link, &cgrp->cset_links, cset_link)
5497         link->cset->dead = true;
5498     spin_unlock_irq(&css_set_lock);
5499 
5500     /* initiate massacre of all css's */
5501     for_each_css(css, ssid, cgrp)
5502         kill_css(css);
5503 
5504     /*
5505      * Remove @cgrp directory along with the base files.  @cgrp has an
5506      * extra ref on its kn.
5507      */
5508     kernfs_remove(cgrp->kn);
5509 
5510     check_for_release(cgroup_parent(cgrp));
5511 
5512     /* put the base reference */
5513     percpu_ref_kill(&cgrp->self.refcnt);
5514 
5515     return 0;
5516 };
5517 
5518 static int cgroup_rmdir(struct kernfs_node *kn)
5519 {
5520     struct cgroup *cgrp;
5521     int ret = 0;
5522 
5523     cgrp = cgroup_kn_lock_live(kn, false);
5524     if (!cgrp)
5525         return 0;
5526 
5527     ret = cgroup_destroy_locked(cgrp);
5528 
5529     if (!ret)
5530         trace_cgroup_rmdir(cgrp);
5531 
5532     cgroup_kn_unlock(kn);
5533     return ret;
5534 }
5535 
5536 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5537     .remount_fs     = cgroup_remount,
5538     .show_options       = cgroup_show_options,
5539     .mkdir          = cgroup_mkdir,
5540     .rmdir          = cgroup_rmdir,
5541     .rename         = cgroup_rename,
5542     .show_path      = cgroup_show_path,
5543 };
5544 
5545 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5546 {
5547     struct cgroup_subsys_state *css;
5548 
5549     pr_debug("Initializing cgroup subsys %s\n", ss->name);
5550 
5551     mutex_lock(&cgroup_mutex);
5552 
5553     idr_init(&ss->css_idr);
5554     INIT_LIST_HEAD(&ss->cfts);
5555 
5556     /* Create the root cgroup state for this subsystem */
5557     ss->root = &cgrp_dfl_root;
5558     css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5559     /* We don't handle early failures gracefully */
5560     BUG_ON(IS_ERR(css));
5561     init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5562 
5563     /*
5564      * Root csses are never destroyed and we can't initialize
5565      * percpu_ref during early init.  Disable refcnting.
5566      */
5567     css->flags |= CSS_NO_REF;
5568 
5569     if (early) {
5570         /* allocation can't be done safely during early init */
5571         css->id = 1;
5572     } else {
5573         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5574         BUG_ON(css->id < 0);
5575     }
5576 
5577     /* Update the init_css_set to contain a subsys
5578      * pointer to this state - since the subsystem is
5579      * newly registered, all tasks and hence the
5580      * init_css_set is in the subsystem's root cgroup. */
5581     init_css_set.subsys[ss->id] = css;
5582 
5583     have_fork_callback |= (bool)ss->fork << ss->id;
5584     have_exit_callback |= (bool)ss->exit << ss->id;
5585     have_free_callback |= (bool)ss->free << ss->id;
5586     have_canfork_callback |= (bool)ss->can_fork << ss->id;
5587 
5588     /* At system boot, before all subsystems have been
5589      * registered, no tasks have been forked, so we don't
5590      * need to invoke fork callbacks here. */
5591     BUG_ON(!list_empty(&init_task.tasks));
5592 
5593     BUG_ON(online_css(css));
5594 
5595     mutex_unlock(&cgroup_mutex);
5596 }
5597 
5598 /**
5599  * cgroup_init_early - cgroup initialization at system boot
5600  *
5601  * Initialize cgroups at system boot, and initialize any
5602  * subsystems that request early init.
5603  */
5604 int __init cgroup_init_early(void)
5605 {
5606     static struct cgroup_sb_opts __initdata opts;
5607     struct cgroup_subsys *ss;
5608     int i;
5609 
5610     init_cgroup_root(&cgrp_dfl_root, &opts);
5611     cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5612 
5613     RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5614 
5615     for_each_subsys(ss, i) {
5616         WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5617              "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5618              i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5619              ss->id, ss->name);
5620         WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5621              "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5622 
5623         ss->id = i;
5624         ss->name = cgroup_subsys_name[i];
5625         if (!ss->legacy_name)
5626             ss->legacy_name = cgroup_subsys_name[i];
5627 
5628         if (ss->early_init)
5629             cgroup_init_subsys(ss, true);
5630     }
5631     return 0;
5632 }
5633 
5634 static u16 cgroup_disable_mask __initdata;
5635 
5636 /**
5637  * cgroup_init - cgroup initialization
5638  *
5639  * Register cgroup filesystem and /proc file, and initialize
5640  * any subsystems that didn't request early init.
5641  */
5642 int __init cgroup_init(void)
5643 {
5644     struct cgroup_subsys *ss;
5645     int ssid;
5646 
5647     BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5648     BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5649     BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5650     BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5651 
5652     /*
5653      * The latency of the synchronize_sched() is too high for cgroups,
5654      * avoid it at the cost of forcing all readers into the slow path.
5655      */
5656     rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5657 
5658     get_user_ns(init_cgroup_ns.user_ns);
5659 
5660     mutex_lock(&cgroup_mutex);
5661 
5662     /*
5663      * Add init_css_set to the hash table so that dfl_root can link to
5664      * it during init.
5665      */
5666     hash_add(css_set_table, &init_css_set.hlist,
5667          css_set_hash(init_css_set.subsys));
5668 
5669     BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5670 
5671     mutex_unlock(&cgroup_mutex);
5672 
5673     for_each_subsys(ss, ssid) {
5674         if (ss->early_init) {
5675             struct cgroup_subsys_state *css =
5676                 init_css_set.subsys[ss->id];
5677 
5678             css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5679                            GFP_KERNEL);
5680             BUG_ON(css->id < 0);
5681         } else {
5682             cgroup_init_subsys(ss, false);
5683         }
5684 
5685         list_add_tail(&init_css_set.e_cset_node[ssid],
5686                   &cgrp_dfl_root.cgrp.e_csets[ssid]);
5687 
5688         /*
5689          * Setting dfl_root subsys_mask needs to consider the
5690          * disabled flag and cftype registration needs kmalloc,
5691          * both of which aren't available during early_init.
5692          */
5693         if (cgroup_disable_mask & (1 << ssid)) {
5694             static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5695             printk(KERN_INFO "Disabling %s control group subsystem\n",
5696                    ss->name);
5697             continue;
5698         }
5699 
5700         if (cgroup_ssid_no_v1(ssid))
5701             printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5702                    ss->name);
5703 
5704         cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5705 
5706         if (ss->implicit_on_dfl)
5707             cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5708         else if (!ss->dfl_cftypes)
5709             cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5710 
5711         if (ss->dfl_cftypes == ss->legacy_cftypes) {
5712             WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5713         } else {
5714             WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5715             WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5716         }
5717 
5718         if (ss->bind)
5719             ss->bind(init_css_set.subsys[ssid]);
5720     }
5721 
5722     /* init_css_set.subsys[] has been updated, re-hash */
5723     hash_del(&init_css_set.hlist);
5724     hash_add(css_set_table, &init_css_set.hlist,
5725          css_set_hash(init_css_set.subsys));
5726 
5727     WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5728     WARN_ON(register_filesystem(&cgroup_fs_type));
5729     WARN_ON(register_filesystem(&cgroup2_fs_type));
5730     WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5731 
5732     return 0;
5733 }
5734 
5735 static int __init cgroup_wq_init(void)
5736 {
5737     /*
5738      * There isn't much point in executing destruction path in
5739      * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5740      * Use 1 for @max_active.
5741      *
5742      * We would prefer to do this in cgroup_init() above, but that
5743      * is called before init_workqueues(): so leave this until after.
5744      */
5745     cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5746     BUG_ON(!cgroup_destroy_wq);
5747 
5748     /*
5749      * Used to destroy pidlists and separate to serve as flush domain.
5750      * Cap @max_active to 1 too.
5751      */
5752     cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5753                             0, 1);
5754     BUG_ON(!cgroup_pidlist_destroy_wq);
5755 
5756     return 0;
5757 }
5758 core_initcall(cgroup_wq_init);
5759 
5760 /*
5761  * proc_cgroup_show()
5762  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5763  *  - Used for /proc/<pid>/cgroup.
5764  */
5765 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5766              struct pid *pid, struct task_struct *tsk)
5767 {
5768     char *buf;
5769     int retval;
5770     struct cgroup_root *root;
5771 
5772     retval = -ENOMEM;
5773     buf = kmalloc(PATH_MAX, GFP_KERNEL);
5774     if (!buf)
5775         goto out;
5776 
5777     mutex_lock(&cgroup_mutex);
5778     spin_lock_irq(&css_set_lock);
5779 
5780     for_each_root(root) {
5781         struct cgroup_subsys *ss;
5782         struct cgroup *cgrp;
5783         int ssid, count = 0;
5784 
5785         if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5786             continue;
5787 
5788         seq_printf(m, "%d:", root->hierarchy_id);
5789         if (root != &cgrp_dfl_root)
5790             for_each_subsys(ss, ssid)
5791                 if (root->subsys_mask & (1 << ssid))
5792                     seq_printf(m, "%s%s", count++ ? "," : "",
5793                            ss->legacy_name);
5794         if (strlen(root->name))
5795             seq_printf(m, "%sname=%s", count ? "," : "",
5796                    root->name);
5797         seq_putc(m, ':');
5798 
5799         cgrp = task_cgroup_from_root(tsk, root);
5800 
5801         /*
5802          * On traditional hierarchies, all zombie tasks show up as
5803          * belonging to the root cgroup.  On the default hierarchy,
5804          * while a zombie doesn't show up in "cgroup.procs" and
5805          * thus can't be migrated, its /proc/PID/cgroup keeps
5806          * reporting the cgroup it belonged to before exiting.  If
5807          * the cgroup is removed before the zombie is reaped,
5808          * " (deleted)" is appended to the cgroup path.
5809          */
5810         if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5811             retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5812                         current->nsproxy->cgroup_ns);
5813             if (retval >= PATH_MAX)
5814                 retval = -ENAMETOOLONG;
5815             if (retval < 0)
5816                 goto out_unlock;
5817 
5818             seq_puts(m, buf);
5819         } else {
5820             seq_puts(m, "/");
5821         }
5822 
5823         if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5824             seq_puts(m, " (deleted)\n");
5825         else
5826             seq_putc(m, '\n');
5827     }
5828 
5829     retval = 0;
5830 out_unlock:
5831     spin_unlock_irq(&css_set_lock);
5832     mutex_unlock(&cgroup_mutex);
5833     kfree(buf);
5834 out:
5835     return retval;
5836 }
5837 
5838 /* Display information about each subsystem and each hierarchy */
5839 static int proc_cgroupstats_show(struct seq_file *m, void *v)
5840 {
5841     struct cgroup_subsys *ss;
5842     int i;
5843 
5844     seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5845     /*
5846      * ideally we don't want subsystems moving around while we do this.
5847      * cgroup_mutex is also necessary to guarantee an atomic snapshot of
5848      * subsys/hierarchy state.
5849      */
5850     mutex_lock(&cgroup_mutex);
5851 
5852     for_each_subsys(ss, i)
5853         seq_printf(m, "%s\t%d\t%d\t%d\n",
5854                ss->legacy_name, ss->root->hierarchy_id,
5855                atomic_read(&ss->root->nr_cgrps),
5856                cgroup_ssid_enabled(i));
5857 
5858     mutex_unlock(&cgroup_mutex);
5859     return 0;
5860 }
5861 
5862 static int cgroupstats_open(struct inode *inode, struct file *file)
5863 {
5864     return single_open(file, proc_cgroupstats_show, NULL);
5865 }
5866 
5867 static const struct file_operations proc_cgroupstats_operations = {
5868     .open = cgroupstats_open,
5869     .read = seq_read,
5870     .llseek = seq_lseek,
5871     .release = single_release,
5872 };
5873 
5874 /**
5875  * cgroup_fork - initialize cgroup related fields during copy_process()
5876  * @child: pointer to task_struct of forking parent process.
5877  *
5878  * A task is associated with the init_css_set until cgroup_post_fork()
5879  * attaches it to the parent's css_set.  Empty cg_list indicates that
5880  * @child isn't holding reference to its css_set.
5881  */
5882 void cgroup_fork(struct task_struct *child)
5883 {
5884     RCU_INIT_POINTER(child->cgroups, &init_css_set);
5885     INIT_LIST_HEAD(&child->cg_list);
5886 }
5887 
5888 /**
5889  * cgroup_can_fork - called on a new task before the process is exposed
5890  * @child: the task in question.
5891  *
5892  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5893  * returns an error, the fork aborts with that error code. This allows for
5894  * a cgroup subsystem to conditionally allow or deny new forks.
5895  */
5896 int cgroup_can_fork(struct task_struct *child)
5897 {
5898     struct cgroup_subsys *ss;
5899     int i, j, ret;
5900 
5901     do_each_subsys_mask(ss, i, have_canfork_callback) {
5902         ret = ss->can_fork(child);
5903         if (ret)
5904             goto out_revert;
5905     } while_each_subsys_mask();
5906 
5907     return 0;
5908 
5909 out_revert:
5910     for_each_subsys(ss, j) {
5911         if (j >= i)
5912             break;
5913         if (ss->cancel_fork)
5914             ss->cancel_fork(child);
5915     }
5916 
5917     return ret;
5918 }
5919 
5920 /**
5921  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5922  * @child: the task in question
5923  *
5924  * This calls the cancel_fork() callbacks if a fork failed *after*
5925  * cgroup_can_fork() succeded.
5926  */
5927 void cgroup_cancel_fork(struct task_struct *child)
5928 {
5929     struct cgroup_subsys *ss;
5930     int i;
5931 
5932     for_each_subsys(ss, i)
5933         if (ss->cancel_fork)
5934             ss->cancel_fork(child);
5935 }
5936 
5937 /**
5938  * cgroup_post_fork - called on a new task after adding it to the task list
5939  * @child: the task in question
5940  *
5941  * Adds the task to the list running through its css_set if necessary and
5942  * call the subsystem fork() callbacks.  Has to be after the task is
5943  * visible on the task list in case we race with the first call to
5944  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5945  * list.
5946  */
5947 void cgroup_post_fork(struct task_struct *child)
5948 {
5949     struct cgroup_subsys *ss;
5950     int i;
5951 
5952     /*
5953      * This may race against cgroup_enable_task_cg_lists().  As that
5954      * function sets use_task_css_set_links before grabbing
5955      * tasklist_lock and we just went through tasklist_lock to add
5956      * @child, it's guaranteed that either we see the set
5957      * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5958      * @child during its iteration.
5959      *
5960      * If we won the race, @child is associated with %current's
5961      * css_set.  Grabbing css_set_lock guarantees both that the
5962      * association is stable, and, on completion of the parent's
5963      * migration, @child is visible in the source of migration or
5964      * already in the destination cgroup.  This guarantee is necessary
5965      * when implementing operations which need to migrate all tasks of
5966      * a cgroup to another.
5967      *
5968      * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5969      * will remain in init_css_set.  This is safe because all tasks are
5970      * in the init_css_set before cg_links is enabled and there's no
5971      * operation which transfers all tasks out of init_css_set.
5972      */
5973     if (use_task_css_set_links) {
5974         struct css_set *cset;
5975 
5976         spin_lock_irq(&css_set_lock);
5977         cset = task_css_set(current);
5978         if (list_empty(&child->cg_list)) {
5979             get_css_set(cset);
5980             css_set_move_task(child, NULL, cset, false);
5981         }
5982         spin_unlock_irq(&css_set_lock);
5983     }
5984 
5985     /*
5986      * Call ss->fork().  This must happen after @child is linked on
5987      * css_set; otherwise, @child might change state between ->fork()
5988      * and addition to css_set.
5989      */
5990     do_each_subsys_mask(ss, i, have_fork_callback) {
5991         ss->fork(child);
5992     } while_each_subsys_mask();
5993 }
5994 
5995 /**
5996  * cgroup_exit - detach cgroup from exiting task
5997  * @tsk: pointer to task_struct of exiting process
5998  *
5999  * Description: Detach cgroup from @tsk and release it.
6000  *
6001  * Note that cgroups marked notify_on_release force every task in
6002  * them to take the global cgroup_mutex mutex when exiting.
6003  * This could impact scaling on very large systems.  Be reluctant to
6004  * use notify_on_release cgroups where very high task exit scaling
6005  * is required on large systems.
6006  *
6007  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6008  * call cgroup_exit() while the task is still competent to handle
6009  * notify_on_release(), then leave the task attached to the root cgroup in
6010  * each hierarchy for the remainder of its exit.  No need to bother with
6011  * init_css_set refcnting.  init_css_set never goes away and we can't race
6012  * with migration path - PF_EXITING is visible to migration path.
6013  */
6014 void cgroup_exit(struct task_struct *tsk)
6015 {
6016     struct cgroup_subsys *ss;
6017     struct css_set *cset;
6018     int i;
6019 
6020     /*
6021      * Unlink from @tsk from its css_set.  As migration path can't race
6022      * with us, we can check css_set and cg_list without synchronization.
6023      */
6024     cset = task_css_set(tsk);
6025 
6026     if (!list_empty(&tsk->cg_list)) {
6027         spin_lock_irq(&css_set_lock);
6028         css_set_move_task(tsk, cset, NULL, false);
6029         spin_unlock_irq(&css_set_lock);
6030     } else {
6031         get_css_set(cset);
6032     }
6033 
6034     /* see cgroup_post_fork() for details */
6035     do_each_subsys_mask(ss, i, have_exit_callback) {
6036         ss->exit(tsk);
6037     } while_each_subsys_mask();
6038 }
6039 
6040 void cgroup_free(struct task_struct *task)
6041 {
6042     struct css_set *cset = task_css_set(task);
6043     struct cgroup_subsys *ss;
6044     int ssid;
6045 
6046     do_each_subsys_mask(ss, ssid, have_free_callback) {
6047         ss->free(task);
6048     } while_each_subsys_mask();
6049 
6050     put_css_set(cset);
6051 }
6052 
6053 static void check_for_release(struct cgroup *cgrp)
6054 {
6055     if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
6056         !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
6057         schedule_work(&cgrp->release_agent_work);
6058 }
6059 
6060 /*
6061  * Notify userspace when a cgroup is released, by running the
6062  * configured release agent with the name of the cgroup (path
6063  * relative to the root of cgroup file system) as the argument.
6064  *
6065  * Most likely, this user command will try to rmdir this cgroup.
6066  *
6067  * This races with the possibility that some other task will be
6068  * attached to this cgroup before it is removed, or that some other
6069  * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
6070  * The presumed 'rmdir' will fail quietly if this cgroup is no longer
6071  * unused, and this cgroup will be reprieved from its death sentence,
6072  * to continue to serve a useful existence.  Next time it's released,
6073  * we will get notified again, if it still has 'notify_on_release' set.
6074  *
6075  * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
6076  * means only wait until the task is successfully execve()'d.  The
6077  * separate release agent task is forked by call_usermodehelper(),
6078  * then control in this thread returns here, without waiting for the
6079  * release agent task.  We don't bother to wait because the caller of
6080  * this routine has no use for the exit status of the release agent
6081  * task, so no sense holding our caller up for that.
6082  */
6083 static void cgroup_release_agent(struct work_struct *work)
6084 {
6085     struct cgroup *cgrp =
6086         container_of(work, struct cgroup, release_agent_work);
6087     char *pathbuf = NULL, *agentbuf = NULL;
6088     char *argv[3], *envp[3];
6089     int ret;
6090 
6091     mutex_lock(&cgroup_mutex);
6092 
6093     pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
6094     agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
6095     if (!pathbuf || !agentbuf)
6096         goto out;
6097 
6098     spin_lock_irq(&css_set_lock);
6099     ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
6100     spin_unlock_irq(&css_set_lock);
6101     if (ret < 0 || ret >= PATH_MAX)
6102         goto out;
6103 
6104     argv[0] = agentbuf;
6105     argv[1] = pathbuf;
6106     argv[2] = NULL;
6107 
6108     /* minimal command environment */
6109     envp[0] = "HOME=/";
6110     envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
6111     envp[2] = NULL;
6112 
6113     mutex_unlock(&cgroup_mutex);
6114     call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
6115     goto out_free;
6116 out:
6117     mutex_unlock(&cgroup_mutex);
6118 out_free:
6119     kfree(agentbuf);
6120     kfree(pathbuf);
6121 }
6122 
6123 static int __init cgroup_disable(char *str)
6124 {
6125     struct cgroup_subsys *ss;
6126     char *token;
6127     int i;
6128 
6129     while ((token = strsep(&str, ",")) != NULL) {
6130         if (!*token)
6131             continue;
6132 
6133         for_each_subsys(ss, i) {
6134             if (strcmp(token, ss->name) &&
6135                 strcmp(token, ss->legacy_name))
6136                 continue;
6137             cgroup_disable_mask |= 1 << i;
6138         }
6139     }
6140     return 1;
6141 }
6142 __setup("cgroup_disable=", cgroup_disable);
6143 
6144 static int __init cgroup_no_v1(char *str)
6145 {
6146     struct cgroup_subsys *ss;
6147     char *token;
6148     int i;
6149 
6150     while ((token = strsep(&str, ",")) != NULL) {
6151         if (!*token)
6152             continue;
6153 
6154         if (!strcmp(token, "all")) {
6155             cgroup_no_v1_mask = U16_MAX;
6156             break;
6157         }
6158 
6159         for_each_subsys(ss, i) {
6160             if (strcmp(token, ss->name) &&
6161                 strcmp(token, ss->legacy_name))
6162                 continue;
6163 
6164             cgroup_no_v1_mask |= 1 << i;
6165         }
6166     }
6167     return 1;
6168 }
6169 __setup("cgroup_no_v1=", cgroup_no_v1);
6170 
6171 /**
6172  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6173  * @dentry: directory dentry of interest
6174  * @ss: subsystem of interest
6175  *
6176  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6177  * to get the corresponding css and return it.  If such css doesn't exist
6178  * or can't be pinned, an ERR_PTR value is returned.
6179  */
6180 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6181                                struct cgroup_subsys *ss)
6182 {
6183     struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6184     struct file_system_type *s_type = dentry->d_sb->s_type;
6185     struct cgroup_subsys_state *css = NULL;
6186     struct cgroup *cgrp;
6187 
6188     /* is @dentry a cgroup dir? */
6189     if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6190         !kn || kernfs_type(kn) != KERNFS_DIR)
6191         return ERR_PTR(-EBADF);
6192 
6193     rcu_read_lock();
6194 
6195     /*
6196      * This path doesn't originate from kernfs and @kn could already
6197      * have been or be removed at any point.  @kn->priv is RCU
6198      * protected for this access.  See css_release_work_fn() for details.
6199      */
6200     cgrp = rcu_dereference(kn->priv);
6201     if (cgrp)
6202         css = cgroup_css(cgrp, ss);
6203 
6204     if (!css || !css_tryget_online(css))
6205         css = ERR_PTR(-ENOENT);
6206 
6207     rcu_read_unlock();
6208     return css;
6209 }
6210 
6211 /**
6212  * css_from_id - lookup css by id
6213  * @id: the cgroup id
6214  * @ss: cgroup subsys to be looked into
6215  *
6216  * Returns the css if there's valid one with @id, otherwise returns NULL.
6217  * Should be called under rcu_read_lock().
6218  */
6219 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6220 {
6221     WARN_ON_ONCE(!rcu_read_lock_held());
6222     return idr_find(&ss->css_idr, id);
6223 }
6224 
6225 /**
6226  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6227  * @path: path on the default hierarchy
6228  *
6229  * Find the cgroup at @path on the default hierarchy, increment its
6230  * reference count and return it.  Returns pointer to the found cgroup on
6231  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6232  * if @path points to a non-directory.
6233  */
6234 struct cgroup *cgroup_get_from_path(const char *path)
6235 {
6236     struct kernfs_node *kn;
6237     struct cgroup *cgrp;
6238 
6239     mutex_lock(&cgroup_mutex);
6240 
6241     kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6242     if (kn) {
6243         if (kernfs_type(kn) == KERNFS_DIR) {
6244             cgrp = kn->priv;
6245             cgroup_get(cgrp);
6246         } else {
6247             cgrp = ERR_PTR(-ENOTDIR);
6248         }
6249         kernfs_put(kn);
6250     } else {
6251         cgrp = ERR_PTR(-ENOENT);
6252     }
6253 
6254     mutex_unlock(&cgroup_mutex);
6255     return cgrp;
6256 }
6257 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6258 
6259 /**
6260  * cgroup_get_from_fd - get a cgroup pointer from a fd
6261  * @fd: fd obtained by open(cgroup2_dir)
6262  *
6263  * Find the cgroup from a fd which should be obtained
6264  * by opening a cgroup directory.  Returns a pointer to the
6265  * cgroup on success. ERR_PTR is returned if the cgroup
6266  * cannot be found.
6267  */
6268 struct cgroup *cgroup_get_from_fd(int fd)
6269 {
6270     struct cgroup_subsys_state *css;
6271     struct cgroup *cgrp;
6272     struct file *f;
6273 
6274     f = fget_raw(fd);
6275     if (!f)
6276         return ERR_PTR(-EBADF);
6277 
6278     css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6279     fput(f);
6280     if (IS_ERR(css))
6281         return ERR_CAST(css);
6282 
6283     cgrp = css->cgroup;
6284     if (!cgroup_on_dfl(cgrp)) {
6285         cgroup_put(cgrp);
6286         return ERR_PTR(-EBADF);
6287     }
6288 
6289     return cgrp;
6290 }
6291 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6292 
6293 /*
6294  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6295  * definition in cgroup-defs.h.
6296  */
6297 #ifdef CONFIG_SOCK_CGROUP_DATA
6298 
6299 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6300 
6301 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6302 static bool cgroup_sk_alloc_disabled __read_mostly;
6303 
6304 void cgroup_sk_alloc_disable(void)
6305 {
6306     if (cgroup_sk_alloc_disabled)
6307         return;
6308     pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6309     cgroup_sk_alloc_disabled = true;
6310 }
6311 
6312 #else
6313 
6314 #define cgroup_sk_alloc_disabled    false
6315 
6316 #endif
6317 
6318 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6319 {
6320     if (cgroup_sk_alloc_disabled)
6321         return;
6322 
6323     /* Socket clone path */
6324     if (skcd->val) {
6325         cgroup_get(sock_cgroup_ptr(skcd));
6326         return;
6327     }
6328 
6329     rcu_read_lock();
6330 
6331     while (true) {
6332         struct css_set *cset;
6333 
6334         cset = task_css_set(current);
6335         if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6336             skcd->val = (unsigned long)cset->dfl_cgrp;
6337             break;
6338         }
6339         cpu_relax();
6340     }
6341 
6342     rcu_read_unlock();
6343 }
6344 
6345 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6346 {
6347     cgroup_put(sock_cgroup_ptr(skcd));
6348 }
6349 
6350 #endif  /* CONFIG_SOCK_CGROUP_DATA */
6351 
6352 /* cgroup namespaces */
6353 
6354 static struct ucounts *inc_cgroup_namespaces(struct user_namespace *ns)
6355 {
6356     return inc_ucount(ns, current_euid(), UCOUNT_CGROUP_NAMESPACES);
6357 }
6358 
6359 static void dec_cgroup_namespaces(struct ucounts *ucounts)
6360 {
6361     dec_ucount(ucounts, UCOUNT_CGROUP_NAMESPACES);
6362 }
6363 
6364 static struct cgroup_namespace *alloc_cgroup_ns(void)
6365 {
6366     struct cgroup_namespace *new_ns;
6367     int ret;
6368 
6369     new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
6370     if (!new_ns)
6371         return ERR_PTR(-ENOMEM);
6372     ret = ns_alloc_inum(&new_ns->ns);
6373     if (ret) {
6374         kfree(new_ns);
6375         return ERR_PTR(ret);
6376     }
6377     atomic_set(&new_ns->count, 1);
6378     new_ns->ns.ops = &cgroupns_operations;
6379     return new_ns;
6380 }
6381 
6382 void free_cgroup_ns(struct cgroup_namespace *ns)
6383 {
6384     put_css_set(ns->root_cset);
6385     dec_cgroup_namespaces(ns->ucounts);
6386     put_user_ns(ns->user_ns);
6387     ns_free_inum(&ns->ns);
6388     kfree(ns);
6389 }
6390 EXPORT_SYMBOL(free_cgroup_ns);
6391 
6392 struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
6393                     struct user_namespace *user_ns,
6394                     struct cgroup_namespace *old_ns)
6395 {
6396     struct cgroup_namespace *new_ns;
6397     struct ucounts *ucounts;
6398     struct css_set *cset;
6399 
6400     BUG_ON(!old_ns);
6401 
6402     if (!(flags & CLONE_NEWCGROUP)) {
6403         get_cgroup_ns(old_ns);
6404         return old_ns;
6405     }
6406 
6407     /* Allow only sysadmin to create cgroup namespace. */
6408     if (!ns_capable(user_ns, CAP_SYS_ADMIN))
6409         return ERR_PTR(-EPERM);
6410 
6411     ucounts = inc_cgroup_namespaces(user_ns);
6412     if (!ucounts)
6413         return ERR_PTR(-ENOSPC);
6414 
6415     /* It is not safe to take cgroup_mutex here */
6416     spin_lock_irq(&css_set_lock);
6417     cset = task_css_set(current);
6418     get_css_set(cset);
6419     spin_unlock_irq(&css_set_lock);
6420 
6421     new_ns = alloc_cgroup_ns();
6422     if (IS_ERR(new_ns)) {
6423         put_css_set(cset);
6424         dec_cgroup_namespaces(ucounts);
6425         return new_ns;
6426     }
6427 
6428     new_ns->user_ns = get_user_ns(user_ns);
6429     new_ns->ucounts = ucounts;
6430     new_ns->root_cset = cset;
6431 
6432     return new_ns;
6433 }
6434 
6435 static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
6436 {
6437     return container_of(ns, struct cgroup_namespace, ns);
6438 }
6439 
6440 static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
6441 {
6442     struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
6443 
6444     if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
6445         !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
6446         return -EPERM;
6447 
6448     /* Don't need to do anything if we are attaching to our own cgroupns. */
6449     if (cgroup_ns == nsproxy->cgroup_ns)
6450         return 0;
6451 
6452     get_cgroup_ns(cgroup_ns);
6453     put_cgroup_ns(nsproxy->cgroup_ns);
6454     nsproxy->cgroup_ns = cgroup_ns;
6455 
6456     return 0;
6457 }
6458 
6459 static struct ns_common *cgroupns_get(struct task_struct *task)
6460 {
6461     struct cgroup_namespace *ns = NULL;
6462     struct nsproxy *nsproxy;
6463 
6464     task_lock(task);
6465     nsproxy = task->nsproxy;
6466     if (nsproxy) {
6467         ns = nsproxy->cgroup_ns;
6468         get_cgroup_ns(ns);
6469     }
6470     task_unlock(task);
6471 
6472     return ns ? &ns->ns : NULL;
6473 }
6474 
6475 static void cgroupns_put(struct ns_common *ns)
6476 {
6477     put_cgroup_ns(to_cg_ns(ns));
6478 }
6479 
6480 static struct user_namespace *cgroupns_owner(struct ns_common *ns)
6481 {
6482     return to_cg_ns(ns)->user_ns;
6483 }
6484 
6485 const struct proc_ns_operations cgroupns_operations = {
6486     .name       = "cgroup",
6487     .type       = CLONE_NEWCGROUP,
6488     .get        = cgroupns_get,
6489     .put        = cgroupns_put,
6490     .install    = cgroupns_install,
6491     .owner      = cgroupns_owner,
6492 };
6493 
6494 static __init int cgroup_namespaces_init(void)
6495 {
6496     return 0;
6497 }
6498 subsys_initcall(cgroup_namespaces_init);
6499 
6500 #ifdef CONFIG_CGROUP_BPF
6501 int cgroup_bpf_update(struct cgroup *cgrp, struct bpf_prog *prog,
6502               enum bpf_attach_type type, bool overridable)
6503 {
6504     struct cgroup *parent = cgroup_parent(cgrp);
6505     int ret;
6506 
6507     mutex_lock(&cgroup_mutex);
6508     ret = __cgroup_bpf_update(cgrp, parent, prog, type, overridable);
6509     mutex_unlock(&cgroup_mutex);
6510     return ret;
6511 }
6512 #endif /* CONFIG_CGROUP_BPF */
6513 
6514 #ifdef CONFIG_CGROUP_DEBUG
6515 static struct cgroup_subsys_state *
6516 debug_css_alloc(struct cgroup_subsys_state *parent_css)
6517 {
6518     struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
6519 
6520     if (!css)
6521         return ERR_PTR(-ENOMEM);
6522 
6523     return css;
6524 }
6525 
6526 static void debug_css_free(struct cgroup_subsys_state *css)
6527 {
6528     kfree(css);
6529 }
6530 
6531 static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
6532                 struct cftype *cft)
6533 {
6534     return cgroup_task_count(css->cgroup);
6535 }
6536 
6537 static u64 current_css_set_read(struct cgroup_subsys_state *css,
6538                 struct cftype *cft)
6539 {
6540     return (u64)(unsigned long)current->cgroups;
6541 }
6542 
6543 static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
6544                      struct cftype *cft)
6545 {
6546     u64 count;
6547 
6548     rcu_read_lock();
6549     count = atomic_read(&task_css_set(current)->refcount);
6550     rcu_read_unlock();
6551     return count;
6552 }
6553 
6554 static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
6555 {
6556     struct cgrp_cset_link *link;
6557     struct css_set *cset;
6558     char *name_buf;
6559 
6560     name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
6561     if (!name_buf)
6562         return -ENOMEM;
6563 
6564     spin_lock_irq(&css_set_lock);
6565     rcu_read_lock();
6566     cset = rcu_dereference(current->cgroups);
6567     list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
6568         struct cgroup *c = link->cgrp;
6569 
6570         cgroup_name(c, name_buf, NAME_MAX + 1);
6571         seq_printf(seq, "Root %d group %s\n",
6572                c->root->hierarchy_id, name_buf);
6573     }
6574     rcu_read_unlock();
6575     spin_unlock_irq(&css_set_lock);
6576     kfree(name_buf);
6577     return 0;
6578 }
6579 
6580 #define MAX_TASKS_SHOWN_PER_CSS 25
6581 static int cgroup_css_links_read(struct seq_file *seq, void *v)
6582 {
6583     struct cgroup_subsys_state *css = seq_css(seq);
6584     struct cgrp_cset_link *link;
6585 
6586     spin_lock_irq(&css_set_lock);
6587     list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
6588         struct css_set *cset = link->cset;
6589         struct task_struct *task;
6590         int count = 0;
6591 
6592         seq_printf(seq, "css_set %p\n", cset);
6593 
6594         list_for_each_entry(task, &cset->tasks, cg_list) {
6595             if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6596                 goto overflow;
6597             seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6598         }
6599 
6600         list_for_each_entry(task, &cset->mg_tasks, cg_list) {
6601             if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6602                 goto overflow;
6603             seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6604         }
6605         continue;
6606     overflow:
6607         seq_puts(seq, "  ...\n");
6608     }
6609     spin_unlock_irq(&css_set_lock);
6610     return 0;
6611 }
6612 
6613 static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
6614 {
6615     return (!cgroup_is_populated(css->cgroup) &&
6616         !css_has_online_children(&css->cgroup->self));
6617 }
6618 
6619 static struct cftype debug_files[] =  {
6620     {
6621         .name = "taskcount",
6622         .read_u64 = debug_taskcount_read,
6623     },
6624 
6625     {
6626         .name = "current_css_set",
6627         .read_u64 = current_css_set_read,
6628     },
6629 
6630     {
6631         .name = "current_css_set_refcount",
6632         .read_u64 = current_css_set_refcount_read,
6633     },
6634 
6635     {
6636         .name = "current_css_set_cg_links",
6637         .seq_show = current_css_set_cg_links_read,
6638     },
6639 
6640     {
6641         .name = "cgroup_css_links",
6642         .seq_show = cgroup_css_links_read,
6643     },
6644 
6645     {
6646         .name = "releasable",
6647         .read_u64 = releasable_read,
6648     },
6649 
6650     { } /* terminate */
6651 };
6652 
6653 struct cgroup_subsys debug_cgrp_subsys = {
6654     .css_alloc = debug_css_alloc,
6655     .css_free = debug_css_free,
6656     .legacy_cftypes = debug_files,
6657 };
6658 #endif /* CONFIG_CGROUP_DEBUG */