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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * kernel/workqueue.c - generic async execution with shared worker pool
  *
  * Copyright (C) 2002       Ingo Molnar
  *
  *   Derived from the taskqueue/keventd code by:
  *     David Woodhouse <dwmw2@infradead.org>
  *     Andrew Morton
  *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
  *     Theodore Ts'o <tytso@mit.edu>
  *
  * Made to use alloc_percpu by Christoph Lameter.
  *
  * Copyright (C) 2010       SUSE Linux Products GmbH
  * Copyright (C) 2010       Tejun Heo <tj@kernel.org>
  *
  * This is the generic async execution mechanism.  Work items as are
  * executed in process context.  The worker pool is shared and
  * automatically managed.  There are two worker pools for each CPU (one for
  * normal work items and the other for high priority ones) and some extra
  * pools for workqueues which are not bound to any specific CPU - the
  * number of these backing pools is dynamic.
  *
  * Please read Documentation/core-api/workqueue.rst for details.
  */
 
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/init.h>
 #include <linux/signal.h>
 #include <linux/completion.h>
 #include <linux/workqueue.h>
 #include <linux/slab.h>
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/kthread.h>
 #include <linux/hardirq.h>
 #include <linux/mempolicy.h>
 #include <linux/freezer.h>
 #include <linux/debug_locks.h>
 #include <linux/lockdep.h>
 #include <linux/idr.h>
 #include <linux/jhash.h>
 #include <linux/hashtable.h>
 #include <linux/rculist.h>
 #include <linux/nodemask.h>
 #include <linux/moduleparam.h>
 #include <linux/uaccess.h>
 #include <linux/sched/isolation.h>
 #include <linux/nmi.h>
 #include <linux/kvm_para.h>
 
 #include "workqueue_internal.h"
 
 enum {
     /*
      * worker_pool flags
      *
      * A bound pool is either associated or disassociated with its CPU.
      * While associated (!DISASSOCIATED), all workers are bound to the
      * CPU and none has %WORKER_UNBOUND set and concurrency management
      * is in effect.
      *
      * While DISASSOCIATED, the cpu may be offline and all workers have
      * %WORKER_UNBOUND set and concurrency management disabled, and may
      * be executing on any CPU.  The pool behaves as an unbound one.
      *
      * Note that DISASSOCIATED should be flipped only while holding
      * wq_pool_attach_mutex to avoid changing binding state while
      * worker_attach_to_pool() is in progress.
      */
     POOL_MANAGER_ACTIVE = 1 << 0,   /* being managed */
     POOL_DISASSOCIATED  = 1 << 2,   /* cpu can't serve workers */
 
     /* worker flags */
     WORKER_DIE      = 1 << 1,   /* die die die */
     WORKER_IDLE     = 1 << 2,   /* is idle */
     WORKER_PREP     = 1 << 3,   /* preparing to run works */
     WORKER_CPU_INTENSIVE    = 1 << 6,   /* cpu intensive */
     WORKER_UNBOUND      = 1 << 7,   /* worker is unbound */
     WORKER_REBOUND      = 1 << 8,   /* worker was rebound */
 
     WORKER_NOT_RUNNING  = WORKER_PREP | WORKER_CPU_INTENSIVE |
                   WORKER_UNBOUND | WORKER_REBOUND,
 
     NR_STD_WORKER_POOLS = 2,        /* # standard pools per cpu */
 
     UNBOUND_POOL_HASH_ORDER = 6,        /* hashed by pool->attrs */
     BUSY_WORKER_HASH_ORDER  = 6,        /* 64 pointers */
 
     MAX_IDLE_WORKERS_RATIO  = 4,        /* 1/4 of busy can be idle */
     IDLE_WORKER_TIMEOUT = 300 * HZ, /* keep idle ones for 5 mins */
 
     MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
                         /* call for help after 10ms
                            (min two ticks) */
     MAYDAY_INTERVAL     = HZ / 10,  /* and then every 100ms */
     CREATE_COOLDOWN     = HZ,       /* time to breath after fail */
 
     /*
      * Rescue workers are used only on emergencies and shared by
      * all cpus.  Give MIN_NICE.
      */
     RESCUER_NICE_LEVEL  = MIN_NICE,
     HIGHPRI_NICE_LEVEL  = MIN_NICE,
 
     WQ_NAME_LEN     = 24,
 };
 
 /*
  * Structure fields follow one of the following exclusion rules.
  *
  * I: Modifiable by initialization/destruction paths and read-only for
  *    everyone else.
  *
  * P: Preemption protected.  Disabling preemption is enough and should
  *    only be modified and accessed from the local cpu.
  *
  * L: pool->lock protected.  Access with pool->lock held.
  *
  * X: During normal operation, modification requires pool->lock and should
  *    be done only from local cpu.  Either disabling preemption on local
  *    cpu or grabbing pool->lock is enough for read access.  If
  *    POOL_DISASSOCIATED is set, it's identical to L.
  *
  * A: wq_pool_attach_mutex protected.
  *
  * PL: wq_pool_mutex protected.
  *
  * PR: wq_pool_mutex protected for writes.  RCU protected for reads.
  *
  * PW: wq_pool_mutex and wq->mutex protected for writes.  Either for reads.
  *
  * PWR: wq_pool_mutex and wq->mutex protected for writes.  Either or
  *      RCU for reads.
  *
  * WQ: wq->mutex protected.
  *
  * WR: wq->mutex protected for writes.  RCU protected for reads.
  *
  * MD: wq_mayday_lock protected.
  */
 
 /* struct worker is defined in workqueue_internal.h */
 
 struct worker_pool {
     raw_spinlock_t      lock;       /* the pool lock */
     int         cpu;        /* I: the associated cpu */
     int         node;       /* I: the associated node ID */
     int         id;     /* I: pool ID */
     unsigned int        flags;      /* X: flags */
 
     unsigned long       watchdog_ts;    /* L: watchdog timestamp */
 
     /*
      * The counter is incremented in a process context on the associated CPU
      * w/ preemption disabled, and decremented or reset in the same context
      * but w/ pool->lock held. The readers grab pool->lock and are
      * guaranteed to see if the counter reached zero.
      */
     int         nr_running;
 
     struct list_head    worklist;   /* L: list of pending works */
 
     int         nr_workers; /* L: total number of workers */
     int         nr_idle;    /* L: currently idle workers */
 
     struct list_head    idle_list;  /* L: list of idle workers */
     struct timer_list   idle_timer; /* L: worker idle timeout */
     struct timer_list   mayday_timer;   /* L: SOS timer for workers */
 
     /* a workers is either on busy_hash or idle_list, or the manager */
     DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
                         /* L: hash of busy workers */
 
     struct worker       *manager;   /* L: purely informational */
     struct list_head    workers;    /* A: attached workers */
     struct completion   *detach_completion; /* all workers detached */
 
     struct ida      worker_ida; /* worker IDs for task name */
 
     struct workqueue_attrs  *attrs;     /* I: worker attributes */
     struct hlist_node   hash_node;  /* PL: unbound_pool_hash node */
     int         refcnt;     /* PL: refcnt for unbound pools */
 
     /*
      * Destruction of pool is RCU protected to allow dereferences
      * from get_work_pool().
      */
     struct rcu_head     rcu;
 };
 
 /*
  * The per-pool workqueue.  While queued, the lower WORK_STRUCT_FLAG_BITS
  * of work_struct->data are used for flags and the remaining high bits
  * point to the pwq; thus, pwqs need to be aligned at two's power of the
  * number of flag bits.
  */
 struct pool_workqueue {
     struct worker_pool  *pool;      /* I: the associated pool */
     struct workqueue_struct *wq;        /* I: the owning workqueue */
     int         work_color; /* L: current color */
     int         flush_color;    /* L: flushing color */
     int         refcnt;     /* L: reference count */
     int         nr_in_flight[WORK_NR_COLORS];
                         /* L: nr of in_flight works */
 
     /*
      * nr_active management and WORK_STRUCT_INACTIVE:
      *
      * When pwq->nr_active >= max_active, new work item is queued to
      * pwq->inactive_works instead of pool->worklist and marked with
      * WORK_STRUCT_INACTIVE.
      *
      * All work items marked with WORK_STRUCT_INACTIVE do not participate
      * in pwq->nr_active and all work items in pwq->inactive_works are
      * marked with WORK_STRUCT_INACTIVE.  But not all WORK_STRUCT_INACTIVE
      * work items are in pwq->inactive_works.  Some of them are ready to
      * run in pool->worklist or worker->scheduled.  Those work itmes are
      * only struct wq_barrier which is used for flush_work() and should
      * not participate in pwq->nr_active.  For non-barrier work item, it
      * is marked with WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works.
      */
     int         nr_active;  /* L: nr of active works */
     int         max_active; /* L: max active works */
     struct list_head    inactive_works; /* L: inactive works */
     struct list_head    pwqs_node;  /* WR: node on wq->pwqs */
     struct list_head    mayday_node;    /* MD: node on wq->maydays */
 
     /*
      * Release of unbound pwq is punted to system_wq.  See put_pwq()
      * and pwq_unbound_release_workfn() for details.  pool_workqueue
      * itself is also RCU protected so that the first pwq can be
      * determined without grabbing wq->mutex.
      */
     struct work_struct  unbound_release_work;
     struct rcu_head     rcu;
 } __aligned(1 << WORK_STRUCT_FLAG_BITS);
 
 /*
  * Structure used to wait for workqueue flush.
  */
 struct wq_flusher {
     struct list_head    list;       /* WQ: list of flushers */
     int         flush_color;    /* WQ: flush color waiting for */
     struct completion   done;       /* flush completion */
 };
 
 struct wq_device;
 
 /*
  * The externally visible workqueue.  It relays the issued work items to
  * the appropriate worker_pool through its pool_workqueues.
  */
 struct workqueue_struct {
     struct list_head    pwqs;       /* WR: all pwqs of this wq */
     struct list_head    list;       /* PR: list of all workqueues */
 
     struct mutex        mutex;      /* protects this wq */
     int         work_color; /* WQ: current work color */
     int         flush_color;    /* WQ: current flush color */
     atomic_t        nr_pwqs_to_flush; /* flush in progress */
     struct wq_flusher   *first_flusher; /* WQ: first flusher */
     struct list_head    flusher_queue;  /* WQ: flush waiters */
     struct list_head    flusher_overflow; /* WQ: flush overflow list */
 
     struct list_head    maydays;    /* MD: pwqs requesting rescue */
     struct worker       *rescuer;   /* MD: rescue worker */
 
     int         nr_drainers;    /* WQ: drain in progress */
     int         saved_max_active; /* WQ: saved pwq max_active */
 
     struct workqueue_attrs  *unbound_attrs; /* PW: only for unbound wqs */
     struct pool_workqueue   *dfl_pwq;   /* PW: only for unbound wqs */
 
 #ifdef CONFIG_SYSFS
     struct wq_device    *wq_dev;    /* I: for sysfs interface */
 #endif
 #ifdef CONFIG_LOCKDEP
     char            *lock_name;
     struct lock_class_key   key;
     struct lockdep_map  lockdep_map;
 #endif
     char            name[WQ_NAME_LEN]; /* I: workqueue name */
 
     /*
      * Destruction of workqueue_struct is RCU protected to allow walking
      * the workqueues list without grabbing wq_pool_mutex.
      * This is used to dump all workqueues from sysrq.
      */
     struct rcu_head     rcu;
 
     /* hot fields used during command issue, aligned to cacheline */
     unsigned int        flags ____cacheline_aligned; /* WQ: WQ_* flags */
     struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
     struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
 };
 
 static struct kmem_cache *pwq_cache;
 
 static cpumask_var_t *wq_numa_possible_cpumask;
                     /* possible CPUs of each node */
 
 static bool wq_disable_numa;
 module_param_named(disable_numa, wq_disable_numa, bool, 0444);
 
 /* see the comment above the definition of WQ_POWER_EFFICIENT */
 static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
 module_param_named(power_efficient, wq_power_efficient, bool, 0444);
 
 static bool wq_online;          /* can kworkers be created yet? */
 
 static bool wq_numa_enabled;        /* unbound NUMA affinity enabled */
 
 /* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */
 static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
 
 static DEFINE_MUTEX(wq_pool_mutex); /* protects pools and workqueues list */
 static DEFINE_MUTEX(wq_pool_attach_mutex); /* protects worker attach/detach */
 static DEFINE_RAW_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
 /* wait for manager to go away */
 static struct rcuwait manager_wait = __RCUWAIT_INITIALIZER(manager_wait);
 
 static LIST_HEAD(workqueues);       /* PR: list of all workqueues */
 static bool workqueue_freezing;     /* PL: have wqs started freezing? */
 
 /* PL: allowable cpus for unbound wqs and work items */
 static cpumask_var_t wq_unbound_cpumask;
 
 /* CPU where unbound work was last round robin scheduled from this CPU */
 static DEFINE_PER_CPU(int, wq_rr_cpu_last);
 
 /*
  * Local execution of unbound work items is no longer guaranteed.  The
  * following always forces round-robin CPU selection on unbound work items
  * to uncover usages which depend on it.
  */
 #ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
 static bool wq_debug_force_rr_cpu = true;
 #else
 static bool wq_debug_force_rr_cpu = false;
 #endif
 module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
 
 /* the per-cpu worker pools */
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], cpu_worker_pools);
 
 static DEFINE_IDR(worker_pool_idr); /* PR: idr of all pools */
 
 /* PL: hash of all unbound pools keyed by pool->attrs */
 static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
 
 /* I: attributes used when instantiating standard unbound pools on demand */
 static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
 
 /* I: attributes used when instantiating ordered pools on demand */
 static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
 
 struct workqueue_struct *system_wq __read_mostly;
 EXPORT_SYMBOL(system_wq);
 struct workqueue_struct *system_highpri_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_highpri_wq);
 struct workqueue_struct *system_long_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_long_wq);
 struct workqueue_struct *system_unbound_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_unbound_wq);
 struct workqueue_struct *system_freezable_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_freezable_wq);
 struct workqueue_struct *system_power_efficient_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_power_efficient_wq);
 struct workqueue_struct *system_freezable_power_efficient_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
 
 static int worker_thread(void *__worker);
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 static void show_pwq(struct pool_workqueue *pwq);
 static void show_one_worker_pool(struct worker_pool *pool);
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/workqueue.h>
 
 #define assert_rcu_or_pool_mutex()                  \
     RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&           \
              !lockdep_is_held(&wq_pool_mutex),      \
              "RCU or wq_pool_mutex should be held")
 
 #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)            \
     RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&           \
              !lockdep_is_held(&wq->mutex) &&        \
              !lockdep_is_held(&wq_pool_mutex),      \
              "RCU, wq->mutex or wq_pool_mutex should be held")
 
 #define for_each_cpu_worker_pool(pool, cpu)             \
     for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];       \
          (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
          (pool)++)
 
 /**
  * for_each_pool - iterate through all worker_pools in the system
  * @pool: iteration cursor
  * @pi: integer used for iteration
  *
  * This must be called either with wq_pool_mutex held or RCU read
  * locked.  If the pool needs to be used beyond the locking in effect, the
  * caller is responsible for guaranteeing that the pool stays online.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pool(pool, pi)                     \
     idr_for_each_entry(&worker_pool_idr, pool, pi)          \
         if (({ assert_rcu_or_pool_mutex(); false; })) { }   \
         else
 
 /**
  * for_each_pool_worker - iterate through all workers of a worker_pool
  * @worker: iteration cursor
  * @pool: worker_pool to iterate workers of
  *
  * This must be called with wq_pool_attach_mutex.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pool_worker(worker, pool)              \
     list_for_each_entry((worker), &(pool)->workers, node)       \
         if (({ lockdep_assert_held(&wq_pool_attach_mutex); false; })) { } \
         else
 
 /**
  * for_each_pwq - iterate through all pool_workqueues of the specified workqueue
  * @pwq: iteration cursor
  * @wq: the target workqueue
  *
  * This must be called either with wq->mutex held or RCU read locked.
  * If the pwq needs to be used beyond the locking in effect, the caller is
  * responsible for guaranteeing that the pwq stays online.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pwq(pwq, wq)                       \
     list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,      \
                  lockdep_is_held(&(wq->mutex)))
 
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
 
 static const struct debug_obj_descr work_debug_descr;
 
 static void *work_debug_hint(void *addr)
 {
     return ((struct work_struct *) addr)->func;
 }
 
 static bool work_is_static_object(void *addr)
 {
     struct work_struct *work = addr;
 
     return test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work));
 }
 
 /*
  * fixup_init is called when:
  * - an active object is initialized
  */
 static bool work_fixup_init(void *addr, enum debug_obj_state state)
 {
     struct work_struct *work = addr;
 
     switch (state) {
     case ODEBUG_STATE_ACTIVE:
         cancel_work_sync(work);
         debug_object_init(work, &work_debug_descr);
         return true;
     default:
         return false;
     }
 }
 
 /*
  * fixup_free is called when:
  * - an active object is freed
  */
 static bool work_fixup_free(void *addr, enum debug_obj_state state)
 {
     struct work_struct *work = addr;
 
     switch (state) {
     case ODEBUG_STATE_ACTIVE:
         cancel_work_sync(work);
         debug_object_free(work, &work_debug_descr);
         return true;
     default:
         return false;
     }
 }
 
 static const struct debug_obj_descr work_debug_descr = {
     .name       = "work_struct",
     .debug_hint = work_debug_hint,
     .is_static_object = work_is_static_object,
     .fixup_init = work_fixup_init,
     .fixup_free = work_fixup_free,
 };
 
 static inline void debug_work_activate(struct work_struct *work)
 {
     debug_object_activate(work, &work_debug_descr);
 }
 
 static inline void debug_work_deactivate(struct work_struct *work)
 {
     debug_object_deactivate(work, &work_debug_descr);
 }
 
 void __init_work(struct work_struct *work, int onstack)
 {
     if (onstack)
         debug_object_init_on_stack(work, &work_debug_descr);
     else
         debug_object_init(work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(__init_work);
 
 void destroy_work_on_stack(struct work_struct *work)
 {
     debug_object_free(work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_work_on_stack);
 
 void destroy_delayed_work_on_stack(struct delayed_work *work)
 {
     destroy_timer_on_stack(&work->timer);
     debug_object_free(&work->work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);
 
 #else
 static inline void debug_work_activate(struct work_struct *work) { }
 static inline void debug_work_deactivate(struct work_struct *work) { }
 #endif
 
 /**
  * worker_pool_assign_id - allocate ID and assign it to @pool
  * @pool: the pool pointer of interest
  *
  * Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
  * successfully, -errno on failure.
  */
 static int worker_pool_assign_id(struct worker_pool *pool)
 {
     int ret;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
             GFP_KERNEL);
     if (ret >= 0) {
         pool->id = ret;
         return 0;
     }
     return ret;
 }
 
 /**
  * unbound_pwq_by_node - return the unbound pool_workqueue for the given node
  * @wq: the target workqueue
  * @node: the node ID
  *
  * This must be called with any of wq_pool_mutex, wq->mutex or RCU
  * read locked.
  * If the pwq needs to be used beyond the locking in effect, the caller is
  * responsible for guaranteeing that the pwq stays online.
  *
  * Return: The unbound pool_workqueue for @node.
  */
 static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
                           int node)
 {
     assert_rcu_or_wq_mutex_or_pool_mutex(wq);
 
     /*
      * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
      * delayed item is pending.  The plan is to keep CPU -> NODE
      * mapping valid and stable across CPU on/offlines.  Once that
      * happens, this workaround can be removed.
      */
     if (unlikely(node == NUMA_NO_NODE))
         return wq->dfl_pwq;
 
     return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
 }
 
 static unsigned int work_color_to_flags(int color)
 {
     return color << WORK_STRUCT_COLOR_SHIFT;
 }
 
 static int get_work_color(unsigned long work_data)
 {
     return (work_data >> WORK_STRUCT_COLOR_SHIFT) &
         ((1 << WORK_STRUCT_COLOR_BITS) - 1);
 }
 
 static int work_next_color(int color)
 {
     return (color + 1) % WORK_NR_COLORS;
 }
 
 /*
  * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
  * contain the pointer to the queued pwq.  Once execution starts, the flag
  * is cleared and the high bits contain OFFQ flags and pool ID.
  *
  * set_work_pwq(), set_work_pool_and_clear_pending(), mark_work_canceling()
  * and clear_work_data() can be used to set the pwq, pool or clear
  * work->data.  These functions should only be called while the work is
  * owned - ie. while the PENDING bit is set.
  *
  * get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
  * corresponding to a work.  Pool is available once the work has been
  * queued anywhere after initialization until it is sync canceled.  pwq is
  * available only while the work item is queued.
  *
  * %WORK_OFFQ_CANCELING is used to mark a work item which is being
  * canceled.  While being canceled, a work item may have its PENDING set
  * but stay off timer and worklist for arbitrarily long and nobody should
  * try to steal the PENDING bit.
  */
 static inline void set_work_data(struct work_struct *work, unsigned long data,
                  unsigned long flags)
 {
     WARN_ON_ONCE(!work_pending(work));
     atomic_long_set(&work->data, data | flags | work_static(work));
 }
 
 static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
              unsigned long extra_flags)
 {
     set_work_data(work, (unsigned long)pwq,
               WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | extra_flags);
 }
 
 static void set_work_pool_and_keep_pending(struct work_struct *work,
                        int pool_id)
 {
     set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT,
               WORK_STRUCT_PENDING);
 }
 
 static void set_work_pool_and_clear_pending(struct work_struct *work,
                         int pool_id)
 {
     /*
      * The following wmb is paired with the implied mb in
      * test_and_set_bit(PENDING) and ensures all updates to @work made
      * here are visible to and precede any updates by the next PENDING
      * owner.
      */
     smp_wmb();
     set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
     /*
      * The following mb guarantees that previous clear of a PENDING bit
      * will not be reordered with any speculative LOADS or STORES from
      * work->current_func, which is executed afterwards.  This possible
      * reordering can lead to a missed execution on attempt to queue
      * the same @work.  E.g. consider this case:
      *
      *   CPU#0                         CPU#1
      *   ----------------------------  --------------------------------
      *
      * 1  STORE event_indicated
      * 2  queue_work_on() {
      * 3    test_and_set_bit(PENDING)
      * 4 }                             set_..._and_clear_pending() {
      * 5                                 set_work_data() # clear bit
      * 6                                 smp_mb()
      * 7                               work->current_func() {
      * 8                      LOAD event_indicated
      *                 }
      *
      * Without an explicit full barrier speculative LOAD on line 8 can
      * be executed before CPU#0 does STORE on line 1.  If that happens,
      * CPU#0 observes the PENDING bit is still set and new execution of
      * a @work is not queued in a hope, that CPU#1 will eventually
      * finish the queued @work.  Meanwhile CPU#1 does not see
      * event_indicated is set, because speculative LOAD was executed
      * before actual STORE.
      */
     smp_mb();
 }
 
 static void clear_work_data(struct work_struct *work)
 {
     smp_wmb();  /* see set_work_pool_and_clear_pending() */
     set_work_data(work, WORK_STRUCT_NO_POOL, 0);
 }
 
 static struct pool_workqueue *get_work_pwq(struct work_struct *work)
 {
     unsigned long data = atomic_long_read(&work->data);
 
     if (data & WORK_STRUCT_PWQ)
         return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
     else
         return NULL;
 }
 
 /**
  * get_work_pool - return the worker_pool a given work was associated with
  * @work: the work item of interest
  *
  * Pools are created and destroyed under wq_pool_mutex, and allows read
  * access under RCU read lock.  As such, this function should be
  * called under wq_pool_mutex or inside of a rcu_read_lock() region.
  *
  * All fields of the returned pool are accessible as long as the above
  * mentioned locking is in effect.  If the returned pool needs to be used
  * beyond the critical section, the caller is responsible for ensuring the
  * returned pool is and stays online.
  *
  * Return: The worker_pool @work was last associated with.  %NULL if none.
  */
 static struct worker_pool *get_work_pool(struct work_struct *work)
 {
     unsigned long data = atomic_long_read(&work->data);
     int pool_id;
 
     assert_rcu_or_pool_mutex();
 
     if (data & WORK_STRUCT_PWQ)
         return ((struct pool_workqueue *)
             (data & WORK_STRUCT_WQ_DATA_MASK))->pool;
 
     pool_id = data >> WORK_OFFQ_POOL_SHIFT;
     if (pool_id == WORK_OFFQ_POOL_NONE)
         return NULL;
 
     return idr_find(&worker_pool_idr, pool_id);
 }
 
 /**
  * get_work_pool_id - return the worker pool ID a given work is associated with
  * @work: the work item of interest
  *
  * Return: The worker_pool ID @work was last associated with.
  * %WORK_OFFQ_POOL_NONE if none.
  */
 static int get_work_pool_id(struct work_struct *work)
 {
     unsigned long data = atomic_long_read(&work->data);
 
     if (data & WORK_STRUCT_PWQ)
         return ((struct pool_workqueue *)
             (data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
 
     return data >> WORK_OFFQ_POOL_SHIFT;
 }
 
 static void mark_work_canceling(struct work_struct *work)
 {
     unsigned long pool_id = get_work_pool_id(work);
 
     pool_id <<= WORK_OFFQ_POOL_SHIFT;
     set_work_data(work, pool_id | WORK_OFFQ_CANCELING, WORK_STRUCT_PENDING);
 }
 
 static bool work_is_canceling(struct work_struct *work)
 {
     unsigned long data = atomic_long_read(&work->data);
 
     return !(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_CANCELING);
 }
 
 /*
  * Policy functions.  These define the policies on how the global worker
  * pools are managed.  Unless noted otherwise, these functions assume that
  * they're being called with pool->lock held.
  */
 
 static bool __need_more_worker(struct worker_pool *pool)
 {
     return !pool->nr_running;
 }
 
 /*
  * Need to wake up a worker?  Called from anything but currently
  * running workers.
  *
  * Note that, because unbound workers never contribute to nr_running, this
  * function will always return %true for unbound pools as long as the
  * worklist isn't empty.
  */
 static bool need_more_worker(struct worker_pool *pool)
 {
     return !list_empty(&pool->worklist) && __need_more_worker(pool);
 }
 
 /* Can I start working?  Called from busy but !running workers. */
 static bool may_start_working(struct worker_pool *pool)
 {
     return pool->nr_idle;
 }
 
 /* Do I need to keep working?  Called from currently running workers. */
 static bool keep_working(struct worker_pool *pool)
 {
     return !list_empty(&pool->worklist) && (pool->nr_running <= 1);
 }
 
 /* Do we need a new worker?  Called from manager. */
 static bool need_to_create_worker(struct worker_pool *pool)
 {
     return need_more_worker(pool) && !may_start_working(pool);
 }
 
 /* Do we have too many workers and should some go away? */
 static bool too_many_workers(struct worker_pool *pool)
 {
     bool managing = pool->flags & POOL_MANAGER_ACTIVE;
     int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
     int nr_busy = pool->nr_workers - nr_idle;
 
     return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
 }
 
 /*
  * Wake up functions.
  */
 
 /* Return the first idle worker.  Called with pool->lock held. */
 static struct worker *first_idle_worker(struct worker_pool *pool)
 {
     if (unlikely(list_empty(&pool->idle_list)))
         return NULL;
 
     return list_first_entry(&pool->idle_list, struct worker, entry);
 }
 
 /**
  * wake_up_worker - wake up an idle worker
  * @pool: worker pool to wake worker from
  *
  * Wake up the first idle worker of @pool.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void wake_up_worker(struct worker_pool *pool)
 {
     struct worker *worker = first_idle_worker(pool);
 
     if (likely(worker))
         wake_up_process(worker->task);
 }
 
 /**
  * wq_worker_running - a worker is running again
  * @task: task waking up
  *
  * This function is called when a worker returns from schedule()
  */
 void wq_worker_running(struct task_struct *task)
 {
     struct worker *worker = kthread_data(task);
 
     if (!worker->sleeping)
         return;
 
     /*
      * If preempted by unbind_workers() between the WORKER_NOT_RUNNING check
      * and the nr_running increment below, we may ruin the nr_running reset
      * and leave with an unexpected pool->nr_running == 1 on the newly unbound
      * pool. Protect against such race.
      */
     preempt_disable();
     if (!(worker->flags & WORKER_NOT_RUNNING))
         worker->pool->nr_running++;
     preempt_enable();
     worker->sleeping = 0;
 }
 
 /**
  * wq_worker_sleeping - a worker is going to sleep
  * @task: task going to sleep
  *
  * This function is called from schedule() when a busy worker is
  * going to sleep.
  */
 void wq_worker_sleeping(struct task_struct *task)
 {
     struct worker *worker = kthread_data(task);
     struct worker_pool *pool;
 
     /*
      * Rescuers, which may not have all the fields set up like normal
      * workers, also reach here, let's not access anything before
      * checking NOT_RUNNING.
      */
     if (worker->flags & WORKER_NOT_RUNNING)
         return;
 
     pool = worker->pool;
 
     /* Return if preempted before wq_worker_running() was reached */
     if (worker->sleeping)
         return;
 
     worker->sleeping = 1;
     raw_spin_lock_irq(&pool->lock);
 
     /*
      * Recheck in case unbind_workers() preempted us. We don't
      * want to decrement nr_running after the worker is unbound
      * and nr_running has been reset.
      */
     if (worker->flags & WORKER_NOT_RUNNING) {
         raw_spin_unlock_irq(&pool->lock);
         return;
     }
 
     pool->nr_running--;
     if (need_more_worker(pool))
         wake_up_worker(pool);
     raw_spin_unlock_irq(&pool->lock);
 }
 
 /**
  * wq_worker_last_func - retrieve worker's last work function
  * @task: Task to retrieve last work function of.
  *
  * Determine the last function a worker executed. This is called from
  * the scheduler to get a worker's last known identity.
  *
  * CONTEXT:
  * raw_spin_lock_irq(rq->lock)
  *
  * This function is called during schedule() when a kworker is going
  * to sleep. It's used by psi to identify aggregation workers during
  * dequeuing, to allow periodic aggregation to shut-off when that
  * worker is the last task in the system or cgroup to go to sleep.
  *
  * As this function doesn't involve any workqueue-related locking, it
  * only returns stable values when called from inside the scheduler's
  * queuing and dequeuing paths, when @task, which must be a kworker,
  * is guaranteed to not be processing any works.
  *
  * Return:
  * The last work function %current executed as a worker, NULL if it
  * hasn't executed any work yet.
  */
 work_func_t wq_worker_last_func(struct task_struct *task)
 {
     struct worker *worker = kthread_data(task);
 
     return worker->last_func;
 }
 
 /**
  * worker_set_flags - set worker flags and adjust nr_running accordingly
  * @worker: self
  * @flags: flags to set
  *
  * Set @flags in @worker->flags and adjust nr_running accordingly.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock)
  */
 static inline void worker_set_flags(struct worker *worker, unsigned int flags)
 {
     struct worker_pool *pool = worker->pool;
 
     WARN_ON_ONCE(worker->task != current);
 
     /* If transitioning into NOT_RUNNING, adjust nr_running. */
     if ((flags & WORKER_NOT_RUNNING) &&
         !(worker->flags & WORKER_NOT_RUNNING)) {
         pool->nr_running--;
     }
 
     worker->flags |= flags;
 }
 
 /**
  * worker_clr_flags - clear worker flags and adjust nr_running accordingly
  * @worker: self
  * @flags: flags to clear
  *
  * Clear @flags in @worker->flags and adjust nr_running accordingly.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock)
  */
 static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
 {
     struct worker_pool *pool = worker->pool;
     unsigned int oflags = worker->flags;
 
     WARN_ON_ONCE(worker->task != current);
 
     worker->flags &= ~flags;
 
     /*
      * If transitioning out of NOT_RUNNING, increment nr_running.  Note
      * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
      * of multiple flags, not a single flag.
      */
     if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
         if (!(worker->flags & WORKER_NOT_RUNNING))
             pool->nr_running++;
 }
 
 /**
  * find_worker_executing_work - find worker which is executing a work
  * @pool: pool of interest
  * @work: work to find worker for
  *
  * Find a worker which is executing @work on @pool by searching
  * @pool->busy_hash which is keyed by the address of @work.  For a worker
  * to match, its current execution should match the address of @work and
  * its work function.  This is to avoid unwanted dependency between
  * unrelated work executions through a work item being recycled while still
  * being executed.
  *
  * This is a bit tricky.  A work item may be freed once its execution
  * starts and nothing prevents the freed area from being recycled for
  * another work item.  If the same work item address ends up being reused
  * before the original execution finishes, workqueue will identify the
  * recycled work item as currently executing and make it wait until the
  * current execution finishes, introducing an unwanted dependency.
  *
  * This function checks the work item address and work function to avoid
  * false positives.  Note that this isn't complete as one may construct a
  * work function which can introduce dependency onto itself through a
  * recycled work item.  Well, if somebody wants to shoot oneself in the
  * foot that badly, there's only so much we can do, and if such deadlock
  * actually occurs, it should be easy to locate the culprit work function.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  *
  * Return:
  * Pointer to worker which is executing @work if found, %NULL
  * otherwise.
  */
 static struct worker *find_worker_executing_work(struct worker_pool *pool,
                          struct work_struct *work)
 {
     struct worker *worker;
 
     hash_for_each_possible(pool->busy_hash, worker, hentry,
                    (unsigned long)work)
         if (worker->current_work == work &&
             worker->current_func == work->func)
             return worker;
 
     return NULL;
 }
 
 /**
  * move_linked_works - move linked works to a list
  * @work: start of series of works to be scheduled
  * @head: target list to append @work to
  * @nextp: out parameter for nested worklist walking
  *
  * Schedule linked works starting from @work to @head.  Work series to
  * be scheduled starts at @work and includes any consecutive work with
  * WORK_STRUCT_LINKED set in its predecessor.
  *
  * If @nextp is not NULL, it's updated to point to the next work of
  * the last scheduled work.  This allows move_linked_works() to be
  * nested inside outer list_for_each_entry_safe().
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void move_linked_works(struct work_struct *work, struct list_head *head,
                   struct work_struct **nextp)
 {
     struct work_struct *n;
 
     /*
      * Linked worklist will always end before the end of the list,
      * use NULL for list head.
      */
     list_for_each_entry_safe_from(work, n, NULL, entry) {
         list_move_tail(&work->entry, head);
         if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
             break;
     }
 
     /*
      * If we're already inside safe list traversal and have moved
      * multiple works to the scheduled queue, the next position
      * needs to be updated.
      */
     if (nextp)
         *nextp = n;
 }
 
 /**
  * get_pwq - get an extra reference on the specified pool_workqueue
  * @pwq: pool_workqueue to get
  *
  * Obtain an extra reference on @pwq.  The caller should guarantee that
  * @pwq has positive refcnt and be holding the matching pool->lock.
  */
 static void get_pwq(struct pool_workqueue *pwq)
 {
     lockdep_assert_held(&pwq->pool->lock);
     WARN_ON_ONCE(pwq->refcnt <= 0);
     pwq->refcnt++;
 }
 
 /**
  * put_pwq - put a pool_workqueue reference
  * @pwq: pool_workqueue to put
  *
  * Drop a reference of @pwq.  If its refcnt reaches zero, schedule its
  * destruction.  The caller should be holding the matching pool->lock.
  */
 static void put_pwq(struct pool_workqueue *pwq)
 {
     lockdep_assert_held(&pwq->pool->lock);
     if (likely(--pwq->refcnt))
         return;
     if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
         return;
     /*
      * @pwq can't be released under pool->lock, bounce to
      * pwq_unbound_release_workfn().  This never recurses on the same
      * pool->lock as this path is taken only for unbound workqueues and
      * the release work item is scheduled on a per-cpu workqueue.  To
      * avoid lockdep warning, unbound pool->locks are given lockdep
      * subclass of 1 in get_unbound_pool().
      */
     schedule_work(&pwq->unbound_release_work);
 }
 
 /**
  * put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
  * @pwq: pool_workqueue to put (can be %NULL)
  *
  * put_pwq() with locking.  This function also allows %NULL @pwq.
  */
 static void put_pwq_unlocked(struct pool_workqueue *pwq)
 {
     if (pwq) {
         /*
          * As both pwqs and pools are RCU protected, the
          * following lock operations are safe.
          */
         raw_spin_lock_irq(&pwq->pool->lock);
         put_pwq(pwq);
         raw_spin_unlock_irq(&pwq->pool->lock);
     }
 }
 
 static void pwq_activate_inactive_work(struct work_struct *work)
 {
     struct pool_workqueue *pwq = get_work_pwq(work);
 
     trace_workqueue_activate_work(work);
     if (list_empty(&pwq->pool->worklist))
         pwq->pool->watchdog_ts = jiffies;
     move_linked_works(work, &pwq->pool->worklist, NULL);
     __clear_bit(WORK_STRUCT_INACTIVE_BIT, work_data_bits(work));
     pwq->nr_active++;
 }
 
 static void pwq_activate_first_inactive(struct pool_workqueue *pwq)
 {
     struct work_struct *work = list_first_entry(&pwq->inactive_works,
                             struct work_struct, entry);
 
     pwq_activate_inactive_work(work);
 }
 
 /**
  * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
  * @pwq: pwq of interest
  * @work_data: work_data of work which left the queue
  *
  * A work either has completed or is removed from pending queue,
  * decrement nr_in_flight of its pwq and handle workqueue flushing.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_data)
 {
     int color = get_work_color(work_data);
 
     if (!(work_data & WORK_STRUCT_INACTIVE)) {
         pwq->nr_active--;
         if (!list_empty(&pwq->inactive_works)) {
             /* one down, submit an inactive one */
             if (pwq->nr_active < pwq->max_active)
                 pwq_activate_first_inactive(pwq);
         }
     }
 
     pwq->nr_in_flight[color]--;
 
     /* is flush in progress and are we at the flushing tip? */
     if (likely(pwq->flush_color != color))
         goto out_put;
 
     /* are there still in-flight works? */
     if (pwq->nr_in_flight[color])
         goto out_put;
 
     /* this pwq is done, clear flush_color */
     pwq->flush_color = -1;
 
     /*
      * If this was the last pwq, wake up the first flusher.  It
      * will handle the rest.
      */
     if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
         complete(&pwq->wq->first_flusher->done);
 out_put:
     put_pwq(pwq);
 }
 
 /**
  * try_to_grab_pending - steal work item from worklist and disable irq
  * @work: work item to steal
  * @is_dwork: @work is a delayed_work
  * @flags: place to store irq state
  *
  * Try to grab PENDING bit of @work.  This function can handle @work in any
  * stable state - idle, on timer or on worklist.
  *
  * Return:
  *
  *  ========    ================================================================
  *  1       if @work was pending and we successfully stole PENDING
  *  0       if @work was idle and we claimed PENDING
  *  -EAGAIN if PENDING couldn't be grabbed at the moment, safe to busy-retry
  *  -ENOENT if someone else is canceling @work, this state may persist
  *      for arbitrarily long
  *  ========    ================================================================
  *
  * Note:
  * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting
  * interrupted while holding PENDING and @work off queue, irq must be
  * disabled on entry.  This, combined with delayed_work->timer being
  * irqsafe, ensures that we return -EAGAIN for finite short period of time.
  *
  * On successful return, >= 0, irq is disabled and the caller is
  * responsible for releasing it using local_irq_restore(*@flags).
  *
  * This function is safe to call from any context including IRQ handler.
  */
 static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
                    unsigned long *flags)
 {
     struct worker_pool *pool;
     struct pool_workqueue *pwq;
 
     local_irq_save(*flags);
 
     /* try to steal the timer if it exists */
     if (is_dwork) {
         struct delayed_work *dwork = to_delayed_work(work);
 
         /*
          * dwork->timer is irqsafe.  If del_timer() fails, it's
          * guaranteed that the timer is not queued anywhere and not
          * running on the local CPU.
          */
         if (likely(del_timer(&dwork->timer)))
             return 1;
     }
 
     /* try to claim PENDING the normal way */
     if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
         return 0;
 
     rcu_read_lock();
     /*
      * The queueing is in progress, or it is already queued. Try to
      * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
      */
     pool = get_work_pool(work);
     if (!pool)
         goto fail;
 
     raw_spin_lock(&pool->lock);
     /*
      * work->data is guaranteed to point to pwq only while the work
      * item is queued on pwq->wq, and both updating work->data to point
      * to pwq on queueing and to pool on dequeueing are done under
      * pwq->pool->lock.  This in turn guarantees that, if work->data
      * points to pwq which is associated with a locked pool, the work
      * item is currently queued on that pool.
      */
     pwq = get_work_pwq(work);
     if (pwq && pwq->pool == pool) {
         debug_work_deactivate(work);
 
         /*
          * A cancelable inactive work item must be in the
          * pwq->inactive_works since a queued barrier can't be
          * canceled (see the comments in insert_wq_barrier()).
          *
          * An inactive work item cannot be grabbed directly because
          * it might have linked barrier work items which, if left
          * on the inactive_works list, will confuse pwq->nr_active
          * management later on and cause stall.  Make sure the work
          * item is activated before grabbing.
          */
         if (*work_data_bits(work) & WORK_STRUCT_INACTIVE)
             pwq_activate_inactive_work(work);
 
         list_del_init(&work->entry);
         pwq_dec_nr_in_flight(pwq, *work_data_bits(work));
 
         /* work->data points to pwq iff queued, point to pool */
         set_work_pool_and_keep_pending(work, pool->id);
 
         raw_spin_unlock(&pool->lock);
         rcu_read_unlock();
         return 1;
     }
     raw_spin_unlock(&pool->lock);
 fail:
     rcu_read_unlock();
     local_irq_restore(*flags);
     if (work_is_canceling(work))
         return -ENOENT;
     cpu_relax();
     return -EAGAIN;
 }
 
 /**
  * insert_work - insert a work into a pool
  * @pwq: pwq @work belongs to
  * @work: work to insert
  * @head: insertion point
  * @extra_flags: extra WORK_STRUCT_* flags to set
  *
  * Insert @work which belongs to @pwq after @head.  @extra_flags is or'd to
  * work_struct flags.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
             struct list_head *head, unsigned int extra_flags)
 {
     struct worker_pool *pool = pwq->pool;
 
     /* record the work call stack in order to print it in KASAN reports */
     kasan_record_aux_stack_noalloc(work);
 
     /* we own @work, set data and link */
     set_work_pwq(work, pwq, extra_flags);
     list_add_tail(&work->entry, head);
     get_pwq(pwq);
 
     if (__need_more_worker(pool))
         wake_up_worker(pool);
 }
 
 /*
  * Test whether @work is being queued from another work executing on the
  * same workqueue.
  */
 static bool is_chained_work(struct workqueue_struct *wq)
 {
     struct worker *worker;
 
     worker = current_wq_worker();
     /*
      * Return %true iff I'm a worker executing a work item on @wq.  If
      * I'm @worker, it's safe to dereference it without locking.
      */
     return worker && worker->current_pwq->wq == wq;
 }
 
 /*
  * When queueing an unbound work item to a wq, prefer local CPU if allowed
  * by wq_unbound_cpumask.  Otherwise, round robin among the allowed ones to
  * avoid perturbing sensitive tasks.
  */
 static int wq_select_unbound_cpu(int cpu)
 {
     static bool printed_dbg_warning;
     int new_cpu;
 
     if (likely(!wq_debug_force_rr_cpu)) {
         if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
             return cpu;
     } else if (!printed_dbg_warning) {
         pr_warn("workqueue: round-robin CPU selection forced, expect performance impact\n");
         printed_dbg_warning = true;
     }
 
     if (cpumask_empty(wq_unbound_cpumask))
         return cpu;
 
     new_cpu = __this_cpu_read(wq_rr_cpu_last);
     new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
     if (unlikely(new_cpu >= nr_cpu_ids)) {
         new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
         if (unlikely(new_cpu >= nr_cpu_ids))
             return cpu;
     }
     __this_cpu_write(wq_rr_cpu_last, new_cpu);
 
     return new_cpu;
 }
 
 static void __queue_work(int cpu, struct workqueue_struct *wq,
              struct work_struct *work)
 {
     struct pool_workqueue *pwq;
     struct worker_pool *last_pool;
     struct list_head *worklist;
     unsigned int work_flags;
     unsigned int req_cpu = cpu;
 
     /*
      * While a work item is PENDING && off queue, a task trying to
      * steal the PENDING will busy-loop waiting for it to either get
      * queued or lose PENDING.  Grabbing PENDING and queueing should
      * happen with IRQ disabled.
      */
     lockdep_assert_irqs_disabled();
 
 
     /* if draining, only works from the same workqueue are allowed */
     if (unlikely(wq->flags & __WQ_DRAINING) &&
         WARN_ON_ONCE(!is_chained_work(wq)))
         return;
     rcu_read_lock();
 retry:
     /* pwq which will be used unless @work is executing elsewhere */
     if (wq->flags & WQ_UNBOUND) {
         if (req_cpu == WORK_CPU_UNBOUND)
             cpu = wq_select_unbound_cpu(raw_smp_processor_id());
         pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
     } else {
         if (req_cpu == WORK_CPU_UNBOUND)
             cpu = raw_smp_processor_id();
         pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
     }
 
     /*
      * If @work was previously on a different pool, it might still be
      * running there, in which case the work needs to be queued on that
      * pool to guarantee non-reentrancy.
      */
     last_pool = get_work_pool(work);
     if (last_pool && last_pool != pwq->pool) {
         struct worker *worker;
 
         raw_spin_lock(&last_pool->lock);
 
         worker = find_worker_executing_work(last_pool, work);
 
         if (worker && worker->current_pwq->wq == wq) {
             pwq = worker->current_pwq;
         } else {
             /* meh... not running there, queue here */
             raw_spin_unlock(&last_pool->lock);
             raw_spin_lock(&pwq->pool->lock);
         }
     } else {
         raw_spin_lock(&pwq->pool->lock);
     }
 
     /*
      * pwq is determined and locked.  For unbound pools, we could have
      * raced with pwq release and it could already be dead.  If its
      * refcnt is zero, repeat pwq selection.  Note that pwqs never die
      * without another pwq replacing it in the numa_pwq_tbl or while
      * work items are executing on it, so the retrying is guaranteed to
      * make forward-progress.
      */
     if (unlikely(!pwq->refcnt)) {
         if (wq->flags & WQ_UNBOUND) {
             raw_spin_unlock(&pwq->pool->lock);
             cpu_relax();
             goto retry;
         }
         /* oops */
         WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
               wq->name, cpu);
     }
 
     /* pwq determined, queue */
     trace_workqueue_queue_work(req_cpu, pwq, work);
 
     if (WARN_ON(!list_empty(&work->entry)))
         goto out;
 
     pwq->nr_in_flight[pwq->work_color]++;
     work_flags = work_color_to_flags(pwq->work_color);
 
     if (likely(pwq->nr_active < pwq->max_active)) {
         trace_workqueue_activate_work(work);
         pwq->nr_active++;
         worklist = &pwq->pool->worklist;
         if (list_empty(worklist))
             pwq->pool->watchdog_ts = jiffies;
     } else {
         work_flags |= WORK_STRUCT_INACTIVE;
         worklist = &pwq->inactive_works;
     }
 
     debug_work_activate(work);
     insert_work(pwq, work, worklist, work_flags);
 
 out:
     raw_spin_unlock(&pwq->pool->lock);
     rcu_read_unlock();
 }
 
 /**
  * queue_work_on - queue work on specific cpu
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @work: work to queue
  *
  * We queue the work to a specific CPU, the caller must ensure it
  * can't go away.  Callers that fail to ensure that the specified
  * CPU cannot go away will execute on a randomly chosen CPU.
  *
  * Return: %false if @work was already on a queue, %true otherwise.
  */
 bool queue_work_on(int cpu, struct workqueue_struct *wq,
            struct work_struct *work)
 {
     bool ret = false;
     unsigned long flags;
 
     local_irq_save(flags);
 
     if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
         __queue_work(cpu, wq, work);
         ret = true;
     }
 
     local_irq_restore(flags);
     return ret;
 }
 EXPORT_SYMBOL(queue_work_on);
 
 /**
  * workqueue_select_cpu_near - Select a CPU based on NUMA node
  * @node: NUMA node ID that we want to select a CPU from
  *
  * This function will attempt to find a "random" cpu available on a given
  * node. If there are no CPUs available on the given node it will return
  * WORK_CPU_UNBOUND indicating that we should just schedule to any
  * available CPU if we need to schedule this work.
  */
 static int workqueue_select_cpu_near(int node)
 {
     int cpu;
 
     /* No point in doing this if NUMA isn't enabled for workqueues */
     if (!wq_numa_enabled)
         return WORK_CPU_UNBOUND;
 
     /* Delay binding to CPU if node is not valid or online */
     if (node < 0 || node >= MAX_NUMNODES || !node_online(node))
         return WORK_CPU_UNBOUND;
 
     /* Use local node/cpu if we are already there */
     cpu = raw_smp_processor_id();
     if (node == cpu_to_node(cpu))
         return cpu;
 
     /* Use "random" otherwise know as "first" online CPU of node */
     cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
 
     /* If CPU is valid return that, otherwise just defer */
     return cpu < nr_cpu_ids ? cpu : WORK_CPU_UNBOUND;
 }
 
 /**
  * queue_work_node - queue work on a "random" cpu for a given NUMA node
  * @node: NUMA node that we are targeting the work for
  * @wq: workqueue to use
  * @work: work to queue
  *
  * We queue the work to a "random" CPU within a given NUMA node. The basic
  * idea here is to provide a way to somehow associate work with a given
  * NUMA node.
  *
  * This function will only make a best effort attempt at getting this onto
  * the right NUMA node. If no node is requested or the requested node is
  * offline then we just fall back to standard queue_work behavior.
  *
  * Currently the "random" CPU ends up being the first available CPU in the
  * intersection of cpu_online_mask and the cpumask of the node, unless we
  * are running on the node. In that case we just use the current CPU.
  *
  * Return: %false if @work was already on a queue, %true otherwise.
  */
 bool queue_work_node(int node, struct workqueue_struct *wq,
              struct work_struct *work)
 {
     unsigned long flags;
     bool ret = false;
 
     /*
      * This current implementation is specific to unbound workqueues.
      * Specifically we only return the first available CPU for a given
      * node instead of cycling through individual CPUs within the node.
      *
      * If this is used with a per-cpu workqueue then the logic in
      * workqueue_select_cpu_near would need to be updated to allow for
      * some round robin type logic.
      */
     WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND));
 
     local_irq_save(flags);
 
     if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
         int cpu = workqueue_select_cpu_near(node);
 
         __queue_work(cpu, wq, work);
         ret = true;
     }
 
     local_irq_restore(flags);
     return ret;
 }
 EXPORT_SYMBOL_GPL(queue_work_node);
 
 void delayed_work_timer_fn(struct timer_list *t)
 {
     struct delayed_work *dwork = from_timer(dwork, t, timer);
 
     /* should have been called from irqsafe timer with irq already off */
     __queue_work(dwork->cpu, dwork->wq, &dwork->work);
 }
 EXPORT_SYMBOL(delayed_work_timer_fn);
 
 static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
                 struct delayed_work *dwork, unsigned long delay)
 {
     struct timer_list *timer = &dwork->timer;
     struct work_struct *work = &dwork->work;
 
     WARN_ON_ONCE(!wq);
     WARN_ON_FUNCTION_MISMATCH(timer->function, delayed_work_timer_fn);
     WARN_ON_ONCE(timer_pending(timer));
     WARN_ON_ONCE(!list_empty(&work->entry));
 
     /*
      * If @delay is 0, queue @dwork->work immediately.  This is for
      * both optimization and correctness.  The earliest @timer can
      * expire is on the closest next tick and delayed_work users depend
      * on that there's no such delay when @delay is 0.
      */
     if (!delay) {
         __queue_work(cpu, wq, &dwork->work);
         return;
     }
 
     dwork->wq = wq;
     dwork->cpu = cpu;
     timer->expires = jiffies + delay;
 
     if (unlikely(cpu != WORK_CPU_UNBOUND))
         add_timer_on(timer, cpu);
     else
         add_timer(timer);
 }
 
 /**
  * queue_delayed_work_on - queue work on specific CPU after delay
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @dwork: work to queue
  * @delay: number of jiffies to wait before queueing
  *
  * Return: %false if @work was already on a queue, %true otherwise.  If
  * @delay is zero and @dwork is idle, it will be scheduled for immediate
  * execution.
  */
 bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
                struct delayed_work *dwork, unsigned long delay)
 {
     struct work_struct *work = &dwork->work;
     bool ret = false;
     unsigned long flags;
 
     /* read the comment in __queue_work() */
     local_irq_save(flags);
 
     if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
         __queue_delayed_work(cpu, wq, dwork, delay);
         ret = true;
     }
 
     local_irq_restore(flags);
     return ret;
 }
 EXPORT_SYMBOL(queue_delayed_work_on);
 
 /**
  * mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @dwork: work to queue
  * @delay: number of jiffies to wait before queueing
  *
  * If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
  * modify @dwork's timer so that it expires after @delay.  If @delay is
  * zero, @work is guaranteed to be scheduled immediately regardless of its
  * current state.
  *
  * Return: %false if @dwork was idle and queued, %true if @dwork was
  * pending and its timer was modified.
  *
  * This function is safe to call from any context including IRQ handler.
  * See try_to_grab_pending() for details.
  */
 bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
              struct delayed_work *dwork, unsigned long delay)
 {
     unsigned long flags;
     int ret;
 
     do {
         ret = try_to_grab_pending(&dwork->work, true, &flags);
     } while (unlikely(ret == -EAGAIN));
 
     if (likely(ret >= 0)) {
         __queue_delayed_work(cpu, wq, dwork, delay);
         local_irq_restore(flags);
     }
 
     /* -ENOENT from try_to_grab_pending() becomes %true */
     return ret;
 }
 EXPORT_SYMBOL_GPL(mod_delayed_work_on);
 
 static void rcu_work_rcufn(struct rcu_head *rcu)
 {
     struct rcu_work *rwork = container_of(rcu, struct rcu_work, rcu);
 
     /* read the comment in __queue_work() */
     local_irq_disable();
     __queue_work(WORK_CPU_UNBOUND, rwork->wq, &rwork->work);
     local_irq_enable();
 }
 
 /**
  * queue_rcu_work - queue work after a RCU grace period
  * @wq: workqueue to use
  * @rwork: work to queue
  *
  * Return: %false if @rwork was already pending, %true otherwise.  Note
  * that a full RCU grace period is guaranteed only after a %true return.
  * While @rwork is guaranteed to be executed after a %false return, the
  * execution may happen before a full RCU grace period has passed.
  */
 bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
 {
     struct work_struct *work = &rwork->work;
 
     if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
         rwork->wq = wq;
         call_rcu(&rwork->rcu, rcu_work_rcufn);
         return true;
     }
 
     return false;
 }
 EXPORT_SYMBOL(queue_rcu_work);
 
 /**
  * worker_enter_idle - enter idle state
  * @worker: worker which is entering idle state
  *
  * @worker is entering idle state.  Update stats and idle timer if
  * necessary.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock).
  */
 static void worker_enter_idle(struct worker *worker)
 {
     struct worker_pool *pool = worker->pool;
 
     if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
         WARN_ON_ONCE(!list_empty(&worker->entry) &&
              (worker->hentry.next || worker->hentry.pprev)))
         return;
 
     /* can't use worker_set_flags(), also called from create_worker() */
     worker->flags |= WORKER_IDLE;
     pool->nr_idle++;
     worker->last_active = jiffies;
 
     /* idle_list is LIFO */
     list_add(&worker->entry, &pool->idle_list);
 
     if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
         mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
 
     /* Sanity check nr_running. */
     WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
 }
 
 /**
  * worker_leave_idle - leave idle state
  * @worker: worker which is leaving idle state
  *
  * @worker is leaving idle state.  Update stats.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock).
  */
 static void worker_leave_idle(struct worker *worker)
 {
     struct worker_pool *pool = worker->pool;
 
     if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
         return;
     worker_clr_flags(worker, WORKER_IDLE);
     pool->nr_idle--;
     list_del_init(&worker->entry);
 }
 
 static struct worker *alloc_worker(int node)
 {
     struct worker *worker;
 
     worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node);
     if (worker) {
         INIT_LIST_HEAD(&worker->entry);
         INIT_LIST_HEAD(&worker->scheduled);
         INIT_LIST_HEAD(&worker->node);
         /* on creation a worker is in !idle && prep state */
         worker->flags = WORKER_PREP;
     }
     return worker;
 }
 
 /**
  * worker_attach_to_pool() - attach a worker to a pool
  * @worker: worker to be attached
  * @pool: the target pool
  *
  * Attach @worker to @pool.  Once attached, the %WORKER_UNBOUND flag and
  * cpu-binding of @worker are kept coordinated with the pool across
  * cpu-[un]hotplugs.
  */
 static void worker_attach_to_pool(struct worker *worker,
                    struct worker_pool *pool)
 {
     mutex_lock(&wq_pool_attach_mutex);
 
     /*
      * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
      * stable across this function.  See the comments above the flag
      * definition for details.
      */
     if (pool->flags & POOL_DISASSOCIATED)
         worker->flags |= WORKER_UNBOUND;
     else
         kthread_set_per_cpu(worker->task, pool->cpu);
 
     if (worker->rescue_wq)
         set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
 
     list_add_tail(&worker->node, &pool->workers);
     worker->pool = pool;
 
     mutex_unlock(&wq_pool_attach_mutex);
 }
 
 /**
  * worker_detach_from_pool() - detach a worker from its pool
  * @worker: worker which is attached to its pool
  *
  * Undo the attaching which had been done in worker_attach_to_pool().  The
  * caller worker shouldn't access to the pool after detached except it has
  * other reference to the pool.
  */
 static void worker_detach_from_pool(struct worker *worker)
 {
     struct worker_pool *pool = worker->pool;
     struct completion *detach_completion = NULL;
 
     mutex_lock(&wq_pool_attach_mutex);
 
     kthread_set_per_cpu(worker->task, -1);
     list_del(&worker->node);
     worker->pool = NULL;
 
     if (list_empty(&pool->workers))
         detach_completion = pool->detach_completion;
     mutex_unlock(&wq_pool_attach_mutex);
 
     /* clear leftover flags without pool->lock after it is detached */
     worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);
 
     if (detach_completion)
         complete(detach_completion);
 }
 
 /**
  * create_worker - create a new workqueue worker
  * @pool: pool the new worker will belong to
  *
  * Create and start a new worker which is attached to @pool.
  *
  * CONTEXT:
  * Might sleep.  Does GFP_KERNEL allocations.
  *
  * Return:
  * Pointer to the newly created worker.
  */
 static struct worker *create_worker(struct worker_pool *pool)
 {
     struct worker *worker;
     int id;
     char id_buf[16];
 
     /* ID is needed to determine kthread name */
     id = ida_alloc(&pool->worker_ida, GFP_KERNEL);
     if (id < 0)
         return NULL;
 
     worker = alloc_worker(pool->node);
     if (!worker)
         goto fail;
 
     worker->id = id;
 
     if (pool->cpu >= 0)
         snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
              pool->attrs->nice < 0  ? "H" : "");
     else
         snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
 
     worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
                           "kworker/%s", id_buf);
     if (IS_ERR(worker->task))
         goto fail;
 
     set_user_nice(worker->task, pool->attrs->nice);
     kthread_bind_mask(worker->task, pool->attrs->cpumask);
 
     /* successful, attach the worker to the pool */
     worker_attach_to_pool(worker, pool);
 
     /* start the newly created worker */
     raw_spin_lock_irq(&pool->lock);
     worker->pool->nr_workers++;
     worker_enter_idle(worker);
     wake_up_process(worker->task);
     raw_spin_unlock_irq(&pool->lock);
 
     return worker;
 
 fail:
     ida_free(&pool->worker_ida, id);
     kfree(worker);
     return NULL;
 }
 
 /**
  * destroy_worker - destroy a workqueue worker
  * @worker: worker to be destroyed
  *
  * Destroy @worker and adjust @pool stats accordingly.  The worker should
  * be idle.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void destroy_worker(struct worker *worker)
 {
     struct worker_pool *pool = worker->pool;
 
     lockdep_assert_held(&pool->lock);
 
     /* sanity check frenzy */
     if (WARN_ON(worker->current_work) ||
         WARN_ON(!list_empty(&worker->scheduled)) ||
         WARN_ON(!(worker->flags & WORKER_IDLE)))
         return;
 
     pool->nr_workers--;
     pool->nr_idle--;
 
     list_del_init(&worker->entry);
     worker->flags |= WORKER_DIE;
     wake_up_process(worker->task);
 }
 
 static void idle_worker_timeout(struct timer_list *t)
 {
     struct worker_pool *pool = from_timer(pool, t, idle_timer);
 
     raw_spin_lock_irq(&pool->lock);
 
     while (too_many_workers(pool)) {
         struct worker *worker;
         unsigned long expires;
 
         /* idle_list is kept in LIFO order, check the last one */
         worker = list_entry(pool->idle_list.prev, struct worker, entry);
         expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 
         if (time_before(jiffies, expires)) {
             mod_timer(&pool->idle_timer, expires);
             break;
         }
 
         destroy_worker(worker);
     }
 
     raw_spin_unlock_irq(&pool->lock);
 }
 
 static void send_mayday(struct work_struct *work)
 {
     struct pool_workqueue *pwq = get_work_pwq(work);
     struct workqueue_struct *wq = pwq->wq;
 
     lockdep_assert_held(&wq_mayday_lock);
 
     if (!wq->rescuer)
         return;
 
     /* mayday mayday mayday */
     if (list_empty(&pwq->mayday_node)) {
         /*
          * If @pwq is for an unbound wq, its base ref may be put at
          * any time due to an attribute change.  Pin @pwq until the
          * rescuer is done with it.
          */
         get_pwq(pwq);
         list_add_tail(&pwq->mayday_node, &wq->maydays);
         wake_up_process(wq->rescuer->task);
     }
 }
 
 static void pool_mayday_timeout(struct timer_list *t)
 {
     struct worker_pool *pool = from_timer(pool, t, mayday_timer);
     struct work_struct *work;
 
     raw_spin_lock_irq(&pool->lock);
     raw_spin_lock(&wq_mayday_lock);     /* for wq->maydays */
 
     if (need_to_create_worker(pool)) {
         /*
          * We've been trying to create a new worker but
          * haven't been successful.  We might be hitting an
          * allocation deadlock.  Send distress signals to
          * rescuers.
          */
         list_for_each_entry(work, &pool->worklist, entry)
             send_mayday(work);
     }
 
     raw_spin_unlock(&wq_mayday_lock);
     raw_spin_unlock_irq(&pool->lock);
 
     mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
 }
 
 /**
  * maybe_create_worker - create a new worker if necessary
  * @pool: pool to create a new worker for
  *
  * Create a new worker for @pool if necessary.  @pool is guaranteed to
  * have at least one idle worker on return from this function.  If
  * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
  * sent to all rescuers with works scheduled on @pool to resolve
  * possible allocation deadlock.
  *
  * On return, need_to_create_worker() is guaranteed to be %false and
  * may_start_working() %true.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Does GFP_KERNEL allocations.  Called only from
  * manager.
  */
 static void maybe_create_worker(struct worker_pool *pool)
 __releases(&pool->lock)
 __acquires(&pool->lock)
 {
 restart:
     raw_spin_unlock_irq(&pool->lock);
 
     /* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
     mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
 
     while (true) {
         if (create_worker(pool) || !need_to_create_worker(pool))
             break;
 
         schedule_timeout_interruptible(CREATE_COOLDOWN);
 
         if (!need_to_create_worker(pool))
             break;
     }
 
     del_timer_sync(&pool->mayday_timer);
     raw_spin_lock_irq(&pool->lock);
     /*
      * This is necessary even after a new worker was just successfully
      * created as @pool->lock was dropped and the new worker might have
      * already become busy.
      */
     if (need_to_create_worker(pool))
         goto restart;
 }
 
 /**
  * manage_workers - manage worker pool
  * @worker: self
  *
  * Assume the manager role and manage the worker pool @worker belongs
  * to.  At any given time, there can be only zero or one manager per
  * pool.  The exclusion is handled automatically by this function.
  *
  * The caller can safely start processing works on false return.  On
  * true return, it's guaranteed that need_to_create_worker() is false
  * and may_start_working() is true.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Does GFP_KERNEL allocations.
  *
  * Return:
  * %false if the pool doesn't need management and the caller can safely
  * start processing works, %true if management function was performed and
  * the conditions that the caller verified before calling the function may
  * no longer be true.
  */
 static bool manage_workers(struct worker *worker)
 {
     struct worker_pool *pool = worker->pool;
 
     if (pool->flags & POOL_MANAGER_ACTIVE)
         return false;
 
     pool->flags |= POOL_MANAGER_ACTIVE;
     pool->manager = worker;
 
     maybe_create_worker(pool);
 
     pool->manager = NULL;
     pool->flags &= ~POOL_MANAGER_ACTIVE;
     rcuwait_wake_up(&manager_wait);
     return true;
 }
 
 /**
  * process_one_work - process single work
  * @worker: self
  * @work: work to process
  *
  * Process @work.  This function contains all the logics necessary to
  * process a single work including synchronization against and
  * interaction with other workers on the same cpu, queueing and
  * flushing.  As long as context requirement is met, any worker can
  * call this function to process a work.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which is released and regrabbed.
  */
 static void process_one_work(struct worker *worker, struct work_struct *work)
 __releases(&pool->lock)
 __acquires(&pool->lock)
 {
     struct pool_workqueue *pwq = get_work_pwq(work);
     struct worker_pool *pool = worker->pool;
     bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
     unsigned long work_data;
     struct worker *collision;
 #ifdef CONFIG_LOCKDEP
     /*
      * It is permissible to free the struct work_struct from
      * inside the function that is called from it, this we need to
      * take into account for lockdep too.  To avoid bogus "held
      * lock freed" warnings as well as problems when looking into
      * work->lockdep_map, make a copy and use that here.
      */
     struct lockdep_map lockdep_map;
 
     lockdep_copy_map(&lockdep_map, &work->lockdep_map);
 #endif
     /* ensure we're on the correct CPU */
     WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
              raw_smp_processor_id() != pool->cpu);
 
     /*
      * A single work shouldn't be executed concurrently by
      * multiple workers on a single cpu.  Check whether anyone is
      * already processing the work.  If so, defer the work to the
      * currently executing one.
      */
     collision = find_worker_executing_work(pool, work);
     if (unlikely(collision)) {
         move_linked_works(work, &collision->scheduled, NULL);
         return;
     }
 
     /* claim and dequeue */
     debug_work_deactivate(work);
     hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
     worker->current_work = work;
     worker->current_func = work->func;
     worker->current_pwq = pwq;
     work_data = *work_data_bits(work);
     worker->current_color = get_work_color(work_data);
 
     /*
      * Record wq name for cmdline and debug reporting, may get
      * overridden through set_worker_desc().
      */
     strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);
 
     list_del_init(&work->entry);
 
     /*
      * CPU intensive works don't participate in concurrency management.
      * They're the scheduler's responsibility.  This takes @worker out
      * of concurrency management and the next code block will chain
      * execution of the pending work items.
      */
     if (unlikely(cpu_intensive))
         worker_set_flags(worker, WORKER_CPU_INTENSIVE);
 
     /*
      * Wake up another worker if necessary.  The condition is always
      * false for normal per-cpu workers since nr_running would always
      * be >= 1 at this point.  This is used to chain execution of the
      * pending work items for WORKER_NOT_RUNNING workers such as the
      * UNBOUND and CPU_INTENSIVE ones.
      */
     if (need_more_worker(pool))
         wake_up_worker(pool);
 
     /*
      * Record the last pool and clear PENDING which should be the last
      * update to @work.  Also, do this inside @pool->lock so that
      * PENDING and queued state changes happen together while IRQ is
      * disabled.
      */
     set_work_pool_and_clear_pending(work, pool->id);
 
     raw_spin_unlock_irq(&pool->lock);
 
     lock_map_acquire(&pwq->wq->lockdep_map);
     lock_map_acquire(&lockdep_map);
     /*
      * Strictly speaking we should mark the invariant state without holding
      * any locks, that is, before these two lock_map_acquire()'s.
      *
      * However, that would result in:
      *
      *   A(W1)
      *   WFC(C)
      *      A(W1)
      *      C(C)
      *
      * Which would create W1->C->W1 dependencies, even though there is no
      * actual deadlock possible. There are two solutions, using a
      * read-recursive acquire on the work(queue) 'locks', but this will then
      * hit the lockdep limitation on recursive locks, or simply discard
      * these locks.
      *
      * AFAICT there is no possible deadlock scenario between the
      * flush_work() and complete() primitives (except for single-threaded
      * workqueues), so hiding them isn't a problem.
      */
     lockdep_invariant_state(true);
     trace_workqueue_execute_start(work);
     worker->current_func(work);
     /*
      * While we must be careful to not use "work" after this, the trace
      * point will only record its address.
      */
     trace_workqueue_execute_end(work, worker->current_func);
     lock_map_release(&lockdep_map);
     lock_map_release(&pwq->wq->lockdep_map);
 
     if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
         pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d\n"
                "     last function: %ps\n",
                current->comm, preempt_count(), task_pid_nr(current),
                worker->current_func);
         debug_show_held_locks(current);
         dump_stack();
     }
 
     /*
      * The following prevents a kworker from hogging CPU on !PREEMPTION
      * kernels, where a requeueing work item waiting for something to
      * happen could deadlock with stop_machine as such work item could
      * indefinitely requeue itself while all other CPUs are trapped in
      * stop_machine. At the same time, report a quiescent RCU state so
      * the same condition doesn't freeze RCU.
      */
     cond_resched();
 
     raw_spin_lock_irq(&pool->lock);
 
     /* clear cpu intensive status */
     if (unlikely(cpu_intensive))
         worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
 
     /* tag the worker for identification in schedule() */
     worker->last_func = worker->current_func;
 
     /* we're done with it, release */
     hash_del(&worker->hentry);
     worker->current_work = NULL;
     worker->current_func = NULL;
     worker->current_pwq = NULL;
     worker->current_color = INT_MAX;
     pwq_dec_nr_in_flight(pwq, work_data);
 }
 
 /**
  * process_scheduled_works - process scheduled works
  * @worker: self
  *
  * Process all scheduled works.  Please note that the scheduled list
  * may change while processing a work, so this function repeatedly
  * fetches a work from the top and executes it.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.
  */
 static void process_scheduled_works(struct worker *worker)
 {
     while (!list_empty(&worker->scheduled)) {
         struct work_struct *work = list_first_entry(&worker->scheduled,
                         struct work_struct, entry);
         process_one_work(worker, work);
     }
 }
 
 static void set_pf_worker(bool val)
 {
     mutex_lock(&wq_pool_attach_mutex);
     if (val)
         current->flags |= PF_WQ_WORKER;
     else
         current->flags &= ~PF_WQ_WORKER;
     mutex_unlock(&wq_pool_attach_mutex);
 }
 
 /**
  * worker_thread - the worker thread function
  * @__worker: self
  *
  * The worker thread function.  All workers belong to a worker_pool -
  * either a per-cpu one or dynamic unbound one.  These workers process all
  * work items regardless of their specific target workqueue.  The only
  * exception is work items which belong to workqueues with a rescuer which
  * will be explained in rescuer_thread().
  *
  * Return: 0
  */
 static int worker_thread(void *__worker)
 {
     struct worker *worker = __worker;
     struct worker_pool *pool = worker->pool;
 
     /* tell the scheduler that this is a workqueue worker */
     set_pf_worker(true);
 woke_up:
     raw_spin_lock_irq(&pool->lock);
 
     /* am I supposed to die? */
     if (unlikely(worker->flags & WORKER_DIE)) {
         raw_spin_unlock_irq(&pool->lock);
         WARN_ON_ONCE(!list_empty(&worker->entry));
         set_pf_worker(false);
 
         set_task_comm(worker->task, "kworker/dying");
         ida_free(&pool->worker_ida, worker->id);
         worker_detach_from_pool(worker);
         kfree(worker);
         return 0;
     }
 
     worker_leave_idle(worker);
 recheck:
     /* no more worker necessary? */
     if (!need_more_worker(pool))
         goto sleep;
 
     /* do we need to manage? */
     if (unlikely(!may_start_working(pool)) && manage_workers(worker))
         goto recheck;
 
     /*
      * ->scheduled list can only be filled while a worker is
      * preparing to process a work or actually processing it.
      * Make sure nobody diddled with it while I was sleeping.
      */
     WARN_ON_ONCE(!list_empty(&worker->scheduled));
 
     /*
      * Finish PREP stage.  We're guaranteed to have at least one idle
      * worker or that someone else has already assumed the manager
      * role.  This is where @worker starts participating in concurrency
      * management if applicable and concurrency management is restored
      * after being rebound.  See rebind_workers() for details.
      */
     worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
 
     do {
         struct work_struct *work =
             list_first_entry(&pool->worklist,
                      struct work_struct, entry);
 
         pool->watchdog_ts = jiffies;
 
         if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
             /* optimization path, not strictly necessary */
             process_one_work(worker, work);
             if (unlikely(!list_empty(&worker->scheduled)))
                 process_scheduled_works(worker);
         } else {
             move_linked_works(work, &worker->scheduled, NULL);
             process_scheduled_works(worker);
         }
     } while (keep_working(pool));
 
     worker_set_flags(worker, WORKER_PREP);
 sleep:
     /*
      * pool->lock is held and there's no work to process and no need to
      * manage, sleep.  Workers are woken up only while holding
      * pool->lock or from local cpu, so setting the current state
      * before releasing pool->lock is enough to prevent losing any
      * event.
      */
     worker_enter_idle(worker);
     __set_current_state(TASK_IDLE);
     raw_spin_unlock_irq(&pool->lock);
     schedule();
     goto woke_up;
 }
 
 /**
  * rescuer_thread - the rescuer thread function
  * @__rescuer: self
  *
  * Workqueue rescuer thread function.  There's one rescuer for each
  * workqueue which has WQ_MEM_RECLAIM set.
  *
  * Regular work processing on a pool may block trying to create a new
  * worker which uses GFP_KERNEL allocation which has slight chance of
  * developing into deadlock if some works currently on the same queue
  * need to be processed to satisfy the GFP_KERNEL allocation.  This is
  * the problem rescuer solves.
  *
  * When such condition is possible, the pool summons rescuers of all
  * workqueues which have works queued on the pool and let them process
  * those works so that forward progress can be guaranteed.
  *
  * This should happen rarely.
  *
  * Return: 0
  */
 static int rescuer_thread(void *__rescuer)
 {
     struct worker *rescuer = __rescuer;
     struct workqueue_struct *wq = rescuer->rescue_wq;
     struct list_head *scheduled = &rescuer->scheduled;
     bool should_stop;
 
     set_user_nice(current, RESCUER_NICE_LEVEL);
 
     /*
      * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
      * doesn't participate in concurrency management.
      */
     set_pf_worker(true);
 repeat:
     set_current_state(TASK_IDLE);
 
     /*
      * By the time the rescuer is requested to stop, the workqueue
      * shouldn't have any work pending, but @wq->maydays may still have
      * pwq(s) queued.  This can happen by non-rescuer workers consuming
      * all the work items before the rescuer got to them.  Go through
      * @wq->maydays processing before acting on should_stop so that the
      * list is always empty on exit.
      */
     should_stop = kthread_should_stop();
 
     /* see whether any pwq is asking for help */
     raw_spin_lock_irq(&wq_mayday_lock);
 
     while (!list_empty(&wq->maydays)) {
         struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
                     struct pool_workqueue, mayday_node);
         struct worker_pool *pool = pwq->pool;
         struct work_struct *work, *n;
         bool first = true;
 
         __set_current_state(TASK_RUNNING);
         list_del_init(&pwq->mayday_node);
 
         raw_spin_unlock_irq(&wq_mayday_lock);
 
         worker_attach_to_pool(rescuer, pool);
 
         raw_spin_lock_irq(&pool->lock);
 
         /*
          * Slurp in all works issued via this workqueue and
          * process'em.
          */
         WARN_ON_ONCE(!list_empty(scheduled));
         list_for_each_entry_safe(work, n, &pool->worklist, entry) {
             if (get_work_pwq(work) == pwq) {
                 if (first)
                     pool->watchdog_ts = jiffies;
                 move_linked_works(work, scheduled, &n);
             }
             first = false;
         }
 
         if (!list_empty(scheduled)) {
             process_scheduled_works(rescuer);
 
             /*
              * The above execution of rescued work items could
              * have created more to rescue through
              * pwq_activate_first_inactive() or chained
              * queueing.  Let's put @pwq back on mayday list so
              * that such back-to-back work items, which may be
              * being used to relieve memory pressure, don't
              * incur MAYDAY_INTERVAL delay inbetween.
              */
             if (pwq->nr_active && need_to_create_worker(pool)) {
                 raw_spin_lock(&wq_mayday_lock);
                 /*
                  * Queue iff we aren't racing destruction
                  * and somebody else hasn't queued it already.
                  */
                 if (wq->rescuer && list_empty(&pwq->mayday_node)) {
                     get_pwq(pwq);
                     list_add_tail(&pwq->mayday_node, &wq->maydays);
                 }
                 raw_spin_unlock(&wq_mayday_lock);
             }
         }
 
         /*
          * Put the reference grabbed by send_mayday().  @pool won't
          * go away while we're still attached to it.
          */
         put_pwq(pwq);
 
         /*
          * Leave this pool.  If need_more_worker() is %true, notify a
          * regular worker; otherwise, we end up with 0 concurrency
          * and stalling the execution.
          */
         if (need_more_worker(pool))
             wake_up_worker(pool);
 
         raw_spin_unlock_irq(&pool->lock);
 
         worker_detach_from_pool(rescuer);
 
         raw_spin_lock_irq(&wq_mayday_lock);
     }
 
     raw_spin_unlock_irq(&wq_mayday_lock);
 
     if (should_stop) {
         __set_current_state(TASK_RUNNING);
         set_pf_worker(false);
         return 0;
     }
 
     /* rescuers should never participate in concurrency management */
     WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
     schedule();
     goto repeat;
 }
 
 /**
  * check_flush_dependency - check for flush dependency sanity
  * @target_wq: workqueue being flushed
  * @target_work: work item being flushed (NULL for workqueue flushes)
  *
  * %current is trying to flush the whole @target_wq or @target_work on it.
  * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
  * reclaiming memory or running on a workqueue which doesn't have
  * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
  * a deadlock.
  */
 static void check_flush_dependency(struct workqueue_struct *target_wq,
                    struct work_struct *target_work)
 {
     work_func_t target_func = target_work ? target_work->func : NULL;
     struct worker *worker;
 
     if (target_wq->flags & WQ_MEM_RECLAIM)
         return;
 
     worker = current_wq_worker();
 
     WARN_ONCE(current->flags & PF_MEMALLOC,
           "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%ps",
           current->pid, current->comm, target_wq->name, target_func);
     WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
                   (WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
           "workqueue: WQ_MEM_RECLAIM %s:%ps is flushing !WQ_MEM_RECLAIM %s:%ps",
           worker->current_pwq->wq->name, worker->current_func,
           target_wq->name, target_func);
 }
 
 struct wq_barrier {
     struct work_struct  work;
     struct completion   done;
     struct task_struct  *task;  /* purely informational */
 };
 
 static void wq_barrier_func(struct work_struct *work)
 {
     struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
     complete(&barr->done);
 }
 
 /**
  * insert_wq_barrier - insert a barrier work
  * @pwq: pwq to insert barrier into
  * @barr: wq_barrier to insert
  * @target: target work to attach @barr to
  * @worker: worker currently executing @target, NULL if @target is not executing
  *
  * @barr is linked to @target such that @barr is completed only after
  * @target finishes execution.  Please note that the ordering
  * guarantee is observed only with respect to @target and on the local
  * cpu.
  *
  * Currently, a queued barrier can't be canceled.  This is because
  * try_to_grab_pending() can't determine whether the work to be
  * grabbed is at the head of the queue and thus can't clear LINKED
  * flag of the previous work while there must be a valid next work
  * after a work with LINKED flag set.
  *
  * Note that when @worker is non-NULL, @target may be modified
  * underneath us, so we can't reliably determine pwq from @target.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void insert_wq_barrier(struct pool_workqueue *pwq,
                   struct wq_barrier *barr,
                   struct work_struct *target, struct worker *worker)
 {
     unsigned int work_flags = 0;
     unsigned int work_color;
     struct list_head *head;
 
     /*
      * debugobject calls are safe here even with pool->lock locked
      * as we know for sure that this will not trigger any of the
      * checks and call back into the fixup functions where we
      * might deadlock.
      */
     INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
     __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
 
     init_completion_map(&barr->done, &target->lockdep_map);
 
     barr->task = current;
 
     /* The barrier work item does not participate in pwq->nr_active. */
     work_flags |= WORK_STRUCT_INACTIVE;
 
     /*
      * If @target is currently being executed, schedule the
      * barrier to the worker; otherwise, put it after @target.
      */
     if (worker) {
         head = worker->scheduled.next;
         work_color = worker->current_color;
     } else {
         unsigned long *bits = work_data_bits(target);
 
         head = target->entry.next;
         /* there can already be other linked works, inherit and set */
         work_flags |= *bits & WORK_STRUCT_LINKED;
         work_color = get_work_color(*bits);
         __set_bit(WORK_STRUCT_LINKED_BIT, bits);
     }
 
     pwq->nr_in_flight[work_color]++;
     work_flags |= work_color_to_flags(work_color);
 
     debug_work_activate(&barr->work);
     insert_work(pwq, &barr->work, head, work_flags);
 }
 
 /**
  * flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
  * @wq: workqueue being flushed
  * @flush_color: new flush color, < 0 for no-op
  * @work_color: new work color, < 0 for no-op
  *
  * Prepare pwqs for workqueue flushing.
  *
  * If @flush_color is non-negative, flush_color on all pwqs should be
  * -1.  If no pwq has in-flight commands at the specified color, all
  * pwq->flush_color's stay at -1 and %false is returned.  If any pwq
  * has in flight commands, its pwq->flush_color is set to
  * @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
  * wakeup logic is armed and %true is returned.
  *
  * The caller should have initialized @wq->first_flusher prior to
  * calling this function with non-negative @flush_color.  If
  * @flush_color is negative, no flush color update is done and %false
  * is returned.
  *
  * If @work_color is non-negative, all pwqs should have the same
  * work_color which is previous to @work_color and all will be
  * advanced to @work_color.
  *
  * CONTEXT:
  * mutex_lock(wq->mutex).
  *
  * Return:
  * %true if @flush_color >= 0 and there's something to flush.  %false
  * otherwise.
  */
 static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
                       int flush_color, int work_color)
 {
     bool wait = false;
     struct pool_workqueue *pwq;
 
     if (flush_color >= 0) {
         WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
         atomic_set(&wq->nr_pwqs_to_flush, 1);
     }
 
     for_each_pwq(pwq, wq) {
         struct worker_pool *pool = pwq->pool;
 
         raw_spin_lock_irq(&pool->lock);
 
         if (flush_color >= 0) {
             WARN_ON_ONCE(pwq->flush_color != -1);
 
             if (pwq->nr_in_flight[flush_color]) {
                 pwq->flush_color = flush_color;
                 atomic_inc(&wq->nr_pwqs_to_flush);
                 wait = true;
             }
         }
 
         if (work_color >= 0) {
             WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
             pwq->work_color = work_color;
         }
 
         raw_spin_unlock_irq(&pool->lock);
     }
 
     if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
         complete(&wq->first_flusher->done);
 
     return wait;
 }
 
 /**
  * __flush_workqueue - ensure that any scheduled work has run to completion.
  * @wq: workqueue to flush
  *
  * This function sleeps until all work items which were queued on entry
  * have finished execution, but it is not livelocked by new incoming ones.
  */
 void __flush_workqueue(struct workqueue_struct *wq)
 {
     struct wq_flusher this_flusher = {
         .list = LIST_HEAD_INIT(this_flusher.list),
         .flush_color = -1,
         .done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, wq->lockdep_map),
     };
     int next_color;
 
     if (WARN_ON(!wq_online))
         return;
 
     lock_map_acquire(&wq->lockdep_map);
     lock_map_release(&wq->lockdep_map);
 
     mutex_lock(&wq->mutex);
 
     /*
      * Start-to-wait phase
      */
     next_color = work_next_color(wq->work_color);
 
     if (next_color != wq->flush_color) {
         /*
          * Color space is not full.  The current work_color
          * becomes our flush_color and work_color is advanced
          * by one.
          */
         WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
         this_flusher.flush_color = wq->work_color;
         wq->work_color = next_color;
 
         if (!wq->first_flusher) {
             /* no flush in progress, become the first flusher */
             WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
 
             wq->first_flusher = &this_flusher;
 
             if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
                                wq->work_color)) {
                 /* nothing to flush, done */
                 wq->flush_color = next_color;
                 wq->first_flusher = NULL;
                 goto out_unlock;
             }
         } else {
             /* wait in queue */
             WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
             list_add_tail(&this_flusher.list, &wq->flusher_queue);
             flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
         }
     } else {
         /*
          * Oops, color space is full, wait on overflow queue.
          * The next flush completion will assign us
          * flush_color and transfer to flusher_queue.
          */
         list_add_tail(&this_flusher.list, &wq->flusher_overflow);
     }
 
     check_flush_dependency(wq, NULL);
 
     mutex_unlock(&wq->mutex);
 
     wait_for_completion(&this_flusher.done);
 
     /*
      * Wake-up-and-cascade phase
      *
      * First flushers are responsible for cascading flushes and
      * handling overflow.  Non-first flushers can simply return.
      */
     if (READ_ONCE(wq->first_flusher) != &this_flusher)
         return;
 
     mutex_lock(&wq->mutex);
 
     /* we might have raced, check again with mutex held */
     if (wq->first_flusher != &this_flusher)
         goto out_unlock;
 
     WRITE_ONCE(wq->first_flusher, NULL);
 
     WARN_ON_ONCE(!list_empty(&this_flusher.list));
     WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
 
     while (true) {
         struct wq_flusher *next, *tmp;
 
         /* complete all the flushers sharing the current flush color */
         list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
             if (next->flush_color != wq->flush_color)
                 break;
             list_del_init(&next->list);
             complete(&next->done);
         }
 
         WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
                  wq->flush_color != work_next_color(wq->work_color));
 
         /* this flush_color is finished, advance by one */
         wq->flush_color = work_next_color(wq->flush_color);
 
         /* one color has been freed, handle overflow queue */
         if (!list_empty(&wq->flusher_overflow)) {
             /*
              * Assign the same color to all overflowed
              * flushers, advance work_color and append to
              * flusher_queue.  This is the start-to-wait
              * phase for these overflowed flushers.
              */
             list_for_each_entry(tmp, &wq->flusher_overflow, list)
                 tmp->flush_color = wq->work_color;
 
             wq->work_color = work_next_color(wq->work_color);
 
             list_splice_tail_init(&wq->flusher_overflow,
                           &wq->flusher_queue);
             flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
         }
 
         if (list_empty(&wq->flusher_queue)) {
             WARN_ON_ONCE(wq->flush_color != wq->work_color);
             break;
         }
 
         /*
          * Need to flush more colors.  Make the next flusher
          * the new first flusher and arm pwqs.
          */
         WARN_ON_ONCE(wq->flush_color == wq->work_color);
         WARN_ON_ONCE(wq->flush_color != next->flush_color);
 
         list_del_init(&next->list);
         wq->first_flusher = next;
 
         if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
             break;
 
         /*
          * Meh... this color is already done, clear first
          * flusher and repeat cascading.
          */
         wq->first_flusher = NULL;
     }
 
 out_unlock:
     mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL(__flush_workqueue);
 
 /**
  * drain_workqueue - drain a workqueue
  * @wq: workqueue to drain
  *
  * Wait until the workqueue becomes empty.  While draining is in progress,
  * only chain queueing is allowed.  IOW, only currently pending or running
  * work items on @wq can queue further work items on it.  @wq is flushed
  * repeatedly until it becomes empty.  The number of flushing is determined
  * by the depth of chaining and should be relatively short.  Whine if it
  * takes too long.
  */
 void drain_workqueue(struct workqueue_struct *wq)
 {
     unsigned int flush_cnt = 0;
     struct pool_workqueue *pwq;
 
     /*
      * __queue_work() needs to test whether there are drainers, is much
      * hotter than drain_workqueue() and already looks at @wq->flags.
      * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
      */
     mutex_lock(&wq->mutex);
     if (!wq->nr_drainers++)
         wq->flags |= __WQ_DRAINING;
     mutex_unlock(&wq->mutex);
 reflush:
     __flush_workqueue(wq);
 
     mutex_lock(&wq->mutex);
 
     for_each_pwq(pwq, wq) {
         bool drained;
 
         raw_spin_lock_irq(&pwq->pool->lock);
         drained = !pwq->nr_active && list_empty(&pwq->inactive_works);
         raw_spin_unlock_irq(&pwq->pool->lock);
 
         if (drained)
             continue;
 
         if (++flush_cnt == 10 ||
             (flush_cnt % 100 == 0 && flush_cnt <= 1000))
             pr_warn("workqueue %s: %s() isn't complete after %u tries\n",
                 wq->name, __func__, flush_cnt);
 
         mutex_unlock(&wq->mutex);
         goto reflush;
     }
 
     if (!--wq->nr_drainers)
         wq->flags &= ~__WQ_DRAINING;
     mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL_GPL(drain_workqueue);
 
 static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
                  bool from_cancel)
 {
     struct worker *worker = NULL;
     struct worker_pool *pool;
     struct pool_workqueue *pwq;
 
     might_sleep();
 
     rcu_read_lock();
     pool = get_work_pool(work);
     if (!pool) {
         rcu_read_unlock();
         return false;
     }
 
     raw_spin_lock_irq(&pool->lock);
     /* see the comment in try_to_grab_pending() with the same code */
     pwq = get_work_pwq(work);
     if (pwq) {
         if (unlikely(pwq->pool != pool))
             goto already_gone;
     } else {
         worker = find_worker_executing_work(pool, work);
         if (!worker)
             goto already_gone;
         pwq = worker->current_pwq;
     }
 
     check_flush_dependency(pwq->wq, work);
 
     insert_wq_barrier(pwq, barr, work, worker);
     raw_spin_unlock_irq(&pool->lock);
 
     /*
      * Force a lock recursion deadlock when using flush_work() inside a
      * single-threaded or rescuer equipped workqueue.
      *
      * For single threaded workqueues the deadlock happens when the work
      * is after the work issuing the flush_work(). For rescuer equipped
      * workqueues the deadlock happens when the rescuer stalls, blocking
      * forward progress.
      */
     if (!from_cancel &&
         (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)) {
         lock_map_acquire(&pwq->wq->lockdep_map);
         lock_map_release(&pwq->wq->lockdep_map);
     }
     rcu_read_unlock();
     return true;
 already_gone:
     raw_spin_unlock_irq(&pool->lock);
     rcu_read_unlock();
     return false;
 }
 
 static bool __flush_work(struct work_struct *work, bool from_cancel)
 {
     struct wq_barrier barr;
 
     if (WARN_ON(!wq_online))
         return false;
 
     if (WARN_ON(!work->func))
         return false;
 
     lock_map_acquire(&work->lockdep_map);
     lock_map_release(&work->lockdep_map);
 
     if (start_flush_work(work, &barr, from_cancel)) {
         wait_for_completion(&barr.done);
         destroy_work_on_stack(&barr.work);
         return true;
     } else {
         return false;
     }
 }
 
 /**
  * flush_work - wait for a work to finish executing the last queueing instance
  * @work: the work to flush
  *
  * Wait until @work has finished execution.  @work is guaranteed to be idle
  * on return if it hasn't been requeued since flush started.
  *
  * Return:
  * %true if flush_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_work(struct work_struct *work)
 {
     return __flush_work(work, false);
 }
 EXPORT_SYMBOL_GPL(flush_work);
 
 struct cwt_wait {
     wait_queue_entry_t      wait;
     struct work_struct  *work;
 };
 
 static int cwt_wakefn(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
 {
     struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait);
 
     if (cwait->work != key)
         return 0;
     return autoremove_wake_function(wait, mode, sync, key);
 }
 
 static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
 {
     static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq);
     unsigned long flags;
     int ret;
 
     do {
         ret = try_to_grab_pending(work, is_dwork, &flags);
         /*
          * If someone else is already canceling, wait for it to
          * finish.  flush_work() doesn't work for PREEMPT_NONE
          * because we may get scheduled between @work's completion
          * and the other canceling task resuming and clearing
          * CANCELING - flush_work() will return false immediately
          * as @work is no longer busy, try_to_grab_pending() will
          * return -ENOENT as @work is still being canceled and the
          * other canceling task won't be able to clear CANCELING as
          * we're hogging the CPU.
          *
          * Let's wait for completion using a waitqueue.  As this
          * may lead to the thundering herd problem, use a custom
          * wake function which matches @work along with exclusive
          * wait and wakeup.
          */
         if (unlikely(ret == -ENOENT)) {
             struct cwt_wait cwait;
 
             init_wait(&cwait.wait);
             cwait.wait.func = cwt_wakefn;
             cwait.work = work;
 
             prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait,
                           TASK_UNINTERRUPTIBLE);
             if (work_is_canceling(work))
                 schedule();
             finish_wait(&cancel_waitq, &cwait.wait);
         }
     } while (unlikely(ret < 0));
 
     /* tell other tasks trying to grab @work to back off */
     mark_work_canceling(work);
     local_irq_restore(flags);
 
     /*
      * This allows canceling during early boot.  We know that @work
      * isn't executing.
      */
     if (wq_online)
         __flush_work(work, true);
 
     clear_work_data(work);
 
     /*
      * Paired with prepare_to_wait() above so that either
      * waitqueue_active() is visible here or !work_is_canceling() is
      * visible there.
      */
     smp_mb();
     if (waitqueue_active(&cancel_waitq))
         __wake_up(&cancel_waitq, TASK_NORMAL, 1, work);
 
     return ret;
 }
 
 /**
  * cancel_work_sync - cancel a work and wait for it to finish
  * @work: the work to cancel
  *
  * Cancel @work and wait for its execution to finish.  This function
  * can be used even if the work re-queues itself or migrates to
  * another workqueue.  On return from this function, @work is
  * guaranteed to be not pending or executing on any CPU.
  *
  * cancel_work_sync(&delayed_work->work) must not be used for
  * delayed_work's.  Use cancel_delayed_work_sync() instead.
  *
  * The caller must ensure that the workqueue on which @work was last
  * queued can't be destroyed before this function returns.
  *
  * Return:
  * %true if @work was pending, %false otherwise.
  */
 bool cancel_work_sync(struct work_struct *work)
 {
     return __cancel_work_timer(work, false);
 }
 EXPORT_SYMBOL_GPL(cancel_work_sync);
 
 /**
  * flush_delayed_work - wait for a dwork to finish executing the last queueing
  * @dwork: the delayed work to flush
  *
  * Delayed timer is cancelled and the pending work is queued for
  * immediate execution.  Like flush_work(), this function only
  * considers the last queueing instance of @dwork.
  *
  * Return:
  * %true if flush_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_delayed_work(struct delayed_work *dwork)
 {
     local_irq_disable();
     if (del_timer_sync(&dwork->timer))
         __queue_work(dwork->cpu, dwork->wq, &dwork->work);
     local_irq_enable();
     return flush_work(&dwork->work);
 }
 EXPORT_SYMBOL(flush_delayed_work);
 
 /**
  * flush_rcu_work - wait for a rwork to finish executing the last queueing
  * @rwork: the rcu work to flush
  *
  * Return:
  * %true if flush_rcu_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_rcu_work(struct rcu_work *rwork)
 {
     if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
         rcu_barrier();
         flush_work(&rwork->work);
         return true;
     } else {
         return flush_work(&rwork->work);
     }
 }
 EXPORT_SYMBOL(flush_rcu_work);
 
 static bool __cancel_work(struct work_struct *work, bool is_dwork)
 {
     unsigned long flags;
     int ret;
 
     do {
         ret = try_to_grab_pending(work, is_dwork, &flags);
     } while (unlikely(ret == -EAGAIN));
 
     if (unlikely(ret < 0))
         return false;
 
     set_work_pool_and_clear_pending(work, get_work_pool_id(work));
     local_irq_restore(flags);
     return ret;
 }
 
 /*
  * See cancel_delayed_work()
  */
 bool cancel_work(struct work_struct *work)
 {
     return __cancel_work(work, false);
 }
 EXPORT_SYMBOL(cancel_work);
 
 /**
  * cancel_delayed_work - cancel a delayed work
  * @dwork: delayed_work to cancel
  *
  * Kill off a pending delayed_work.
  *
  * Return: %true if @dwork was pending and canceled; %false if it wasn't
  * pending.
  *
  * Note:
  * The work callback function may still be running on return, unless
  * it returns %true and the work doesn't re-arm itself.  Explicitly flush or
  * use cancel_delayed_work_sync() to wait on it.
  *
  * This function is safe to call from any context including IRQ handler.
  */
 bool cancel_delayed_work(struct delayed_work *dwork)
 {
     return __cancel_work(&dwork->work, true);
 }
 EXPORT_SYMBOL(cancel_delayed_work);
 
 /**
  * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
  * @dwork: the delayed work cancel
  *
  * This is cancel_work_sync() for delayed works.
  *
  * Return:
  * %true if @dwork was pending, %false otherwise.
  */
 bool cancel_delayed_work_sync(struct delayed_work *dwork)
 {
     return __cancel_work_timer(&dwork->work, true);
 }
 EXPORT_SYMBOL(cancel_delayed_work_sync);
 
 /**
  * schedule_on_each_cpu - execute a function synchronously on each online CPU
  * @func: the function to call
  *
  * schedule_on_each_cpu() executes @func on each online CPU using the
  * system workqueue and blocks until all CPUs have completed.
  * schedule_on_each_cpu() is very slow.
  *
  * Return:
  * 0 on success, -errno on failure.
  */
 int schedule_on_each_cpu(work_func_t func)
 {
     int cpu;
     struct work_struct __percpu *works;
 
     works = alloc_percpu(struct work_struct);
     if (!works)
         return -ENOMEM;
 
     cpus_read_lock();
 
     for_each_online_cpu(cpu) {
         struct work_struct *work = per_cpu_ptr(works, cpu);
 
         INIT_WORK(work, func);
         schedule_work_on(cpu, work);
     }
 
     for_each_online_cpu(cpu)
         flush_work(per_cpu_ptr(works, cpu));
 
     cpus_read_unlock();
     free_percpu(works);
     return 0;
 }
 
 /**
  * execute_in_process_context - reliably execute the routine with user context
  * @fn:     the function to execute
  * @ew:     guaranteed storage for the execute work structure (must
  *      be available when the work executes)
  *
  * Executes the function immediately if process context is available,
  * otherwise schedules the function for delayed execution.
  *
  * Return:  0 - function was executed
  *      1 - function was scheduled for execution
  */
 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 {
     if (!in_interrupt()) {
         fn(&ew->work);
         return 0;
     }
 
     INIT_WORK(&ew->work, fn);
     schedule_work(&ew->work);
 
     return 1;
 }
 EXPORT_SYMBOL_GPL(execute_in_process_context);
 
 /**
  * free_workqueue_attrs - free a workqueue_attrs
  * @attrs: workqueue_attrs to free
  *
  * Undo alloc_workqueue_attrs().
  */
 void free_workqueue_attrs(struct workqueue_attrs *attrs)
 {
     if (attrs) {
         free_cpumask_var(attrs->cpumask);
         kfree(attrs);
     }
 }
 
 /**
  * alloc_workqueue_attrs - allocate a workqueue_attrs
  *
  * Allocate a new workqueue_attrs, initialize with default settings and
  * return it.
  *
  * Return: The allocated new workqueue_attr on success. %NULL on failure.
  */
 struct workqueue_attrs *alloc_workqueue_attrs(void)
 {
     struct workqueue_attrs *attrs;
 
     attrs = kzalloc(sizeof(*attrs), GFP_KERNEL);
     if (!attrs)
         goto fail;
     if (!alloc_cpumask_var(&attrs->cpumask, GFP_KERNEL))
         goto fail;
 
     cpumask_copy(attrs->cpumask, cpu_possible_mask);
     return attrs;
 fail:
     free_workqueue_attrs(attrs);
     return NULL;
 }
 
 static void copy_workqueue_attrs(struct workqueue_attrs *to,
                  const struct workqueue_attrs *from)
 {
     to->nice = from->nice;
     cpumask_copy(to->cpumask, from->cpumask);
     /*
      * Unlike hash and equality test, this function doesn't ignore
      * ->no_numa as it is used for both pool and wq attrs.  Instead,
      * get_unbound_pool() explicitly clears ->no_numa after copying.
      */
     to->no_numa = from->no_numa;
 }
 
 /* hash value of the content of @attr */
 static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
 {
     u32 hash = 0;
 
     hash = jhash_1word(attrs->nice, hash);
     hash = jhash(cpumask_bits(attrs->cpumask),
              BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
     return hash;
 }
 
 /* content equality test */
 static bool wqattrs_equal(const struct workqueue_attrs *a,
               const struct workqueue_attrs *b)
 {
     if (a->nice != b->nice)
         return false;
     if (!cpumask_equal(a->cpumask, b->cpumask))
         return false;
     return true;
 }
 
 /**
  * init_worker_pool - initialize a newly zalloc'd worker_pool
  * @pool: worker_pool to initialize
  *
  * Initialize a newly zalloc'd @pool.  It also allocates @pool->attrs.
  *
  * Return: 0 on success, -errno on failure.  Even on failure, all fields
  * inside @pool proper are initialized and put_unbound_pool() can be called
  * on @pool safely to release it.
  */
 static int init_worker_pool(struct worker_pool *pool)
 {
     raw_spin_lock_init(&pool->lock);
     pool->id = -1;
     pool->cpu = -1;
     pool->node = NUMA_NO_NODE;
     pool->flags |= POOL_DISASSOCIATED;
     pool->watchdog_ts = jiffies;
     INIT_LIST_HEAD(&pool->worklist);
     INIT_LIST_HEAD(&pool->idle_list);
     hash_init(pool->busy_hash);
 
     timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE);
 
     timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);
 
     INIT_LIST_HEAD(&pool->workers);
 
     ida_init(&pool->worker_ida);
     INIT_HLIST_NODE(&pool->hash_node);
     pool->refcnt = 1;
 
     /* shouldn't fail above this point */
     pool->attrs = alloc_workqueue_attrs();
     if (!pool->attrs)
         return -ENOMEM;
     return 0;
 }
 
 #ifdef CONFIG_LOCKDEP
 static void wq_init_lockdep(struct workqueue_struct *wq)
 {
     char *lock_name;
 
     lockdep_register_key(&wq->key);
     lock_name = kasprintf(GFP_KERNEL, "%s%s", "(wq_completion)", wq->name);
     if (!lock_name)
         lock_name = wq->name;
 
     wq->lock_name = lock_name;
     lockdep_init_map(&wq->lockdep_map, lock_name, &wq->key, 0);
 }
 
 static void wq_unregister_lockdep(struct workqueue_struct *wq)
 {
     lockdep_unregister_key(&wq->key);
 }
 
 static void wq_free_lockdep(struct workqueue_struct *wq)
 {
     if (wq->lock_name != wq->name)
         kfree(wq->lock_name);
 }
 #else
 static void wq_init_lockdep(struct workqueue_struct *wq)
 {
 }
 
 static void wq_unregister_lockdep(struct workqueue_struct *wq)
 {
 }
 
 static void wq_free_lockdep(struct workqueue_struct *wq)
 {
 }
 #endif
 
 static void rcu_free_wq(struct rcu_head *rcu)
 {
     struct workqueue_struct *wq =
         container_of(rcu, struct workqueue_struct, rcu);
 
     wq_free_lockdep(wq);
 
     if (!(wq->flags & WQ_UNBOUND))
         free_percpu(wq->cpu_pwqs);
     else
         free_workqueue_attrs(wq->unbound_attrs);
 
     kfree(wq);
 }
 
 static void rcu_free_pool(struct rcu_head *rcu)
 {
     struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
 
     ida_destroy(&pool->worker_ida);
     free_workqueue_attrs(pool->attrs);
     kfree(pool);
 }
 
 /* This returns with the lock held on success (pool manager is inactive). */
 static bool wq_manager_inactive(struct worker_pool *pool)
 {
     raw_spin_lock_irq(&pool->lock);
 
     if (pool->flags & POOL_MANAGER_ACTIVE) {
         raw_spin_unlock_irq(&pool->lock);
         return false;
     }
     return true;
 }
 
 /**
  * put_unbound_pool - put a worker_pool
  * @pool: worker_pool to put
  *
  * Put @pool.  If its refcnt reaches zero, it gets destroyed in RCU
  * safe manner.  get_unbound_pool() calls this function on its failure path
  * and this function should be able to release pools which went through,
  * successfully or not, init_worker_pool().
  *
  * Should be called with wq_pool_mutex held.
  */
 static void put_unbound_pool(struct worker_pool *pool)
 {
     DECLARE_COMPLETION_ONSTACK(detach_completion);
     struct worker *worker;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     if (--pool->refcnt)
         return;
 
     /* sanity checks */
     if (WARN_ON(!(pool->cpu < 0)) ||
         WARN_ON(!list_empty(&pool->worklist)))
         return;
 
     /* release id and unhash */
     if (pool->id >= 0)
         idr_remove(&worker_pool_idr, pool->id);
     hash_del(&pool->hash_node);
 
     /*
      * Become the manager and destroy all workers.  This prevents
      * @pool's workers from blocking on attach_mutex.  We're the last
      * manager and @pool gets freed with the flag set.
      * Because of how wq_manager_inactive() works, we will hold the
      * spinlock after a successful wait.
      */
     rcuwait_wait_event(&manager_wait, wq_manager_inactive(pool),
                TASK_UNINTERRUPTIBLE);
     pool->flags |= POOL_MANAGER_ACTIVE;
 
     while ((worker = first_idle_worker(pool)))
         destroy_worker(worker);
     WARN_ON(pool->nr_workers || pool->nr_idle);
     raw_spin_unlock_irq(&pool->lock);
 
     mutex_lock(&wq_pool_attach_mutex);
     if (!list_empty(&pool->workers))
         pool->detach_completion = &detach_completion;
     mutex_unlock(&wq_pool_attach_mutex);
 
     if (pool->detach_completion)
         wait_for_completion(pool->detach_completion);
 
     /* shut down the timers */
     del_timer_sync(&pool->idle_timer);
     del_timer_sync(&pool->mayday_timer);
 
     /* RCU protected to allow dereferences from get_work_pool() */
     call_rcu(&pool->rcu, rcu_free_pool);
 }
 
 /**
  * get_unbound_pool - get a worker_pool with the specified attributes
  * @attrs: the attributes of the worker_pool to get
  *
  * Obtain a worker_pool which has the same attributes as @attrs, bump the
  * reference count and return it.  If there already is a matching
  * worker_pool, it will be used; otherwise, this function attempts to
  * create a new one.
  *
  * Should be called with wq_pool_mutex held.
  *
  * Return: On success, a worker_pool with the same attributes as @attrs.
  * On failure, %NULL.
  */
 static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 {
     u32 hash = wqattrs_hash(attrs);
     struct worker_pool *pool;
     int node;
     int target_node = NUMA_NO_NODE;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     /* do we already have a matching pool? */
     hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
         if (wqattrs_equal(pool->attrs, attrs)) {
             pool->refcnt++;
             return pool;
         }
     }
 
     /* if cpumask is contained inside a NUMA node, we belong to that node */
     if (wq_numa_enabled) {
         for_each_node(node) {
             if (cpumask_subset(attrs->cpumask,
                        wq_numa_possible_cpumask[node])) {
                 target_node = node;
                 break;
             }
         }
     }
 
     /* nope, create a new one */
     pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, target_node);
     if (!pool || init_worker_pool(pool) < 0)
         goto fail;
 
     lockdep_set_subclass(&pool->lock, 1);   /* see put_pwq() */
     copy_workqueue_attrs(pool->attrs, attrs);
     pool->node = target_node;
 
     /*
      * no_numa isn't a worker_pool attribute, always clear it.  See
      * 'struct workqueue_attrs' comments for detail.
      */
     pool->attrs->no_numa = false;
 
     if (worker_pool_assign_id(pool) < 0)
         goto fail;
 
     /* create and start the initial worker */
     if (wq_online && !create_worker(pool))
         goto fail;
 
     /* install */
     hash_add(unbound_pool_hash, &pool->hash_node, hash);
 
     return pool;
 fail:
     if (pool)
         put_unbound_pool(pool);
     return NULL;
 }
 
 static void rcu_free_pwq(struct rcu_head *rcu)
 {
     kmem_cache_free(pwq_cache,
             container_of(rcu, struct pool_workqueue, rcu));
 }
 
 /*
  * Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
  * and needs to be destroyed.
  */
 static void pwq_unbound_release_workfn(struct work_struct *work)
 {
     struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
                           unbound_release_work);
     struct workqueue_struct *wq = pwq->wq;
     struct worker_pool *pool = pwq->pool;
     bool is_last = false;
 
     /*
      * when @pwq is not linked, it doesn't hold any reference to the
      * @wq, and @wq is invalid to access.
      */
     if (!list_empty(&pwq->pwqs_node)) {
         if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
             return;
 
         mutex_lock(&wq->mutex);
         list_del_rcu(&pwq->pwqs_node);
         is_last = list_empty(&wq->pwqs);
         mutex_unlock(&wq->mutex);
     }
 
     mutex_lock(&wq_pool_mutex);
     put_unbound_pool(pool);
     mutex_unlock(&wq_pool_mutex);
 
     call_rcu(&pwq->rcu, rcu_free_pwq);
 
     /*
      * If we're the last pwq going away, @wq is already dead and no one
      * is gonna access it anymore.  Schedule RCU free.
      */
     if (is_last) {
         wq_unregister_lockdep(wq);
         call_rcu(&wq->rcu, rcu_free_wq);
     }
 }
 
 /**
  * pwq_adjust_max_active - update a pwq's max_active to the current setting
  * @pwq: target pool_workqueue
  *
  * If @pwq isn't freezing, set @pwq->max_active to the associated
  * workqueue's saved_max_active and activate inactive work items
  * accordingly.  If @pwq is freezing, clear @pwq->max_active to zero.
  */
 static void pwq_adjust_max_active(struct pool_workqueue *pwq)
 {
     struct workqueue_struct *wq = pwq->wq;
     bool freezable = wq->flags & WQ_FREEZABLE;
     unsigned long flags;
 
     /* for @wq->saved_max_active */
     lockdep_assert_held(&wq->mutex);
 
     /* fast exit for non-freezable wqs */
     if (!freezable && pwq->max_active == wq->saved_max_active)
         return;
 
     /* this function can be called during early boot w/ irq disabled */
     raw_spin_lock_irqsave(&pwq->pool->lock, flags);
 
     /*
      * During [un]freezing, the caller is responsible for ensuring that
      * this function is called at least once after @workqueue_freezing
      * is updated and visible.
      */
     if (!freezable || !workqueue_freezing) {
         bool kick = false;
 
         pwq->max_active = wq->saved_max_active;
 
         while (!list_empty(&pwq->inactive_works) &&
                pwq->nr_active < pwq->max_active) {
             pwq_activate_first_inactive(pwq);
             kick = true;
         }
 
         /*
          * Need to kick a worker after thawed or an unbound wq's
          * max_active is bumped. In realtime scenarios, always kicking a
          * worker will cause interference on the isolated cpu cores, so
          * let's kick iff work items were activated.
          */
         if (kick)
             wake_up_worker(pwq->pool);
     } else {
         pwq->max_active = 0;
     }
 
     raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
 }
 
 /* initialize newly allocated @pwq which is associated with @wq and @pool */
 static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
              struct worker_pool *pool)
 {
     BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);
 
     memset(pwq, 0, sizeof(*pwq));
 
     pwq->pool = pool;
     pwq->wq = wq;
     pwq->flush_color = -1;
     pwq->refcnt = 1;
     INIT_LIST_HEAD(&pwq->inactive_works);
     INIT_LIST_HEAD(&pwq->pwqs_node);
     INIT_LIST_HEAD(&pwq->mayday_node);
     INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
 }
 
 /* sync @pwq with the current state of its associated wq and link it */
 static void link_pwq(struct pool_workqueue *pwq)
 {
     struct workqueue_struct *wq = pwq->wq;
 
     lockdep_assert_held(&wq->mutex);
 
     /* may be called multiple times, ignore if already linked */
     if (!list_empty(&pwq->pwqs_node))
         return;
 
     /* set the matching work_color */
     pwq->work_color = wq->work_color;
 
     /* sync max_active to the current setting */
     pwq_adjust_max_active(pwq);
 
     /* link in @pwq */
     list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
 }
 
 /* obtain a pool matching @attr and create a pwq associating the pool and @wq */
 static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
                     const struct workqueue_attrs *attrs)
 {
     struct worker_pool *pool;
     struct pool_workqueue *pwq;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     pool = get_unbound_pool(attrs);
     if (!pool)
         return NULL;
 
     pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
     if (!pwq) {
         put_unbound_pool(pool);
         return NULL;
     }
 
     init_pwq(pwq, wq, pool);
     return pwq;
 }
 
 /**
  * wq_calc_node_cpumask - calculate a wq_attrs' cpumask for the specified node
  * @attrs: the wq_attrs of the default pwq of the target workqueue
  * @node: the target NUMA node
  * @cpu_going_down: if >= 0, the CPU to consider as offline
  * @cpumask: outarg, the resulting cpumask
  *
  * Calculate the cpumask a workqueue with @attrs should use on @node.  If
  * @cpu_going_down is >= 0, that cpu is considered offline during
  * calculation.  The result is stored in @cpumask.
  *
  * If NUMA affinity is not enabled, @attrs->cpumask is always used.  If
  * enabled and @node has online CPUs requested by @attrs, the returned
  * cpumask is the intersection of the possible CPUs of @node and
  * @attrs->cpumask.
  *
  * The caller is responsible for ensuring that the cpumask of @node stays
  * stable.
  *
  * Return: %true if the resulting @cpumask is different from @attrs->cpumask,
  * %false if equal.
  */
 static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
                  int cpu_going_down, cpumask_t *cpumask)
 {
     if (!wq_numa_enabled || attrs->no_numa)
         goto use_dfl;
 
     /* does @node have any online CPUs @attrs wants? */
     cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
     if (cpu_going_down >= 0)
         cpumask_clear_cpu(cpu_going_down, cpumask);
 
     if (cpumask_empty(cpumask))
         goto use_dfl;
 
     /* yeap, return possible CPUs in @node that @attrs wants */
     cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
 
     if (cpumask_empty(cpumask)) {
         pr_warn_once("WARNING: workqueue cpumask: online intersect > "
                 "possible intersect\n");
         return false;
     }
 
     return !cpumask_equal(cpumask, attrs->cpumask);
 
 use_dfl:
     cpumask_copy(cpumask, attrs->cpumask);
     return false;
 }
 
 /* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
 static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
                            int node,
                            struct pool_workqueue *pwq)
 {
     struct pool_workqueue *old_pwq;
 
     lockdep_assert_held(&wq_pool_mutex);
     lockdep_assert_held(&wq->mutex);
 
     /* link_pwq() can handle duplicate calls */
     link_pwq(pwq);
 
     old_pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
     rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
     return old_pwq;
 }
 
 /* context to store the prepared attrs & pwqs before applying */
 struct apply_wqattrs_ctx {
     struct workqueue_struct *wq;        /* target workqueue */
     struct workqueue_attrs  *attrs;     /* attrs to apply */
     struct list_head    list;       /* queued for batching commit */
     struct pool_workqueue   *dfl_pwq;
     struct pool_workqueue   *pwq_tbl[];
 };
 
 /* free the resources after success or abort */
 static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
 {
     if (ctx) {
         int node;
 
         for_each_node(node)
             put_pwq_unlocked(ctx->pwq_tbl[node]);
         put_pwq_unlocked(ctx->dfl_pwq);
 
         free_workqueue_attrs(ctx->attrs);
 
         kfree(ctx);
     }
 }
 
 /* allocate the attrs and pwqs for later installation */
 static struct apply_wqattrs_ctx *
 apply_wqattrs_prepare(struct workqueue_struct *wq,
               const struct workqueue_attrs *attrs)
 {
     struct apply_wqattrs_ctx *ctx;
     struct workqueue_attrs *new_attrs, *tmp_attrs;
     int node;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     ctx = kzalloc(struct_size(ctx, pwq_tbl, nr_node_ids), GFP_KERNEL);
 
     new_attrs = alloc_workqueue_attrs();
     tmp_attrs = alloc_workqueue_attrs();
     if (!ctx || !new_attrs || !tmp_attrs)
         goto out_free;
 
     /*
      * Calculate the attrs of the default pwq.
      * If the user configured cpumask doesn't overlap with the
      * wq_unbound_cpumask, we fallback to the wq_unbound_cpumask.
      */
     copy_workqueue_attrs(new_attrs, attrs);
     cpumask_and(new_attrs->cpumask, new_attrs->cpumask, wq_unbound_cpumask);
     if (unlikely(cpumask_empty(new_attrs->cpumask)))
         cpumask_copy(new_attrs->cpumask, wq_unbound_cpumask);
 
     /*
      * We may create multiple pwqs with differing cpumasks.  Make a
      * copy of @new_attrs which will be modified and used to obtain
      * pools.
      */
     copy_workqueue_attrs(tmp_attrs, new_attrs);
 
     /*
      * If something goes wrong during CPU up/down, we'll fall back to
      * the default pwq covering whole @attrs->cpumask.  Always create
      * it even if we don't use it immediately.
      */
     ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
     if (!ctx->dfl_pwq)
         goto out_free;
 
     for_each_node(node) {
         if (wq_calc_node_cpumask(new_attrs, node, -1, tmp_attrs->cpumask)) {
             ctx->pwq_tbl[node] = alloc_unbound_pwq(wq, tmp_attrs);
             if (!ctx->pwq_tbl[node])
                 goto out_free;
         } else {
             ctx->dfl_pwq->refcnt++;
             ctx->pwq_tbl[node] = ctx->dfl_pwq;
         }
     }
 
     /* save the user configured attrs and sanitize it. */
     copy_workqueue_attrs(new_attrs, attrs);
     cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
     ctx->attrs = new_attrs;
 
     ctx->wq = wq;
     free_workqueue_attrs(tmp_attrs);
     return ctx;
 
 out_free:
     free_workqueue_attrs(tmp_attrs);
     free_workqueue_attrs(new_attrs);
     apply_wqattrs_cleanup(ctx);
     return NULL;
 }
 
 /* set attrs and install prepared pwqs, @ctx points to old pwqs on return */
 static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 {
     int node;
 
     /* all pwqs have been created successfully, let's install'em */
     mutex_lock(&ctx->wq->mutex);
 
     copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs);
 
     /* save the previous pwq and install the new one */
     for_each_node(node)
         ctx->pwq_tbl[node] = numa_pwq_tbl_install(ctx->wq, node,
                               ctx->pwq_tbl[node]);
 
     /* @dfl_pwq might not have been used, ensure it's linked */
     link_pwq(ctx->dfl_pwq);
     swap(ctx->wq->dfl_pwq, ctx->dfl_pwq);
 
     mutex_unlock(&ctx->wq->mutex);
 }
 
 static void apply_wqattrs_lock(void)
 {
     /* CPUs should stay stable across pwq creations and installations */
     cpus_read_lock();
     mutex_lock(&wq_pool_mutex);
 }
 
 static void apply_wqattrs_unlock(void)
 {
     mutex_unlock(&wq_pool_mutex);
     cpus_read_unlock();
 }
 
 static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
                     const struct workqueue_attrs *attrs)
 {
     struct apply_wqattrs_ctx *ctx;
 
     /* only unbound workqueues can change attributes */
     if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
         return -EINVAL;
 
     /* creating multiple pwqs breaks ordering guarantee */
     if (!list_empty(&wq->pwqs)) {
         if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
             return -EINVAL;
 
         wq->flags &= ~__WQ_ORDERED;
     }
 
     ctx = apply_wqattrs_prepare(wq, attrs);
     if (!ctx)
         return -ENOMEM;
 
     /* the ctx has been prepared successfully, let's commit it */
     apply_wqattrs_commit(ctx);
     apply_wqattrs_cleanup(ctx);
 
     return 0;
 }
 
 /**
  * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
  * @wq: the target workqueue
  * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
  *
  * Apply @attrs to an unbound workqueue @wq.  Unless disabled, on NUMA
  * machines, this function maps a separate pwq to each NUMA node with
  * possibles CPUs in @attrs->cpumask so that work items are affine to the
  * NUMA node it was issued on.  Older pwqs are released as in-flight work
  * items finish.  Note that a work item which repeatedly requeues itself
  * back-to-back will stay on its current pwq.
  *
  * Performs GFP_KERNEL allocations.
  *
  * Assumes caller has CPU hotplug read exclusion, i.e. cpus_read_lock().
  *
  * Return: 0 on success and -errno on failure.
  */
 int apply_workqueue_attrs(struct workqueue_struct *wq,
               const struct workqueue_attrs *attrs)
 {
     int ret;
 
     lockdep_assert_cpus_held();
 
     mutex_lock(&wq_pool_mutex);
     ret = apply_workqueue_attrs_locked(wq, attrs);
     mutex_unlock(&wq_pool_mutex);
 
     return ret;
 }
 
 /**
  * wq_update_unbound_numa - update NUMA affinity of a wq for CPU hot[un]plug
  * @wq: the target workqueue
  * @cpu: the CPU coming up or going down
  * @online: whether @cpu is coming up or going down
  *
  * This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
  * %CPU_DOWN_FAILED.  @cpu is being hot[un]plugged, update NUMA affinity of
  * @wq accordingly.
  *
  * If NUMA affinity can't be adjusted due to memory allocation failure, it
  * falls back to @wq->dfl_pwq which may not be optimal but is always
  * correct.
  *
  * Note that when the last allowed CPU of a NUMA node goes offline for a
  * workqueue with a cpumask spanning multiple nodes, the workers which were
  * already executing the work items for the workqueue will lose their CPU
  * affinity and may execute on any CPU.  This is similar to how per-cpu
  * workqueues behave on CPU_DOWN.  If a workqueue user wants strict
  * affinity, it's the user's responsibility to flush the work item from
  * CPU_DOWN_PREPARE.
  */
 static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
                    bool online)
 {
     int node = cpu_to_node(cpu);
     int cpu_off = online ? -1 : cpu;
     struct pool_workqueue *old_pwq = NULL, *pwq;
     struct workqueue_attrs *target_attrs;
     cpumask_t *cpumask;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     if (!wq_numa_enabled || !(wq->flags & WQ_UNBOUND) ||
         wq->unbound_attrs->no_numa)
         return;
 
     /*
      * We don't wanna alloc/free wq_attrs for each wq for each CPU.
      * Let's use a preallocated one.  The following buf is protected by
      * CPU hotplug exclusion.
      */
     target_attrs = wq_update_unbound_numa_attrs_buf;
     cpumask = target_attrs->cpumask;
 
     copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
     pwq = unbound_pwq_by_node(wq, node);
 
     /*
      * Let's determine what needs to be done.  If the target cpumask is
      * different from the default pwq's, we need to compare it to @pwq's
      * and create a new one if they don't match.  If the target cpumask
      * equals the default pwq's, the default pwq should be used.
      */
     if (wq_calc_node_cpumask(wq->dfl_pwq->pool->attrs, node, cpu_off, cpumask)) {
         if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
             return;
     } else {
         goto use_dfl_pwq;
     }
 
     /* create a new pwq */
     pwq = alloc_unbound_pwq(wq, target_attrs);
     if (!pwq) {
         pr_warn("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
             wq->name);
         goto use_dfl_pwq;
     }
 
     /* Install the new pwq. */
     mutex_lock(&wq->mutex);
     old_pwq = numa_pwq_tbl_install(wq, node, pwq);
     goto out_unlock;
 
 use_dfl_pwq:
     mutex_lock(&wq->mutex);
     raw_spin_lock_irq(&wq->dfl_pwq->pool->lock);
     get_pwq(wq->dfl_pwq);
     raw_spin_unlock_irq(&wq->dfl_pwq->pool->lock);
     old_pwq = numa_pwq_tbl_install(wq, node, wq->dfl_pwq);
 out_unlock:
     mutex_unlock(&wq->mutex);
     put_pwq_unlocked(old_pwq);
 }
 
 static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 {
     bool highpri = wq->flags & WQ_HIGHPRI;
     int cpu, ret;
 
     if (!(wq->flags & WQ_UNBOUND)) {
         wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
         if (!wq->cpu_pwqs)
             return -ENOMEM;
 
         for_each_possible_cpu(cpu) {
             struct pool_workqueue *pwq =
                 per_cpu_ptr(wq->cpu_pwqs, cpu);
             struct worker_pool *cpu_pools =
                 per_cpu(cpu_worker_pools, cpu);
 
             init_pwq(pwq, wq, &cpu_pools[highpri]);
 
             mutex_lock(&wq->mutex);
             link_pwq(pwq);
             mutex_unlock(&wq->mutex);
         }
         return 0;
     }
 
     cpus_read_lock();
     if (wq->flags & __WQ_ORDERED) {
         ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
         /* there should only be single pwq for ordering guarantee */
         WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
                   wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
              "ordering guarantee broken for workqueue %s\n", wq->name);
     } else {
         ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
     }
     cpus_read_unlock();
 
     return ret;
 }
 
 static int wq_clamp_max_active(int max_active, unsigned int flags,
                    const char *name)
 {
     int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
 
     if (max_active < 1 || max_active > lim)
         pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
             max_active, name, 1, lim);
 
     return clamp_val(max_active, 1, lim);
 }
 
 /*
  * Workqueues which may be used during memory reclaim should have a rescuer
  * to guarantee forward progress.
  */
 static int init_rescuer(struct workqueue_struct *wq)
 {
     struct worker *rescuer;
     int ret;
 
     if (!(wq->flags & WQ_MEM_RECLAIM))
         return 0;
 
     rescuer = alloc_worker(NUMA_NO_NODE);
     if (!rescuer)
         return -ENOMEM;
 
     rescuer->rescue_wq = wq;
     rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", wq->name);
     if (IS_ERR(rescuer->task)) {
         ret = PTR_ERR(rescuer->task);
         kfree(rescuer);
         return ret;
     }
 
     wq->rescuer = rescuer;
     kthread_bind_mask(rescuer->task, cpu_possible_mask);
     wake_up_process(rescuer->task);
 
     return 0;
 }
 
 __printf(1, 4)
 struct workqueue_struct *alloc_workqueue(const char *fmt,
                      unsigned int flags,
                      int max_active, ...)
 {
     size_t tbl_size = 0;
     va_list args;
     struct workqueue_struct *wq;
     struct pool_workqueue *pwq;
 
     /*
      * Unbound && max_active == 1 used to imply ordered, which is no
      * longer the case on NUMA machines due to per-node pools.  While
      * alloc_ordered_workqueue() is the right way to create an ordered
      * workqueue, keep the previous behavior to avoid subtle breakages
      * on NUMA.
      */
     if ((flags & WQ_UNBOUND) && max_active == 1)
         flags |= __WQ_ORDERED;
 
     /* see the comment above the definition of WQ_POWER_EFFICIENT */
     if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
         flags |= WQ_UNBOUND;
 
     /* allocate wq and format name */
     if (flags & WQ_UNBOUND)
         tbl_size = nr_node_ids * sizeof(wq->numa_pwq_tbl[0]);
 
     wq = kzalloc(sizeof(*wq) + tbl_size, GFP_KERNEL);
     if (!wq)
         return NULL;
 
     if (flags & WQ_UNBOUND) {
         wq->unbound_attrs = alloc_workqueue_attrs();
         if (!wq->unbound_attrs)
             goto err_free_wq;
     }
 
     va_start(args, max_active);
     vsnprintf(wq->name, sizeof(wq->name), fmt, args);
     va_end(args);
 
     max_active = max_active ?: WQ_DFL_ACTIVE;
     max_active = wq_clamp_max_active(max_active, flags, wq->name);
 
     /* init wq */
     wq->flags = flags;
     wq->saved_max_active = max_active;
     mutex_init(&wq->mutex);
     atomic_set(&wq->nr_pwqs_to_flush, 0);
     INIT_LIST_HEAD(&wq->pwqs);
     INIT_LIST_HEAD(&wq->flusher_queue);
     INIT_LIST_HEAD(&wq->flusher_overflow);
     INIT_LIST_HEAD(&wq->maydays);
 
     wq_init_lockdep(wq);
     INIT_LIST_HEAD(&wq->list);
 
     if (alloc_and_link_pwqs(wq) < 0)
         goto err_unreg_lockdep;
 
     if (wq_online && init_rescuer(wq) < 0)
         goto err_destroy;
 
     if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
         goto err_destroy;
 
     /*
      * wq_pool_mutex protects global freeze state and workqueues list.
      * Grab it, adjust max_active and add the new @wq to workqueues
      * list.
      */
     mutex_lock(&wq_pool_mutex);
 
     mutex_lock(&wq->mutex);
     for_each_pwq(pwq, wq)
         pwq_adjust_max_active(pwq);
     mutex_unlock(&wq->mutex);
 
     list_add_tail_rcu(&wq->list, &workqueues);
 
     mutex_unlock(&wq_pool_mutex);
 
     return wq;
 
 err_unreg_lockdep:
     wq_unregister_lockdep(wq);
     wq_free_lockdep(wq);
 err_free_wq:
     free_workqueue_attrs(wq->unbound_attrs);
     kfree(wq);
     return NULL;
 err_destroy:
     destroy_workqueue(wq);
     return NULL;
 }
 EXPORT_SYMBOL_GPL(alloc_workqueue);
 
 static bool pwq_busy(struct pool_workqueue *pwq)
 {
     int i;
 
     for (i = 0; i < WORK_NR_COLORS; i++)
         if (pwq->nr_in_flight[i])
             return true;
 
     if ((pwq != pwq->wq->dfl_pwq) && (pwq->refcnt > 1))
         return true;
     if (pwq->nr_active || !list_empty(&pwq->inactive_works))
         return true;
 
     return false;
 }
 
 /**
  * destroy_workqueue - safely terminate a workqueue
  * @wq: target workqueue
  *
  * Safely destroy a workqueue. All work currently pending will be done first.
  */
 void destroy_workqueue(struct workqueue_struct *wq)
 {
     struct pool_workqueue *pwq;
     int node;
 
     /*
      * Remove it from sysfs first so that sanity check failure doesn't
      * lead to sysfs name conflicts.
      */
     workqueue_sysfs_unregister(wq);
 
     /* drain it before proceeding with destruction */
     drain_workqueue(wq);
 
     /* kill rescuer, if sanity checks fail, leave it w/o rescuer */
     if (wq->rescuer) {
         struct worker *rescuer = wq->rescuer;
 
         /* this prevents new queueing */
         raw_spin_lock_irq(&wq_mayday_lock);
         wq->rescuer = NULL;
         raw_spin_unlock_irq(&wq_mayday_lock);
 
         /* rescuer will empty maydays list before exiting */
         kthread_stop(rescuer->task);
         kfree(rescuer);
     }
 
     /*
      * Sanity checks - grab all the locks so that we wait for all
      * in-flight operations which may do put_pwq().
      */
     mutex_lock(&wq_pool_mutex);
     mutex_lock(&wq->mutex);
     for_each_pwq(pwq, wq) {
         raw_spin_lock_irq(&pwq->pool->lock);
         if (WARN_ON(pwq_busy(pwq))) {
             pr_warn("%s: %s has the following busy pwq\n",
                 __func__, wq->name);
             show_pwq(pwq);
             raw_spin_unlock_irq(&pwq->pool->lock);
             mutex_unlock(&wq->mutex);
             mutex_unlock(&wq_pool_mutex);
             show_one_workqueue(wq);
             return;
         }
         raw_spin_unlock_irq(&pwq->pool->lock);
     }
     mutex_unlock(&wq->mutex);
 
     /*
      * wq list is used to freeze wq, remove from list after
      * flushing is complete in case freeze races us.
      */
     list_del_rcu(&wq->list);
     mutex_unlock(&wq_pool_mutex);
 
     if (!(wq->flags & WQ_UNBOUND)) {
         wq_unregister_lockdep(wq);
         /*
          * The base ref is never dropped on per-cpu pwqs.  Directly
          * schedule RCU free.
          */
         call_rcu(&wq->rcu, rcu_free_wq);
     } else {
         /*
          * We're the sole accessor of @wq at this point.  Directly
          * access numa_pwq_tbl[] and dfl_pwq to put the base refs.
          * @wq will be freed when the last pwq is released.
          */
         for_each_node(node) {
             pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
             RCU_INIT_POINTER(wq->numa_pwq_tbl[node], NULL);
             put_pwq_unlocked(pwq);
         }
 
         /*
          * Put dfl_pwq.  @wq may be freed any time after dfl_pwq is
          * put.  Don't access it afterwards.
          */
         pwq = wq->dfl_pwq;
         wq->dfl_pwq = NULL;
         put_pwq_unlocked(pwq);
     }
 }
 EXPORT_SYMBOL_GPL(destroy_workqueue);
 
 /**
  * workqueue_set_max_active - adjust max_active of a workqueue
  * @wq: target workqueue
  * @max_active: new max_active value.
  *
  * Set max_active of @wq to @max_active.
  *
  * CONTEXT:
  * Don't call from IRQ context.
  */
 void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 {
     struct pool_workqueue *pwq;
 
     /* disallow meddling with max_active for ordered workqueues */
     if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
         return;
 
     max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
 
     mutex_lock(&wq->mutex);
 
     wq->flags &= ~__WQ_ORDERED;
     wq->saved_max_active = max_active;
 
     for_each_pwq(pwq, wq)
         pwq_adjust_max_active(pwq);
 
     mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL_GPL(workqueue_set_max_active);
 
 /**
  * current_work - retrieve %current task's work struct
  *
  * Determine if %current task is a workqueue worker and what it's working on.
  * Useful to find out the context that the %current task is running in.
  *
  * Return: work struct if %current task is a workqueue worker, %NULL otherwise.
  */
 struct work_struct *current_work(void)
 {
     struct worker *worker = current_wq_worker();
 
     return worker ? worker->current_work : NULL;
 }
 EXPORT_SYMBOL(current_work);
 
 /**
  * current_is_workqueue_rescuer - is %current workqueue rescuer?
  *
  * Determine whether %current is a workqueue rescuer.  Can be used from
  * work functions to determine whether it's being run off the rescuer task.
  *
  * Return: %true if %current is a workqueue rescuer. %false otherwise.
  */
 bool current_is_workqueue_rescuer(void)
 {
     struct worker *worker = current_wq_worker();
 
     return worker && worker->rescue_wq;
 }
 
 /**
  * workqueue_congested - test whether a workqueue is congested
  * @cpu: CPU in question
  * @wq: target workqueue
  *
  * Test whether @wq's cpu workqueue for @cpu is congested.  There is
  * no synchronization around this function and the test result is
  * unreliable and only useful as advisory hints or for debugging.
  *
  * If @cpu is WORK_CPU_UNBOUND, the test is performed on the local CPU.
  * Note that both per-cpu and unbound workqueues may be associated with
  * multiple pool_workqueues which have separate congested states.  A
  * workqueue being congested on one CPU doesn't mean the workqueue is also
  * contested on other CPUs / NUMA nodes.
  *
  * Return:
  * %true if congested, %false otherwise.
  */
 bool workqueue_congested(int cpu, struct workqueue_struct *wq)
 {
     struct pool_workqueue *pwq;
     bool ret;
 
     rcu_read_lock();
     preempt_disable();
 
     if (cpu == WORK_CPU_UNBOUND)
         cpu = smp_processor_id();
 
     if (!(wq->flags & WQ_UNBOUND))
         pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
     else
         pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
 
     ret = !list_empty(&pwq->inactive_works);
     preempt_enable();
     rcu_read_unlock();
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(workqueue_congested);
 
 /**
  * work_busy - test whether a work is currently pending or running
  * @work: the work to be tested
  *
  * Test whether @work is currently pending or running.  There is no
  * synchronization around this function and the test result is
  * unreliable and only useful as advisory hints or for debugging.
  *
  * Return:
  * OR'd bitmask of WORK_BUSY_* bits.
  */
 unsigned int work_busy(struct work_struct *work)
 {
     struct worker_pool *pool;
     unsigned long flags;
     unsigned int ret = 0;
 
     if (work_pending(work))
         ret |= WORK_BUSY_PENDING;
 
     rcu_read_lock();
     pool = get_work_pool(work);
     if (pool) {
         raw_spin_lock_irqsave(&pool->lock, flags);
         if (find_worker_executing_work(pool, work))
             ret |= WORK_BUSY_RUNNING;
         raw_spin_unlock_irqrestore(&pool->lock, flags);
     }
     rcu_read_unlock();
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(work_busy);
 
 /**
  * set_worker_desc - set description for the current work item
  * @fmt: printf-style format string
  * @...: arguments for the format string
  *
  * This function can be called by a running work function to describe what
  * the work item is about.  If the worker task gets dumped, this
  * information will be printed out together to help debugging.  The
  * description can be at most WORKER_DESC_LEN including the trailing '\0'.
  */
 void set_worker_desc(const char *fmt, ...)
 {
     struct worker *worker = current_wq_worker();
     va_list args;
 
     if (worker) {
         va_start(args, fmt);
         vsnprintf(worker->desc, sizeof(worker->desc), fmt, args);
         va_end(args);
     }
 }
 EXPORT_SYMBOL_GPL(set_worker_desc);
 
 /**
  * print_worker_info - print out worker information and description
  * @log_lvl: the log level to use when printing
  * @task: target task
  *
  * If @task is a worker and currently executing a work item, print out the
  * name of the workqueue being serviced and worker description set with
  * set_worker_desc() by the currently executing work item.
  *
  * This function can be safely called on any task as long as the
  * task_struct itself is accessible.  While safe, this function isn't
  * synchronized and may print out mixups or garbages of limited length.
  */
 void print_worker_info(const char *log_lvl, struct task_struct *task)
 {
     work_func_t *fn = NULL;
     char name[WQ_NAME_LEN] = { };
     char desc[WORKER_DESC_LEN] = { };
     struct pool_workqueue *pwq = NULL;
     struct workqueue_struct *wq = NULL;
     struct worker *worker;
 
     if (!(task->flags & PF_WQ_WORKER))
         return;
 
     /*
      * This function is called without any synchronization and @task
      * could be in any state.  Be careful with dereferences.
      */
     worker = kthread_probe_data(task);
 
     /*
      * Carefully copy the associated workqueue's workfn, name and desc.
      * Keep the original last '\0' in case the original is garbage.
      */
     copy_from_kernel_nofault(&fn, &worker->current_func, sizeof(fn));
     copy_from_kernel_nofault(&pwq, &worker->current_pwq, sizeof(pwq));
     copy_from_kernel_nofault(&wq, &pwq->wq, sizeof(wq));
     copy_from_kernel_nofault(name, wq->name, sizeof(name) - 1);
     copy_from_kernel_nofault(desc, worker->desc, sizeof(desc) - 1);
 
     if (fn || name[0] || desc[0]) {
         printk("%sWorkqueue: %s %ps", log_lvl, name, fn);
         if (strcmp(name, desc))
             pr_cont(" (%s)", desc);
         pr_cont("\n");
     }
 }
 
 static void pr_cont_pool_info(struct worker_pool *pool)
 {
     pr_cont(" cpus=%*pbl", nr_cpumask_bits, pool->attrs->cpumask);
     if (pool->node != NUMA_NO_NODE)
         pr_cont(" node=%d", pool->node);
     pr_cont(" flags=0x%x nice=%d", pool->flags, pool->attrs->nice);
 }
 
 static void pr_cont_work(bool comma, struct work_struct *work)
 {
     if (work->func == wq_barrier_func) {
         struct wq_barrier *barr;
 
         barr = container_of(work, struct wq_barrier, work);
 
         pr_cont("%s BAR(%d)", comma ? "," : "",
             task_pid_nr(barr->task));
     } else {
         pr_cont("%s %ps", comma ? "," : "", work->func);
     }
 }
 
 static void show_pwq(struct pool_workqueue *pwq)
 {
     struct worker_pool *pool = pwq->pool;
     struct work_struct *work;
     struct worker *worker;
     bool has_in_flight = false, has_pending = false;
     int bkt;
 
     pr_info("  pwq %d:", pool->id);
     pr_cont_pool_info(pool);
 
     pr_cont(" active=%d/%d refcnt=%d%s\n",
         pwq->nr_active, pwq->max_active, pwq->refcnt,
         !list_empty(&pwq->mayday_node) ? " MAYDAY" : "");
 
     hash_for_each(pool->busy_hash, bkt, worker, hentry) {
         if (worker->current_pwq == pwq) {
             has_in_flight = true;
             break;
         }
     }
     if (has_in_flight) {
         bool comma = false;
 
         pr_info("    in-flight:");
         hash_for_each(pool->busy_hash, bkt, worker, hentry) {
             if (worker->current_pwq != pwq)
                 continue;
 
             pr_cont("%s %d%s:%ps", comma ? "," : "",
                 task_pid_nr(worker->task),
                 worker->rescue_wq ? "(RESCUER)" : "",
                 worker->current_func);
             list_for_each_entry(work, &worker->scheduled, entry)
                 pr_cont_work(false, work);
             comma = true;
         }
         pr_cont("\n");
     }
 
     list_for_each_entry(work, &pool->worklist, entry) {
         if (get_work_pwq(work) == pwq) {
             has_pending = true;
             break;
         }
     }
     if (has_pending) {
         bool comma = false;
 
         pr_info("    pending:");
         list_for_each_entry(work, &pool->worklist, entry) {
             if (get_work_pwq(work) != pwq)
                 continue;
 
             pr_cont_work(comma, work);
             comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
         }
         pr_cont("\n");
     }
 
     if (!list_empty(&pwq->inactive_works)) {
         bool comma = false;
 
         pr_info("    inactive:");
         list_for_each_entry(work, &pwq->inactive_works, entry) {
             pr_cont_work(comma, work);
             comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
         }
         pr_cont("\n");
     }
 }
 
 /**
  * show_one_workqueue - dump state of specified workqueue
  * @wq: workqueue whose state will be printed
  */
 void show_one_workqueue(struct workqueue_struct *wq)
 {
     struct pool_workqueue *pwq;
     bool idle = true;
     unsigned long flags;
 
     for_each_pwq(pwq, wq) {
         if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
             idle = false;
             break;
         }
     }
     if (idle) /* Nothing to print for idle workqueue */
         return;
 
     pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
 
     for_each_pwq(pwq, wq) {
         raw_spin_lock_irqsave(&pwq->pool->lock, flags);
         if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
             /*
              * Defer printing to avoid deadlocks in console
              * drivers that queue work while holding locks
              * also taken in their write paths.
              */
             printk_deferred_enter();
             show_pwq(pwq);
             printk_deferred_exit();
         }
         raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
         /*
          * We could be printing a lot from atomic context, e.g.
          * sysrq-t -> show_all_workqueues(). Avoid triggering
          * hard lockup.
          */
         touch_nmi_watchdog();
     }
 
 }
 
 /**
  * show_one_worker_pool - dump state of specified worker pool
  * @pool: worker pool whose state will be printed
  */
 static void show_one_worker_pool(struct worker_pool *pool)
 {
     struct worker *worker;
     bool first = true;
     unsigned long flags;
 
     raw_spin_lock_irqsave(&pool->lock, flags);
     if (pool->nr_workers == pool->nr_idle)
         goto next_pool;
     /*
      * Defer printing to avoid deadlocks in console drivers that
      * queue work while holding locks also taken in their write
      * paths.
      */
     printk_deferred_enter();
     pr_info("pool %d:", pool->id);
     pr_cont_pool_info(pool);
     pr_cont(" hung=%us workers=%d",
         jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
         pool->nr_workers);
     if (pool->manager)
         pr_cont(" manager: %d",
             task_pid_nr(pool->manager->task));
     list_for_each_entry(worker, &pool->idle_list, entry) {
         pr_cont(" %s%d", first ? "idle: " : "",
             task_pid_nr(worker->task));
         first = false;
     }
     pr_cont("\n");
     printk_deferred_exit();
 next_pool:
     raw_spin_unlock_irqrestore(&pool->lock, flags);
     /*
      * We could be printing a lot from atomic context, e.g.
      * sysrq-t -> show_all_workqueues(). Avoid triggering
      * hard lockup.
      */
     touch_nmi_watchdog();
 
 }
 
 /**
  * show_all_workqueues - dump workqueue state
  *
  * Called from a sysrq handler or try_to_freeze_tasks() and prints out
  * all busy workqueues and pools.
  */
 void show_all_workqueues(void)
 {
     struct workqueue_struct *wq;
     struct worker_pool *pool;
     int pi;
 
     rcu_read_lock();
 
     pr_info("Showing busy workqueues and worker pools:\n");
 
     list_for_each_entry_rcu(wq, &workqueues, list)
         show_one_workqueue(wq);
 
     for_each_pool(pool, pi)
         show_one_worker_pool(pool);
 
     rcu_read_unlock();
 }
 
 /* used to show worker information through /proc/PID/{comm,stat,status} */
 void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
 {
     int off;
 
     /* always show the actual comm */
     off = strscpy(buf, task->comm, size);
     if (off < 0)
         return;
 
     /* stabilize PF_WQ_WORKER and worker pool association */
     mutex_lock(&wq_pool_attach_mutex);
 
     if (task->flags & PF_WQ_WORKER) {
         struct worker *worker = kthread_data(task);
         struct worker_pool *pool = worker->pool;
 
         if (pool) {
             raw_spin_lock_irq(&pool->lock);
             /*
              * ->desc tracks information (wq name or
              * set_worker_desc()) for the latest execution.  If
              * current, prepend '+', otherwise '-'.
              */
             if (worker->desc[0] != '\0') {
                 if (worker->current_work)
                     scnprintf(buf + off, size - off, "+%s",
                           worker->desc);
                 else
                     scnprintf(buf + off, size - off, "-%s",
                           worker->desc);
             }
             raw_spin_unlock_irq(&pool->lock);
         }
     }
 
     mutex_unlock(&wq_pool_attach_mutex);
 }
 
 #ifdef CONFIG_SMP
 
 /*
  * CPU hotplug.
  *
  * There are two challenges in supporting CPU hotplug.  Firstly, there
  * are a lot of assumptions on strong associations among work, pwq and
  * pool which make migrating pending and scheduled works very
  * difficult to implement without impacting hot paths.  Secondly,
  * worker pools serve mix of short, long and very long running works making
  * blocked draining impractical.
  *
  * This is solved by allowing the pools to be disassociated from the CPU
  * running as an unbound one and allowing it to be reattached later if the
  * cpu comes back online.
  */
 
 static void unbind_workers(int cpu)
 {
     struct worker_pool *pool;
     struct worker *worker;
 
     for_each_cpu_worker_pool(pool, cpu) {
         mutex_lock(&wq_pool_attach_mutex);
         raw_spin_lock_irq(&pool->lock);
 
         /*
          * We've blocked all attach/detach operations. Make all workers
          * unbound and set DISASSOCIATED.  Before this, all workers
          * must be on the cpu.  After this, they may become diasporas.
          * And the preemption disabled section in their sched callbacks
          * are guaranteed to see WORKER_UNBOUND since the code here
          * is on the same cpu.
          */
         for_each_pool_worker(worker, pool)
             worker->flags |= WORKER_UNBOUND;
 
         pool->flags |= POOL_DISASSOCIATED;
 
         /*
          * The handling of nr_running in sched callbacks are disabled
          * now.  Zap nr_running.  After this, nr_running stays zero and
          * need_more_worker() and keep_working() are always true as
          * long as the worklist is not empty.  This pool now behaves as
          * an unbound (in terms of concurrency management) pool which
          * are served by workers tied to the pool.
          */
         pool->nr_running = 0;
 
         /*
          * With concurrency management just turned off, a busy
          * worker blocking could lead to lengthy stalls.  Kick off
          * unbound chain execution of currently pending work items.
          */
         wake_up_worker(pool);
 
         raw_spin_unlock_irq(&pool->lock);
 
         for_each_pool_worker(worker, pool) {
             kthread_set_per_cpu(worker->task, -1);
             if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
             else
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
         }
 
         mutex_unlock(&wq_pool_attach_mutex);
     }
 }
 
 /**
  * rebind_workers - rebind all workers of a pool to the associated CPU
  * @pool: pool of interest
  *
  * @pool->cpu is coming online.  Rebind all workers to the CPU.
  */
 static void rebind_workers(struct worker_pool *pool)
 {
     struct worker *worker;
 
     lockdep_assert_held(&wq_pool_attach_mutex);
 
     /*
      * Restore CPU affinity of all workers.  As all idle workers should
      * be on the run-queue of the associated CPU before any local
      * wake-ups for concurrency management happen, restore CPU affinity
      * of all workers first and then clear UNBOUND.  As we're called
      * from CPU_ONLINE, the following shouldn't fail.
      */
     for_each_pool_worker(worker, pool) {
         kthread_set_per_cpu(worker->task, pool->cpu);
         WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
                           pool->attrs->cpumask) < 0);
     }
 
     raw_spin_lock_irq(&pool->lock);
 
     pool->flags &= ~POOL_DISASSOCIATED;
 
     for_each_pool_worker(worker, pool) {
         unsigned int worker_flags = worker->flags;
 
         /*
          * We want to clear UNBOUND but can't directly call
          * worker_clr_flags() or adjust nr_running.  Atomically
          * replace UNBOUND with another NOT_RUNNING flag REBOUND.
          * @worker will clear REBOUND using worker_clr_flags() when
          * it initiates the next execution cycle thus restoring
          * concurrency management.  Note that when or whether
          * @worker clears REBOUND doesn't affect correctness.
          *
          * WRITE_ONCE() is necessary because @worker->flags may be
          * tested without holding any lock in
          * wq_worker_running().  Without it, NOT_RUNNING test may
          * fail incorrectly leading to premature concurrency
          * management operations.
          */
         WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
         worker_flags |= WORKER_REBOUND;
         worker_flags &= ~WORKER_UNBOUND;
         WRITE_ONCE(worker->flags, worker_flags);
     }
 
     raw_spin_unlock_irq(&pool->lock);
 }
 
 /**
  * restore_unbound_workers_cpumask - restore cpumask of unbound workers
  * @pool: unbound pool of interest
  * @cpu: the CPU which is coming up
  *
  * An unbound pool may end up with a cpumask which doesn't have any online
  * CPUs.  When a worker of such pool get scheduled, the scheduler resets
  * its cpus_allowed.  If @cpu is in @pool's cpumask which didn't have any
  * online CPU before, cpus_allowed of all its workers should be restored.
  */
 static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
 {
     static cpumask_t cpumask;
     struct worker *worker;
 
     lockdep_assert_held(&wq_pool_attach_mutex);
 
     /* is @cpu allowed for @pool? */
     if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
         return;
 
     cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
 
     /* as we're called from CPU_ONLINE, the following shouldn't fail */
     for_each_pool_worker(worker, pool)
         WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, &cpumask) < 0);
 }
 
 int workqueue_prepare_cpu(unsigned int cpu)
 {
     struct worker_pool *pool;
 
     for_each_cpu_worker_pool(pool, cpu) {
         if (pool->nr_workers)
             continue;
         if (!create_worker(pool))
             return -ENOMEM;
     }
     return 0;
 }
 
 int workqueue_online_cpu(unsigned int cpu)
 {
     struct worker_pool *pool;
     struct workqueue_struct *wq;
     int pi;
 
     mutex_lock(&wq_pool_mutex);
 
     for_each_pool(pool, pi) {
         mutex_lock(&wq_pool_attach_mutex);
 
         if (pool->cpu == cpu)
             rebind_workers(pool);
         else if (pool->cpu < 0)
             restore_unbound_workers_cpumask(pool, cpu);
 
         mutex_unlock(&wq_pool_attach_mutex);
     }
 
     /* update NUMA affinity of unbound workqueues */
     list_for_each_entry(wq, &workqueues, list)
         wq_update_unbound_numa(wq, cpu, true);
 
     mutex_unlock(&wq_pool_mutex);
     return 0;
 }
 
 int workqueue_offline_cpu(unsigned int cpu)
 {
     struct workqueue_struct *wq;
 
     /* unbinding per-cpu workers should happen on the local CPU */
     if (WARN_ON(cpu != smp_processor_id()))
         return -1;
 
     unbind_workers(cpu);
 
     /* update NUMA affinity of unbound workqueues */
     mutex_lock(&wq_pool_mutex);
     list_for_each_entry(wq, &workqueues, list)
         wq_update_unbound_numa(wq, cpu, false);
     mutex_unlock(&wq_pool_mutex);
 
     return 0;
 }
 
 struct work_for_cpu {
     struct work_struct work;
     long (*fn)(void *);
     void *arg;
     long ret;
 };
 
 static void work_for_cpu_fn(struct work_struct *work)
 {
     struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
 
     wfc->ret = wfc->fn(wfc->arg);
 }
 
 /**
  * work_on_cpu - run a function in thread context on a particular cpu
  * @cpu: the cpu to run on
  * @fn: the function to run
  * @arg: the function arg
  *
  * It is up to the caller to ensure that the cpu doesn't go offline.
  * The caller must not hold any locks which would prevent @fn from completing.
  *
  * Return: The value @fn returns.
  */
 long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
 {
     struct work_for_cpu wfc = { .fn = fn, .arg = arg };
 
     INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
     schedule_work_on(cpu, &wfc.work);
     flush_work(&wfc.work);
     destroy_work_on_stack(&wfc.work);
     return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu);
 
 /**
  * work_on_cpu_safe - run a function in thread context on a particular cpu
  * @cpu: the cpu to run on
  * @fn:  the function to run
  * @arg: the function argument
  *
  * Disables CPU hotplug and calls work_on_cpu(). The caller must not hold
  * any locks which would prevent @fn from completing.
  *
  * Return: The value @fn returns.
  */
 long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
 {
     long ret = -ENODEV;
 
     cpus_read_lock();
     if (cpu_online(cpu))
         ret = work_on_cpu(cpu, fn, arg);
     cpus_read_unlock();
     return ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu_safe);
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_FREEZER
 
 /**
  * freeze_workqueues_begin - begin freezing workqueues
  *
  * Start freezing workqueues.  After this function returns, all freezable
  * workqueues will queue new works to their inactive_works list instead of
  * pool->worklist.
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void freeze_workqueues_begin(void)
 {
     struct workqueue_struct *wq;
     struct pool_workqueue *pwq;
 
     mutex_lock(&wq_pool_mutex);
 
     WARN_ON_ONCE(workqueue_freezing);
     workqueue_freezing = true;
 
     list_for_each_entry(wq, &workqueues, list) {
         mutex_lock(&wq->mutex);
         for_each_pwq(pwq, wq)
             pwq_adjust_max_active(pwq);
         mutex_unlock(&wq->mutex);
     }
 
     mutex_unlock(&wq_pool_mutex);
 }
 
 /**
  * freeze_workqueues_busy - are freezable workqueues still busy?
  *
  * Check whether freezing is complete.  This function must be called
  * between freeze_workqueues_begin() and thaw_workqueues().
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex.
  *
  * Return:
  * %true if some freezable workqueues are still busy.  %false if freezing
  * is complete.
  */
 bool freeze_workqueues_busy(void)
 {
     bool busy = false;
     struct workqueue_struct *wq;
     struct pool_workqueue *pwq;
 
     mutex_lock(&wq_pool_mutex);
 
     WARN_ON_ONCE(!workqueue_freezing);
 
     list_for_each_entry(wq, &workqueues, list) {
         if (!(wq->flags & WQ_FREEZABLE))
             continue;
         /*
          * nr_active is monotonically decreasing.  It's safe
          * to peek without lock.
          */
         rcu_read_lock();
         for_each_pwq(pwq, wq) {
             WARN_ON_ONCE(pwq->nr_active < 0);
             if (pwq->nr_active) {
                 busy = true;
                 rcu_read_unlock();
                 goto out_unlock;
             }
         }
         rcu_read_unlock();
     }
 out_unlock:
     mutex_unlock(&wq_pool_mutex);
     return busy;
 }
 
 /**
  * thaw_workqueues - thaw workqueues
  *
  * Thaw workqueues.  Normal queueing is restored and all collected
  * frozen works are transferred to their respective pool worklists.
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void thaw_workqueues(void)
 {
     struct workqueue_struct *wq;
     struct pool_workqueue *pwq;
 
     mutex_lock(&wq_pool_mutex);
 
     if (!workqueue_freezing)
         goto out_unlock;
 
     workqueue_freezing = false;
 
     /* restore max_active and repopulate worklist */
     list_for_each_entry(wq, &workqueues, list) {
         mutex_lock(&wq->mutex);
         for_each_pwq(pwq, wq)
             pwq_adjust_max_active(pwq);
         mutex_unlock(&wq->mutex);
     }
 
 out_unlock:
     mutex_unlock(&wq_pool_mutex);
 }
 #endif /* CONFIG_FREEZER */
 
 static int workqueue_apply_unbound_cpumask(void)
 {
     LIST_HEAD(ctxs);
     int ret = 0;
     struct workqueue_struct *wq;
     struct apply_wqattrs_ctx *ctx, *n;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     list_for_each_entry(wq, &workqueues, list) {
         if (!(wq->flags & WQ_UNBOUND))
             continue;
         /* creating multiple pwqs breaks ordering guarantee */
         if (wq->flags & __WQ_ORDERED)
             continue;
 
         ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs);
         if (!ctx) {
             ret = -ENOMEM;
             break;
         }
 
         list_add_tail(&ctx->list, &ctxs);
     }
 
     list_for_each_entry_safe(ctx, n, &ctxs, list) {
         if (!ret)
             apply_wqattrs_commit(ctx);
         apply_wqattrs_cleanup(ctx);
     }
 
     return ret;
 }
 
 /**
  *  workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
  *  @cpumask: the cpumask to set
  *
  *  The low-level workqueues cpumask is a global cpumask that limits
  *  the affinity of all unbound workqueues.  This function check the @cpumask
  *  and apply it to all unbound workqueues and updates all pwqs of them.
  *
  *  Return: 0   - Success
  *          -EINVAL - Invalid @cpumask
  *          -ENOMEM - Failed to allocate memory for attrs or pwqs.
  */
 int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 {
     int ret = -EINVAL;
     cpumask_var_t saved_cpumask;
 
     /*
      * Not excluding isolated cpus on purpose.
      * If the user wishes to include them, we allow that.
      */
     cpumask_and(cpumask, cpumask, cpu_possible_mask);
     if (!cpumask_empty(cpumask)) {
         apply_wqattrs_lock();
         if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
             ret = 0;
             goto out_unlock;
         }
 
         if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL)) {
             ret = -ENOMEM;
             goto out_unlock;
         }
 
         /* save the old wq_unbound_cpumask. */
         cpumask_copy(saved_cpumask, wq_unbound_cpumask);
 
         /* update wq_unbound_cpumask at first and apply it to wqs. */
         cpumask_copy(wq_unbound_cpumask, cpumask);
         ret = workqueue_apply_unbound_cpumask();
 
         /* restore the wq_unbound_cpumask when failed. */
         if (ret < 0)
             cpumask_copy(wq_unbound_cpumask, saved_cpumask);
 
         free_cpumask_var(saved_cpumask);
 out_unlock:
         apply_wqattrs_unlock();
     }
 
     return ret;
 }
 
 #ifdef CONFIG_SYSFS
 /*
  * Workqueues with WQ_SYSFS flag set is visible to userland via
  * /sys/bus/workqueue/devices/WQ_NAME.  All visible workqueues have the
  * following attributes.
  *
  *  per_cpu RO bool : whether the workqueue is per-cpu or unbound
  *  max_active  RW int  : maximum number of in-flight work items
  *
  * Unbound workqueues have the following extra attributes.
  *
  *  pool_ids    RO int  : the associated pool IDs for each node
  *  nice    RW int  : nice value of the workers
  *  cpumask RW mask : bitmask of allowed CPUs for the workers
  *  numa    RW bool : whether enable NUMA affinity
  */
 struct wq_device {
     struct workqueue_struct     *wq;
     struct device           dev;
 };
 
 static struct workqueue_struct *dev_to_wq(struct device *dev)
 {
     struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
 
     return wq_dev->wq;
 }
 
 static ssize_t per_cpu_show(struct device *dev, struct device_attribute *attr,
                 char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
 
     return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
 }
 static DEVICE_ATTR_RO(per_cpu);
 
 static ssize_t max_active_show(struct device *dev,
                    struct device_attribute *attr, char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
 
     return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
 }
 
 static ssize_t max_active_store(struct device *dev,
                 struct device_attribute *attr, const char *buf,
                 size_t count)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     int val;
 
     if (sscanf(buf, "%d", &val) != 1 || val <= 0)
         return -EINVAL;
 
     workqueue_set_max_active(wq, val);
     return count;
 }
 static DEVICE_ATTR_RW(max_active);
 
 static struct attribute *wq_sysfs_attrs[] = {
     &dev_attr_per_cpu.attr,
     &dev_attr_max_active.attr,
     NULL,
 };
 ATTRIBUTE_GROUPS(wq_sysfs);
 
 static ssize_t wq_pool_ids_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     const char *delim = "";
     int node, written = 0;
 
     cpus_read_lock();
     rcu_read_lock();
     for_each_node(node) {
         written += scnprintf(buf + written, PAGE_SIZE - written,
                      "%s%d:%d", delim, node,
                      unbound_pwq_by_node(wq, node)->pool->id);
         delim = " ";
     }
     written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
     rcu_read_unlock();
     cpus_read_unlock();
 
     return written;
 }
 
 static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
                 char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     int written;
 
     mutex_lock(&wq->mutex);
     written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
     mutex_unlock(&wq->mutex);
 
     return written;
 }
 
 /* prepare workqueue_attrs for sysfs store operations */
 static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
 {
     struct workqueue_attrs *attrs;
 
     lockdep_assert_held(&wq_pool_mutex);
 
     attrs = alloc_workqueue_attrs();
     if (!attrs)
         return NULL;
 
     copy_workqueue_attrs(attrs, wq->unbound_attrs);
     return attrs;
 }
 
 static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
                  const char *buf, size_t count)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     struct workqueue_attrs *attrs;
     int ret = -ENOMEM;
 
     apply_wqattrs_lock();
 
     attrs = wq_sysfs_prep_attrs(wq);
     if (!attrs)
         goto out_unlock;
 
     if (sscanf(buf, "%d", &attrs->nice) == 1 &&
         attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
         ret = apply_workqueue_attrs_locked(wq, attrs);
     else
         ret = -EINVAL;
 
 out_unlock:
     apply_wqattrs_unlock();
     free_workqueue_attrs(attrs);
     return ret ?: count;
 }
 
 static ssize_t wq_cpumask_show(struct device *dev,
                    struct device_attribute *attr, char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     int written;
 
     mutex_lock(&wq->mutex);
     written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
                 cpumask_pr_args(wq->unbound_attrs->cpumask));
     mutex_unlock(&wq->mutex);
     return written;
 }
 
 static ssize_t wq_cpumask_store(struct device *dev,
                 struct device_attribute *attr,
                 const char *buf, size_t count)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     struct workqueue_attrs *attrs;
     int ret = -ENOMEM;
 
     apply_wqattrs_lock();
 
     attrs = wq_sysfs_prep_attrs(wq);
     if (!attrs)
         goto out_unlock;
 
     ret = cpumask_parse(buf, attrs->cpumask);
     if (!ret)
         ret = apply_workqueue_attrs_locked(wq, attrs);
 
 out_unlock:
     apply_wqattrs_unlock();
     free_workqueue_attrs(attrs);
     return ret ?: count;
 }
 
 static ssize_t wq_numa_show(struct device *dev, struct device_attribute *attr,
                 char *buf)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     int written;
 
     mutex_lock(&wq->mutex);
     written = scnprintf(buf, PAGE_SIZE, "%d\n",
                 !wq->unbound_attrs->no_numa);
     mutex_unlock(&wq->mutex);
 
     return written;
 }
 
 static ssize_t wq_numa_store(struct device *dev, struct device_attribute *attr,
                  const char *buf, size_t count)
 {
     struct workqueue_struct *wq = dev_to_wq(dev);
     struct workqueue_attrs *attrs;
     int v, ret = -ENOMEM;
 
     apply_wqattrs_lock();
 
     attrs = wq_sysfs_prep_attrs(wq);
     if (!attrs)
         goto out_unlock;
 
     ret = -EINVAL;
     if (sscanf(buf, "%d", &v) == 1) {
         attrs->no_numa = !v;
         ret = apply_workqueue_attrs_locked(wq, attrs);
     }
 
 out_unlock:
     apply_wqattrs_unlock();
     free_workqueue_attrs(attrs);
     return ret ?: count;
 }
 
 static struct device_attribute wq_sysfs_unbound_attrs[] = {
     __ATTR(pool_ids, 0444, wq_pool_ids_show, NULL),
     __ATTR(nice, 0644, wq_nice_show, wq_nice_store),
     __ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
     __ATTR(numa, 0644, wq_numa_show, wq_numa_store),
     __ATTR_NULL,
 };
 
 static struct bus_type wq_subsys = {
     .name               = "workqueue",
     .dev_groups         = wq_sysfs_groups,
 };
 
 static ssize_t wq_unbound_cpumask_show(struct device *dev,
         struct device_attribute *attr, char *buf)
 {
     int written;
 
     mutex_lock(&wq_pool_mutex);
     written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
                 cpumask_pr_args(wq_unbound_cpumask));
     mutex_unlock(&wq_pool_mutex);
 
     return written;
 }
 
 static ssize_t wq_unbound_cpumask_store(struct device *dev,
         struct device_attribute *attr, const char *buf, size_t count)
 {
     cpumask_var_t cpumask;
     int ret;
 
     if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
         return -ENOMEM;
 
     ret = cpumask_parse(buf, cpumask);
     if (!ret)
         ret = workqueue_set_unbound_cpumask(cpumask);
 
     free_cpumask_var(cpumask);
     return ret ? ret : count;
 }
 
 static struct device_attribute wq_sysfs_cpumask_attr =
     __ATTR(cpumask, 0644, wq_unbound_cpumask_show,
            wq_unbound_cpumask_store);
 
 static int __init wq_sysfs_init(void)
 {
     int err;
 
     err = subsys_virtual_register(&wq_subsys, NULL);
     if (err)
         return err;
 
     return device_create_file(wq_subsys.dev_root, &wq_sysfs_cpumask_attr);
 }
 core_initcall(wq_sysfs_init);
 
 static void wq_device_release(struct device *dev)
 {
     struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
 
     kfree(wq_dev);
 }
 
 /**
  * workqueue_sysfs_register - make a workqueue visible in sysfs
  * @wq: the workqueue to register
  *
  * Expose @wq in sysfs under /sys/bus/workqueue/devices.
  * alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
  * which is the preferred method.
  *
  * Workqueue user should use this function directly iff it wants to apply
  * workqueue_attrs before making the workqueue visible in sysfs; otherwise,
  * apply_workqueue_attrs() may race against userland updating the
  * attributes.
  *
  * Return: 0 on success, -errno on failure.
  */
 int workqueue_sysfs_register(struct workqueue_struct *wq)
 {
     struct wq_device *wq_dev;
     int ret;
 
     /*
      * Adjusting max_active or creating new pwqs by applying
      * attributes breaks ordering guarantee.  Disallow exposing ordered
      * workqueues.
      */
     if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
         return -EINVAL;
 
     wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
     if (!wq_dev)
         return -ENOMEM;
 
     wq_dev->wq = wq;
     wq_dev->dev.bus = &wq_subsys;
     wq_dev->dev.release = wq_device_release;
     dev_set_name(&wq_dev->dev, "%s", wq->name);
 
     /*
      * unbound_attrs are created separately.  Suppress uevent until
      * everything is ready.
      */
     dev_set_uevent_suppress(&wq_dev->dev, true);
 
     ret = device_register(&wq_dev->dev);
     if (ret) {
         put_device(&wq_dev->dev);
         wq->wq_dev = NULL;
         return ret;
     }
 
     if (wq->flags & WQ_UNBOUND) {
         struct device_attribute *attr;
 
         for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
             ret = device_create_file(&wq_dev->dev, attr);
             if (ret) {
                 device_unregister(&wq_dev->dev);
                 wq->wq_dev = NULL;
                 return ret;
             }
         }
     }
 
     dev_set_uevent_suppress(&wq_dev->dev, false);
     kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
     return 0;
 }
 
 /**
  * workqueue_sysfs_unregister - undo workqueue_sysfs_register()
  * @wq: the workqueue to unregister
  *
  * If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
  */
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
 {
     struct wq_device *wq_dev = wq->wq_dev;
 
     if (!wq->wq_dev)
         return;
 
     wq->wq_dev = NULL;
     device_unregister(&wq_dev->dev);
 }
 #else   /* CONFIG_SYSFS */
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq) { }
 #endif  /* CONFIG_SYSFS */
 
 /*
  * Workqueue watchdog.
  *
  * Stall may be caused by various bugs - missing WQ_MEM_RECLAIM, illegal
  * flush dependency, a concurrency managed work item which stays RUNNING
  * indefinitely.  Workqueue stalls can be very difficult to debug as the
  * usual warning mechanisms don't trigger and internal workqueue state is
  * largely opaque.
  *
  * Workqueue watchdog monitors all worker pools periodically and dumps
  * state if some pools failed to make forward progress for a while where
  * forward progress is defined as the first item on ->worklist changing.
  *
  * This mechanism is controlled through the kernel parameter
  * "workqueue.watchdog_thresh" which can be updated at runtime through the
  * corresponding sysfs parameter file.
  */
 #ifdef CONFIG_WQ_WATCHDOG
 
 static unsigned long wq_watchdog_thresh = 30;
 static struct timer_list wq_watchdog_timer;
 
 static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
 static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;
 
 static void wq_watchdog_reset_touched(void)
 {
     int cpu;
 
     wq_watchdog_touched = jiffies;
     for_each_possible_cpu(cpu)
         per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
 }
 
 static void wq_watchdog_timer_fn(struct timer_list *unused)
 {
     unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
     bool lockup_detected = false;
     unsigned long now = jiffies;
     struct worker_pool *pool;
     int pi;
 
     if (!thresh)
         return;
 
     rcu_read_lock();
 
     for_each_pool(pool, pi) {
         unsigned long pool_ts, touched, ts;
 
         if (list_empty(&pool->worklist))
             continue;
 
         /*
          * If a virtual machine is stopped by the host it can look to
          * the watchdog like a stall.
          */
         kvm_check_and_clear_guest_paused();
 
         /* get the latest of pool and touched timestamps */
         if (pool->cpu >= 0)
             touched = READ_ONCE(per_cpu(wq_watchdog_touched_cpu, pool->cpu));
         else
             touched = READ_ONCE(wq_watchdog_touched);
         pool_ts = READ_ONCE(pool->watchdog_ts);
 
         if (time_after(pool_ts, touched))
             ts = pool_ts;
         else
             ts = touched;
 
         /* did we stall? */
         if (time_after(now, ts + thresh)) {
             lockup_detected = true;
             pr_emerg("BUG: workqueue lockup - pool");
             pr_cont_pool_info(pool);
             pr_cont(" stuck for %us!\n",
                 jiffies_to_msecs(now - pool_ts) / 1000);
         }
     }
 
     rcu_read_unlock();
 
     if (lockup_detected)
         show_all_workqueues();
 
     wq_watchdog_reset_touched();
     mod_timer(&wq_watchdog_timer, jiffies + thresh);
 }
 
 notrace void wq_watchdog_touch(int cpu)
 {
     if (cpu >= 0)
         per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
 
     wq_watchdog_touched = jiffies;
 }
 
 static void wq_watchdog_set_thresh(unsigned long thresh)
 {
     wq_watchdog_thresh = 0;
     del_timer_sync(&wq_watchdog_timer);
 
     if (thresh) {
         wq_watchdog_thresh = thresh;
         wq_watchdog_reset_touched();
         mod_timer(&wq_watchdog_timer, jiffies + thresh * HZ);
     }
 }
 
 static int wq_watchdog_param_set_thresh(const char *val,
                     const struct kernel_param *kp)
 {
     unsigned long thresh;
     int ret;
 
     ret = kstrtoul(val, 0, &thresh);
     if (ret)
         return ret;
 
     if (system_wq)
         wq_watchdog_set_thresh(thresh);
     else
         wq_watchdog_thresh = thresh;
 
     return 0;
 }
 
 static const struct kernel_param_ops wq_watchdog_thresh_ops = {
     .set    = wq_watchdog_param_set_thresh,
     .get    = param_get_ulong,
 };
 
 module_param_cb(watchdog_thresh, &wq_watchdog_thresh_ops, &wq_watchdog_thresh,
         0644);
 
 static void wq_watchdog_init(void)
 {
     timer_setup(&wq_watchdog_timer, wq_watchdog_timer_fn, TIMER_DEFERRABLE);
     wq_watchdog_set_thresh(wq_watchdog_thresh);
 }
 
 #else   /* CONFIG_WQ_WATCHDOG */
 
 static inline void wq_watchdog_init(void) { }
 
 #endif  /* CONFIG_WQ_WATCHDOG */
 
 static void __init wq_numa_init(void)
 {
     cpumask_var_t *tbl;
     int node, cpu;
 
     if (num_possible_nodes() <= 1)
         return;
 
     if (wq_disable_numa) {
         pr_info("workqueue: NUMA affinity support disabled\n");
         return;
     }
 
     for_each_possible_cpu(cpu) {
         if (WARN_ON(cpu_to_node(cpu) == NUMA_NO_NODE)) {
             pr_warn("workqueue: NUMA node mapping not available for cpu%d, disabling NUMA support\n", cpu);
             return;
         }
     }
 
     wq_update_unbound_numa_attrs_buf = alloc_workqueue_attrs();
     BUG_ON(!wq_update_unbound_numa_attrs_buf);
 
     /*
      * We want masks of possible CPUs of each node which isn't readily
      * available.  Build one from cpu_to_node() which should have been
      * fully initialized by now.
      */
     tbl = kcalloc(nr_node_ids, sizeof(tbl[0]), GFP_KERNEL);
     BUG_ON(!tbl);
 
     for_each_node(node)
         BUG_ON(!zalloc_cpumask_var_node(&tbl[node], GFP_KERNEL,
                 node_online(node) ? node : NUMA_NO_NODE));
 
     for_each_possible_cpu(cpu) {
         node = cpu_to_node(cpu);
         cpumask_set_cpu(cpu, tbl[node]);
     }
 
     wq_numa_possible_cpumask = tbl;
     wq_numa_enabled = true;
 }
 
 /**
  * workqueue_init_early - early init for workqueue subsystem
  *
  * This is the first half of two-staged workqueue subsystem initialization
  * and invoked as soon as the bare basics - memory allocation, cpumasks and
  * idr are up.  It sets up all the data structures and system workqueues
  * and allows early boot code to create workqueues and queue/cancel work
  * items.  Actual work item execution starts only after kthreads can be
  * created and scheduled right before early initcalls.
  */
 void __init workqueue_init_early(void)
 {
     int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
     int i, cpu;
 
     BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
 
     BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
     cpumask_copy(wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_WQ));
     cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_DOMAIN));
 
     pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);
 
     /* initialize CPU pools */
     for_each_possible_cpu(cpu) {
         struct worker_pool *pool;
 
         i = 0;
         for_each_cpu_worker_pool(pool, cpu) {
             BUG_ON(init_worker_pool(pool));
             pool->cpu = cpu;
             cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
             pool->attrs->nice = std_nice[i++];
             pool->node = cpu_to_node(cpu);
 
             /* alloc pool ID */
             mutex_lock(&wq_pool_mutex);
             BUG_ON(worker_pool_assign_id(pool));
             mutex_unlock(&wq_pool_mutex);
         }
     }
 
     /* create default unbound and ordered wq attrs */
     for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
         struct workqueue_attrs *attrs;
 
         BUG_ON(!(attrs = alloc_workqueue_attrs()));
         attrs->nice = std_nice[i];
         unbound_std_wq_attrs[i] = attrs;
 
         /*
          * An ordered wq should have only one pwq as ordering is
          * guaranteed by max_active which is enforced by pwqs.
          * Turn off NUMA so that dfl_pwq is used for all nodes.
          */
         BUG_ON(!(attrs = alloc_workqueue_attrs()));
         attrs->nice = std_nice[i];
         attrs->no_numa = true;
         ordered_wq_attrs[i] = attrs;
     }
 
     system_wq = alloc_workqueue("events", 0, 0);
     system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
     system_long_wq = alloc_workqueue("events_long", 0, 0);
     system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
                         WQ_UNBOUND_MAX_ACTIVE);
     system_freezable_wq = alloc_workqueue("events_freezable",
                           WQ_FREEZABLE, 0);
     system_power_efficient_wq = alloc_workqueue("events_power_efficient",
                           WQ_POWER_EFFICIENT, 0);
     system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_power_efficient",
                           WQ_FREEZABLE | WQ_POWER_EFFICIENT,
                           0);
     BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
            !system_unbound_wq || !system_freezable_wq ||
            !system_power_efficient_wq ||
            !system_freezable_power_efficient_wq);
 }
 
 /**
  * workqueue_init - bring workqueue subsystem fully online
  *
  * This is the latter half of two-staged workqueue subsystem initialization
  * and invoked as soon as kthreads can be created and scheduled.
  * Workqueues have been created and work items queued on them, but there
  * are no kworkers executing the work items yet.  Populate the worker pools
  * with the initial workers and enable future kworker creations.
  */
 void __init workqueue_init(void)
 {
     struct workqueue_struct *wq;
     struct worker_pool *pool;
     int cpu, bkt;
 
     /*
      * It'd be simpler to initialize NUMA in workqueue_init_early() but
      * CPU to node mapping may not be available that early on some
      * archs such as power and arm64.  As per-cpu pools created
      * previously could be missing node hint and unbound pools NUMA
      * affinity, fix them up.
      *
      * Also, while iterating workqueues, create rescuers if requested.
      */
     wq_numa_init();
 
     mutex_lock(&wq_pool_mutex);
 
     for_each_possible_cpu(cpu) {
         for_each_cpu_worker_pool(pool, cpu) {
             pool->node = cpu_to_node(cpu);
         }
     }
 
     list_for_each_entry(wq, &workqueues, list) {
         wq_update_unbound_numa(wq, smp_processor_id(), true);
         WARN(init_rescuer(wq),
              "workqueue: failed to create early rescuer for %s",
              wq->name);
     }
 
     mutex_unlock(&wq_pool_mutex);
 
     /* create the initial workers */
     for_each_online_cpu(cpu) {
         for_each_cpu_worker_pool(pool, cpu) {
             pool->flags &= ~POOL_DISASSOCIATED;
             BUG_ON(!create_worker(pool));
         }
     }
 
     hash_for_each(unbound_pool_hash, bkt, pool, hash_node)
         BUG_ON(!create_worker(pool));
 
     wq_online = true;
     wq_watchdog_init();
 }
 
 /*
  * Despite the naming, this is a no-op function which is here only for avoiding
  * link error. Since compile-time warning may fail to catch, we will need to
  * emit run-time warning from __flush_workqueue().
  */
 void __warn_flushing_systemwide_wq(void) { }
 EXPORT_SYMBOL(__warn_flushing_systemwide_wq);