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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Common Block IO controller cgroup interface
  *
  * Based on ideas and code from CFQ, CFS and BFQ:
  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
  *
  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
  *            Paolo Valente <paolo.valente@unimore.it>
  *
  * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
  *                Nauman Rafique <nauman@google.com>
  *
  * For policy-specific per-blkcg data:
  * Copyright (C) 2015 Paolo Valente <paolo.valente@unimore.it>
  *                    Arianna Avanzini <avanzini.arianna@gmail.com>
  */
 #include <linux/ioprio.h>
 #include <linux/kdev_t.h>
 #include <linux/module.h>
 #include <linux/sched/signal.h>
 #include <linux/err.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
 #include <linux/slab.h>
 #include <linux/delay.h>
 #include <linux/atomic.h>
 #include <linux/ctype.h>
 #include <linux/resume_user_mode.h>
 #include <linux/psi.h>
 #include <linux/part_stat.h>
 #include "blk.h"
 #include "blk-cgroup.h"
 #include "blk-ioprio.h"
 #include "blk-throttle.h"
 
 /*
  * blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation.
  * blkcg_pol_register_mutex nests outside of it and synchronizes entire
  * policy [un]register operations including cgroup file additions /
  * removals.  Putting cgroup file registration outside blkcg_pol_mutex
  * allows grabbing it from cgroup callbacks.
  */
 static DEFINE_MUTEX(blkcg_pol_register_mutex);
 static DEFINE_MUTEX(blkcg_pol_mutex);
 
 struct blkcg blkcg_root;
 EXPORT_SYMBOL_GPL(blkcg_root);
 
 struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
 EXPORT_SYMBOL_GPL(blkcg_root_css);
 
 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
 
 static LIST_HEAD(all_blkcgs);       /* protected by blkcg_pol_mutex */
 
 bool blkcg_debug_stats = false;
 static struct workqueue_struct *blkcg_punt_bio_wq;
 
 #define BLKG_DESTROY_BATCH_SIZE  64
 
 /**
  * blkcg_css - find the current css
  *
  * Find the css associated with either the kthread or the current task.
  * This may return a dying css, so it is up to the caller to use tryget logic
  * to confirm it is alive and well.
  */
 static struct cgroup_subsys_state *blkcg_css(void)
 {
     struct cgroup_subsys_state *css;
 
     css = kthread_blkcg();
     if (css)
         return css;
     return task_css(current, io_cgrp_id);
 }
 
 static bool blkcg_policy_enabled(struct request_queue *q,
                  const struct blkcg_policy *pol)
 {
     return pol && test_bit(pol->plid, q->blkcg_pols);
 }
 
 static void blkg_free_workfn(struct work_struct *work)
 {
     struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
                          free_work);
     int i;
 
     for (i = 0; i < BLKCG_MAX_POLS; i++)
         if (blkg->pd[i])
             blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
 
     if (blkg->q)
         blk_put_queue(blkg->q);
     free_percpu(blkg->iostat_cpu);
     percpu_ref_exit(&blkg->refcnt);
     kfree(blkg);
 }
 
 /**
  * blkg_free - free a blkg
  * @blkg: blkg to free
  *
  * Free @blkg which may be partially allocated.
  */
 static void blkg_free(struct blkcg_gq *blkg)
 {
     if (!blkg)
         return;
 
     /*
      * Both ->pd_free_fn() and request queue's release handler may
      * sleep, so free us by scheduling one work func
      */
     INIT_WORK(&blkg->free_work, blkg_free_workfn);
     schedule_work(&blkg->free_work);
 }
 
 static void __blkg_release(struct rcu_head *rcu)
 {
     struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
 
     WARN_ON(!bio_list_empty(&blkg->async_bios));
 
     /* release the blkcg and parent blkg refs this blkg has been holding */
     css_put(&blkg->blkcg->css);
     if (blkg->parent)
         blkg_put(blkg->parent);
     blkg_free(blkg);
 }
 
 /*
  * A group is RCU protected, but having an rcu lock does not mean that one
  * can access all the fields of blkg and assume these are valid.  For
  * example, don't try to follow throtl_data and request queue links.
  *
  * Having a reference to blkg under an rcu allows accesses to only values
  * local to groups like group stats and group rate limits.
  */
 static void blkg_release(struct percpu_ref *ref)
 {
     struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
 
     call_rcu(&blkg->rcu_head, __blkg_release);
 }
 
 static void blkg_async_bio_workfn(struct work_struct *work)
 {
     struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
                          async_bio_work);
     struct bio_list bios = BIO_EMPTY_LIST;
     struct bio *bio;
     struct blk_plug plug;
     bool need_plug = false;
 
     /* as long as there are pending bios, @blkg can't go away */
     spin_lock_bh(&blkg->async_bio_lock);
     bio_list_merge(&bios, &blkg->async_bios);
     bio_list_init(&blkg->async_bios);
     spin_unlock_bh(&blkg->async_bio_lock);
 
     /* start plug only when bio_list contains at least 2 bios */
     if (bios.head && bios.head->bi_next) {
         need_plug = true;
         blk_start_plug(&plug);
     }
     while ((bio = bio_list_pop(&bios)))
         submit_bio(bio);
     if (need_plug)
         blk_finish_plug(&plug);
 }
 
 /**
  * bio_blkcg_css - return the blkcg CSS associated with a bio
  * @bio: target bio
  *
  * This returns the CSS for the blkcg associated with a bio, or %NULL if not
  * associated. Callers are expected to either handle %NULL or know association
  * has been done prior to calling this.
  */
 struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
 {
     if (!bio || !bio->bi_blkg)
         return NULL;
     return &bio->bi_blkg->blkcg->css;
 }
 EXPORT_SYMBOL_GPL(bio_blkcg_css);
 
 /**
  * blkcg_parent - get the parent of a blkcg
  * @blkcg: blkcg of interest
  *
  * Return the parent blkcg of @blkcg.  Can be called anytime.
  */
 static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
 {
     return css_to_blkcg(blkcg->css.parent);
 }
 
 /**
  * blkg_alloc - allocate a blkg
  * @blkcg: block cgroup the new blkg is associated with
  * @q: request_queue the new blkg is associated with
  * @gfp_mask: allocation mask to use
  *
  * Allocate a new blkg assocating @blkcg and @q.
  */
 static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
                    gfp_t gfp_mask)
 {
     struct blkcg_gq *blkg;
     int i, cpu;
 
     /* alloc and init base part */
     blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
     if (!blkg)
         return NULL;
 
     if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
         goto err_free;
 
     blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
     if (!blkg->iostat_cpu)
         goto err_free;
 
     if (!blk_get_queue(q))
         goto err_free;
 
     blkg->q = q;
     INIT_LIST_HEAD(&blkg->q_node);
     spin_lock_init(&blkg->async_bio_lock);
     bio_list_init(&blkg->async_bios);
     INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
     blkg->blkcg = blkcg;
 
     u64_stats_init(&blkg->iostat.sync);
     for_each_possible_cpu(cpu)
         u64_stats_init(&per_cpu_ptr(blkg->iostat_cpu, cpu)->sync);
 
     for (i = 0; i < BLKCG_MAX_POLS; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
         struct blkg_policy_data *pd;
 
         if (!blkcg_policy_enabled(q, pol))
             continue;
 
         /* alloc per-policy data and attach it to blkg */
         pd = pol->pd_alloc_fn(gfp_mask, q, blkcg);
         if (!pd)
             goto err_free;
 
         blkg->pd[i] = pd;
         pd->blkg = blkg;
         pd->plid = i;
     }
 
     return blkg;
 
 err_free:
     blkg_free(blkg);
     return NULL;
 }
 
 struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
                       struct request_queue *q, bool update_hint)
 {
     struct blkcg_gq *blkg;
 
     /*
      * Hint didn't match.  Look up from the radix tree.  Note that the
      * hint can only be updated under queue_lock as otherwise @blkg
      * could have already been removed from blkg_tree.  The caller is
      * responsible for grabbing queue_lock if @update_hint.
      */
     blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
     if (blkg && blkg->q == q) {
         if (update_hint) {
             lockdep_assert_held(&q->queue_lock);
             rcu_assign_pointer(blkcg->blkg_hint, blkg);
         }
         return blkg;
     }
 
     return NULL;
 }
 EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
 
 /*
  * If @new_blkg is %NULL, this function tries to allocate a new one as
  * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
  */
 static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
                     struct request_queue *q,
                     struct blkcg_gq *new_blkg)
 {
     struct blkcg_gq *blkg;
     int i, ret;
 
     lockdep_assert_held(&q->queue_lock);
 
     /* request_queue is dying, do not create/recreate a blkg */
     if (blk_queue_dying(q)) {
         ret = -ENODEV;
         goto err_free_blkg;
     }
 
     /* blkg holds a reference to blkcg */
     if (!css_tryget_online(&blkcg->css)) {
         ret = -ENODEV;
         goto err_free_blkg;
     }
 
     /* allocate */
     if (!new_blkg) {
         new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
         if (unlikely(!new_blkg)) {
             ret = -ENOMEM;
             goto err_put_css;
         }
     }
     blkg = new_blkg;
 
     /* link parent */
     if (blkcg_parent(blkcg)) {
         blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
         if (WARN_ON_ONCE(!blkg->parent)) {
             ret = -ENODEV;
             goto err_put_css;
         }
         blkg_get(blkg->parent);
     }
 
     /* invoke per-policy init */
     for (i = 0; i < BLKCG_MAX_POLS; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
 
         if (blkg->pd[i] && pol->pd_init_fn)
             pol->pd_init_fn(blkg->pd[i]);
     }
 
     /* insert */
     spin_lock(&blkcg->lock);
     ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
     if (likely(!ret)) {
         hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
         list_add(&blkg->q_node, &q->blkg_list);
 
         for (i = 0; i < BLKCG_MAX_POLS; i++) {
             struct blkcg_policy *pol = blkcg_policy[i];
 
             if (blkg->pd[i] && pol->pd_online_fn)
                 pol->pd_online_fn(blkg->pd[i]);
         }
     }
     blkg->online = true;
     spin_unlock(&blkcg->lock);
 
     if (!ret)
         return blkg;
 
     /* @blkg failed fully initialized, use the usual release path */
     blkg_put(blkg);
     return ERR_PTR(ret);
 
 err_put_css:
     css_put(&blkcg->css);
 err_free_blkg:
     blkg_free(new_blkg);
     return ERR_PTR(ret);
 }
 
 /**
  * blkg_lookup_create - lookup blkg, try to create one if not there
  * @blkcg: blkcg of interest
  * @q: request_queue of interest
  *
  * Lookup blkg for the @blkcg - @q pair.  If it doesn't exist, try to
  * create one.  blkg creation is performed recursively from blkcg_root such
  * that all non-root blkg's have access to the parent blkg.  This function
  * should be called under RCU read lock and takes @q->queue_lock.
  *
  * Returns the blkg or the closest blkg if blkg_create() fails as it walks
  * down from root.
  */
 static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
         struct request_queue *q)
 {
     struct blkcg_gq *blkg;
     unsigned long flags;
 
     WARN_ON_ONCE(!rcu_read_lock_held());
 
     blkg = blkg_lookup(blkcg, q);
     if (blkg)
         return blkg;
 
     spin_lock_irqsave(&q->queue_lock, flags);
     blkg = __blkg_lookup(blkcg, q, true);
     if (blkg)
         goto found;
 
     /*
      * Create blkgs walking down from blkcg_root to @blkcg, so that all
      * non-root blkgs have access to their parents.  Returns the closest
      * blkg to the intended blkg should blkg_create() fail.
      */
     while (true) {
         struct blkcg *pos = blkcg;
         struct blkcg *parent = blkcg_parent(blkcg);
         struct blkcg_gq *ret_blkg = q->root_blkg;
 
         while (parent) {
             blkg = __blkg_lookup(parent, q, false);
             if (blkg) {
                 /* remember closest blkg */
                 ret_blkg = blkg;
                 break;
             }
             pos = parent;
             parent = blkcg_parent(parent);
         }
 
         blkg = blkg_create(pos, q, NULL);
         if (IS_ERR(blkg)) {
             blkg = ret_blkg;
             break;
         }
         if (pos == blkcg)
             break;
     }
 
 found:
     spin_unlock_irqrestore(&q->queue_lock, flags);
     return blkg;
 }
 
 static void blkg_destroy(struct blkcg_gq *blkg)
 {
     struct blkcg *blkcg = blkg->blkcg;
     int i;
 
     lockdep_assert_held(&blkg->q->queue_lock);
     lockdep_assert_held(&blkcg->lock);
 
     /* Something wrong if we are trying to remove same group twice */
     WARN_ON_ONCE(list_empty(&blkg->q_node));
     WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
 
     for (i = 0; i < BLKCG_MAX_POLS; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
 
         if (blkg->pd[i] && pol->pd_offline_fn)
             pol->pd_offline_fn(blkg->pd[i]);
     }
 
     blkg->online = false;
 
     radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
     list_del_init(&blkg->q_node);
     hlist_del_init_rcu(&blkg->blkcg_node);
 
     /*
      * Both setting lookup hint to and clearing it from @blkg are done
      * under queue_lock.  If it's not pointing to @blkg now, it never
      * will.  Hint assignment itself can race safely.
      */
     if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
         rcu_assign_pointer(blkcg->blkg_hint, NULL);
 
     /*
      * Put the reference taken at the time of creation so that when all
      * queues are gone, group can be destroyed.
      */
     percpu_ref_kill(&blkg->refcnt);
 }
 
 /**
  * blkg_destroy_all - destroy all blkgs associated with a request_queue
  * @q: request_queue of interest
  *
  * Destroy all blkgs associated with @q.
  */
 static void blkg_destroy_all(struct request_queue *q)
 {
     struct blkcg_gq *blkg, *n;
     int count = BLKG_DESTROY_BATCH_SIZE;
 
 restart:
     spin_lock_irq(&q->queue_lock);
     list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
         struct blkcg *blkcg = blkg->blkcg;
 
         spin_lock(&blkcg->lock);
         blkg_destroy(blkg);
         spin_unlock(&blkcg->lock);
 
         /*
          * in order to avoid holding the spin lock for too long, release
          * it when a batch of blkgs are destroyed.
          */
         if (!(--count)) {
             count = BLKG_DESTROY_BATCH_SIZE;
             spin_unlock_irq(&q->queue_lock);
             cond_resched();
             goto restart;
         }
     }
 
     q->root_blkg = NULL;
     spin_unlock_irq(&q->queue_lock);
 }
 
 static int blkcg_reset_stats(struct cgroup_subsys_state *css,
                  struct cftype *cftype, u64 val)
 {
     struct blkcg *blkcg = css_to_blkcg(css);
     struct blkcg_gq *blkg;
     int i, cpu;
 
     mutex_lock(&blkcg_pol_mutex);
     spin_lock_irq(&blkcg->lock);
 
     /*
      * Note that stat reset is racy - it doesn't synchronize against
      * stat updates.  This is a debug feature which shouldn't exist
      * anyway.  If you get hit by a race, retry.
      */
     hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
         for_each_possible_cpu(cpu) {
             struct blkg_iostat_set *bis =
                 per_cpu_ptr(blkg->iostat_cpu, cpu);
             memset(bis, 0, sizeof(*bis));
         }
         memset(&blkg->iostat, 0, sizeof(blkg->iostat));
 
         for (i = 0; i < BLKCG_MAX_POLS; i++) {
             struct blkcg_policy *pol = blkcg_policy[i];
 
             if (blkg->pd[i] && pol->pd_reset_stats_fn)
                 pol->pd_reset_stats_fn(blkg->pd[i]);
         }
     }
 
     spin_unlock_irq(&blkcg->lock);
     mutex_unlock(&blkcg_pol_mutex);
     return 0;
 }
 
 const char *blkg_dev_name(struct blkcg_gq *blkg)
 {
     if (!blkg->q->disk || !blkg->q->disk->bdi->dev)
         return NULL;
     return bdi_dev_name(blkg->q->disk->bdi);
 }
 
 /**
  * blkcg_print_blkgs - helper for printing per-blkg data
  * @sf: seq_file to print to
  * @blkcg: blkcg of interest
  * @prfill: fill function to print out a blkg
  * @pol: policy in question
  * @data: data to be passed to @prfill
  * @show_total: to print out sum of prfill return values or not
  *
  * This function invokes @prfill on each blkg of @blkcg if pd for the
  * policy specified by @pol exists.  @prfill is invoked with @sf, the
  * policy data and @data and the matching queue lock held.  If @show_total
  * is %true, the sum of the return values from @prfill is printed with
  * "Total" label at the end.
  *
  * This is to be used to construct print functions for
  * cftype->read_seq_string method.
  */
 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
                u64 (*prfill)(struct seq_file *,
                      struct blkg_policy_data *, int),
                const struct blkcg_policy *pol, int data,
                bool show_total)
 {
     struct blkcg_gq *blkg;
     u64 total = 0;
 
     rcu_read_lock();
     hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
         spin_lock_irq(&blkg->q->queue_lock);
         if (blkcg_policy_enabled(blkg->q, pol))
             total += prfill(sf, blkg->pd[pol->plid], data);
         spin_unlock_irq(&blkg->q->queue_lock);
     }
     rcu_read_unlock();
 
     if (show_total)
         seq_printf(sf, "Total %llu\n", (unsigned long long)total);
 }
 EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
 
 /**
  * __blkg_prfill_u64 - prfill helper for a single u64 value
  * @sf: seq_file to print to
  * @pd: policy private data of interest
  * @v: value to print
  *
  * Print @v to @sf for the device assocaited with @pd.
  */
 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
 {
     const char *dname = blkg_dev_name(pd->blkg);
 
     if (!dname)
         return 0;
 
     seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
     return v;
 }
 EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
 
 /* Performs queue bypass and policy enabled checks then looks up blkg. */
 static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
                       const struct blkcg_policy *pol,
                       struct request_queue *q)
 {
     WARN_ON_ONCE(!rcu_read_lock_held());
     lockdep_assert_held(&q->queue_lock);
 
     if (!blkcg_policy_enabled(q, pol))
         return ERR_PTR(-EOPNOTSUPP);
     return __blkg_lookup(blkcg, q, true /* update_hint */);
 }
 
 /**
  * blkcg_conf_open_bdev - parse and open bdev for per-blkg config update
  * @inputp: input string pointer
  *
  * Parse the device node prefix part, MAJ:MIN, of per-blkg config update
  * from @input and get and return the matching bdev.  *@inputp is
  * updated to point past the device node prefix.  Returns an ERR_PTR()
  * value on error.
  *
  * Use this function iff blkg_conf_prep() can't be used for some reason.
  */
 struct block_device *blkcg_conf_open_bdev(char **inputp)
 {
     char *input = *inputp;
     unsigned int major, minor;
     struct block_device *bdev;
     int key_len;
 
     if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
         return ERR_PTR(-EINVAL);
 
     input += key_len;
     if (!isspace(*input))
         return ERR_PTR(-EINVAL);
     input = skip_spaces(input);
 
     bdev = blkdev_get_no_open(MKDEV(major, minor));
     if (!bdev)
         return ERR_PTR(-ENODEV);
     if (bdev_is_partition(bdev)) {
         blkdev_put_no_open(bdev);
         return ERR_PTR(-ENODEV);
     }
 
     *inputp = input;
     return bdev;
 }
 
 /**
  * blkg_conf_prep - parse and prepare for per-blkg config update
  * @blkcg: target block cgroup
  * @pol: target policy
  * @input: input string
  * @ctx: blkg_conf_ctx to be filled
  *
  * Parse per-blkg config update from @input and initialize @ctx with the
  * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
  * part of @input following MAJ:MIN.  This function returns with RCU read
  * lock and queue lock held and must be paired with blkg_conf_finish().
  */
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
            char *input, struct blkg_conf_ctx *ctx)
     __acquires(rcu) __acquires(&bdev->bd_queue->queue_lock)
 {
     struct block_device *bdev;
     struct request_queue *q;
     struct blkcg_gq *blkg;
     int ret;
 
     bdev = blkcg_conf_open_bdev(&input);
     if (IS_ERR(bdev))
         return PTR_ERR(bdev);
 
     q = bdev_get_queue(bdev);
 
     /*
      * blkcg_deactivate_policy() requires queue to be frozen, we can grab
      * q_usage_counter to prevent concurrent with blkcg_deactivate_policy().
      */
     ret = blk_queue_enter(q, 0);
     if (ret)
         goto fail;
 
     rcu_read_lock();
     spin_lock_irq(&q->queue_lock);
 
     blkg = blkg_lookup_check(blkcg, pol, q);
     if (IS_ERR(blkg)) {
         ret = PTR_ERR(blkg);
         goto fail_unlock;
     }
 
     if (blkg)
         goto success;
 
     /*
      * Create blkgs walking down from blkcg_root to @blkcg, so that all
      * non-root blkgs have access to their parents.
      */
     while (true) {
         struct blkcg *pos = blkcg;
         struct blkcg *parent;
         struct blkcg_gq *new_blkg;
 
         parent = blkcg_parent(blkcg);
         while (parent && !__blkg_lookup(parent, q, false)) {
             pos = parent;
             parent = blkcg_parent(parent);
         }
 
         /* Drop locks to do new blkg allocation with GFP_KERNEL. */
         spin_unlock_irq(&q->queue_lock);
         rcu_read_unlock();
 
         new_blkg = blkg_alloc(pos, q, GFP_KERNEL);
         if (unlikely(!new_blkg)) {
             ret = -ENOMEM;
             goto fail_exit_queue;
         }
 
         if (radix_tree_preload(GFP_KERNEL)) {
             blkg_free(new_blkg);
             ret = -ENOMEM;
             goto fail_exit_queue;
         }
 
         rcu_read_lock();
         spin_lock_irq(&q->queue_lock);
 
         blkg = blkg_lookup_check(pos, pol, q);
         if (IS_ERR(blkg)) {
             ret = PTR_ERR(blkg);
             blkg_free(new_blkg);
             goto fail_preloaded;
         }
 
         if (blkg) {
             blkg_free(new_blkg);
         } else {
             blkg = blkg_create(pos, q, new_blkg);
             if (IS_ERR(blkg)) {
                 ret = PTR_ERR(blkg);
                 goto fail_preloaded;
             }
         }
 
         radix_tree_preload_end();
 
         if (pos == blkcg)
             goto success;
     }
 success:
     blk_queue_exit(q);
     ctx->bdev = bdev;
     ctx->blkg = blkg;
     ctx->body = input;
     return 0;
 
 fail_preloaded:
     radix_tree_preload_end();
 fail_unlock:
     spin_unlock_irq(&q->queue_lock);
     rcu_read_unlock();
 fail_exit_queue:
     blk_queue_exit(q);
 fail:
     blkdev_put_no_open(bdev);
     /*
      * If queue was bypassing, we should retry.  Do so after a
      * short msleep().  It isn't strictly necessary but queue
      * can be bypassing for some time and it's always nice to
      * avoid busy looping.
      */
     if (ret == -EBUSY) {
         msleep(10);
         ret = restart_syscall();
     }
     return ret;
 }
 EXPORT_SYMBOL_GPL(blkg_conf_prep);
 
 /**
  * blkg_conf_finish - finish up per-blkg config update
  * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
  *
  * Finish up after per-blkg config update.  This function must be paired
  * with blkg_conf_prep().
  */
 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
     __releases(&ctx->bdev->bd_queue->queue_lock) __releases(rcu)
 {
     spin_unlock_irq(&bdev_get_queue(ctx->bdev)->queue_lock);
     rcu_read_unlock();
     blkdev_put_no_open(ctx->bdev);
 }
 EXPORT_SYMBOL_GPL(blkg_conf_finish);
 
 static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
 {
     int i;
 
     for (i = 0; i < BLKG_IOSTAT_NR; i++) {
         dst->bytes[i] = src->bytes[i];
         dst->ios[i] = src->ios[i];
     }
 }
 
 static void blkg_iostat_add(struct blkg_iostat *dst, struct blkg_iostat *src)
 {
     int i;
 
     for (i = 0; i < BLKG_IOSTAT_NR; i++) {
         dst->bytes[i] += src->bytes[i];
         dst->ios[i] += src->ios[i];
     }
 }
 
 static void blkg_iostat_sub(struct blkg_iostat *dst, struct blkg_iostat *src)
 {
     int i;
 
     for (i = 0; i < BLKG_IOSTAT_NR; i++) {
         dst->bytes[i] -= src->bytes[i];
         dst->ios[i] -= src->ios[i];
     }
 }
 
 static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur,
                 struct blkg_iostat *last)
 {
     struct blkg_iostat delta;
     unsigned long flags;
 
     /* propagate percpu delta to global */
     flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
     blkg_iostat_set(&delta, cur);
     blkg_iostat_sub(&delta, last);
     blkg_iostat_add(&blkg->iostat.cur, &delta);
     blkg_iostat_add(last, &delta);
     u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
 }
 
 static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 {
     struct blkcg *blkcg = css_to_blkcg(css);
     struct blkcg_gq *blkg;
 
     /* Root-level stats are sourced from system-wide IO stats */
     if (!cgroup_parent(css->cgroup))
         return;
 
     rcu_read_lock();
 
     hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
         struct blkcg_gq *parent = blkg->parent;
         struct blkg_iostat_set *bisc = per_cpu_ptr(blkg->iostat_cpu, cpu);
         struct blkg_iostat cur;
         unsigned int seq;
 
         /* fetch the current per-cpu values */
         do {
             seq = u64_stats_fetch_begin(&bisc->sync);
             blkg_iostat_set(&cur, &bisc->cur);
         } while (u64_stats_fetch_retry(&bisc->sync, seq));
 
         blkcg_iostat_update(blkg, &cur, &bisc->last);
 
         /* propagate global delta to parent (unless that's root) */
         if (parent && parent->parent)
             blkcg_iostat_update(parent, &blkg->iostat.cur,
                         &blkg->iostat.last);
     }
 
     rcu_read_unlock();
 }
 
 /*
  * We source root cgroup stats from the system-wide stats to avoid
  * tracking the same information twice and incurring overhead when no
  * cgroups are defined. For that reason, cgroup_rstat_flush in
  * blkcg_print_stat does not actually fill out the iostat in the root
  * cgroup's blkcg_gq.
  *
  * However, we would like to re-use the printing code between the root and
  * non-root cgroups to the extent possible. For that reason, we simulate
  * flushing the root cgroup's stats by explicitly filling in the iostat
  * with disk level statistics.
  */
 static void blkcg_fill_root_iostats(void)
 {
     struct class_dev_iter iter;
     struct device *dev;
 
     class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
     while ((dev = class_dev_iter_next(&iter))) {
         struct block_device *bdev = dev_to_bdev(dev);
         struct blkcg_gq *blkg =
             blk_queue_root_blkg(bdev_get_queue(bdev));
         struct blkg_iostat tmp;
         int cpu;
         unsigned long flags;
 
         memset(&tmp, 0, sizeof(tmp));
         for_each_possible_cpu(cpu) {
             struct disk_stats *cpu_dkstats;
 
             cpu_dkstats = per_cpu_ptr(bdev->bd_stats, cpu);
             tmp.ios[BLKG_IOSTAT_READ] +=
                 cpu_dkstats->ios[STAT_READ];
             tmp.ios[BLKG_IOSTAT_WRITE] +=
                 cpu_dkstats->ios[STAT_WRITE];
             tmp.ios[BLKG_IOSTAT_DISCARD] +=
                 cpu_dkstats->ios[STAT_DISCARD];
             // convert sectors to bytes
             tmp.bytes[BLKG_IOSTAT_READ] +=
                 cpu_dkstats->sectors[STAT_READ] << 9;
             tmp.bytes[BLKG_IOSTAT_WRITE] +=
                 cpu_dkstats->sectors[STAT_WRITE] << 9;
             tmp.bytes[BLKG_IOSTAT_DISCARD] +=
                 cpu_dkstats->sectors[STAT_DISCARD] << 9;
         }
 
         flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
         blkg_iostat_set(&blkg->iostat.cur, &tmp);
         u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
     }
 }
 
 static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 {
     struct blkg_iostat_set *bis = &blkg->iostat;
     u64 rbytes, wbytes, rios, wios, dbytes, dios;
     const char *dname;
     unsigned seq;
     int i;
 
     if (!blkg->online)
         return;
 
     dname = blkg_dev_name(blkg);
     if (!dname)
         return;
 
     seq_printf(s, "%s ", dname);
 
     do {
         seq = u64_stats_fetch_begin(&bis->sync);
 
         rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
         wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
         dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
         rios = bis->cur.ios[BLKG_IOSTAT_READ];
         wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
         dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
     } while (u64_stats_fetch_retry(&bis->sync, seq));
 
     if (rbytes || wbytes || rios || wios) {
         seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
             rbytes, wbytes, rios, wios,
             dbytes, dios);
     }
 
     if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
         seq_printf(s, " use_delay=%d delay_nsec=%llu",
             atomic_read(&blkg->use_delay),
             atomic64_read(&blkg->delay_nsec));
     }
 
     for (i = 0; i < BLKCG_MAX_POLS; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
 
         if (!blkg->pd[i] || !pol->pd_stat_fn)
             continue;
 
         pol->pd_stat_fn(blkg->pd[i], s);
     }
 
     seq_puts(s, "\n");
 }
 
 static int blkcg_print_stat(struct seq_file *sf, void *v)
 {
     struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
     struct blkcg_gq *blkg;
 
     if (!seq_css(sf)->parent)
         blkcg_fill_root_iostats();
     else
         cgroup_rstat_flush(blkcg->css.cgroup);
 
     rcu_read_lock();
     hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
         spin_lock_irq(&blkg->q->queue_lock);
         blkcg_print_one_stat(blkg, sf);
         spin_unlock_irq(&blkg->q->queue_lock);
     }
     rcu_read_unlock();
     return 0;
 }
 
 static struct cftype blkcg_files[] = {
     {
         .name = "stat",
         .seq_show = blkcg_print_stat,
     },
     { } /* terminate */
 };
 
 static struct cftype blkcg_legacy_files[] = {
     {
         .name = "reset_stats",
         .write_u64 = blkcg_reset_stats,
     },
     { } /* terminate */
 };
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css)
 {
     return &css_to_blkcg(css)->cgwb_list;
 }
 #endif
 
 /*
  * blkcg destruction is a three-stage process.
  *
  * 1. Destruction starts.  The blkcg_css_offline() callback is invoked
  *    which offlines writeback.  Here we tie the next stage of blkg destruction
  *    to the completion of writeback associated with the blkcg.  This lets us
  *    avoid punting potentially large amounts of outstanding writeback to root
  *    while maintaining any ongoing policies.  The next stage is triggered when
  *    the nr_cgwbs count goes to zero.
  *
  * 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
  *    and handles the destruction of blkgs.  Here the css reference held by
  *    the blkg is put back eventually allowing blkcg_css_free() to be called.
  *    This work may occur in cgwb_release_workfn() on the cgwb_release
  *    workqueue.  Any submitted ios that fail to get the blkg ref will be
  *    punted to the root_blkg.
  *
  * 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
  *    This finally frees the blkcg.
  */
 
 /**
  * blkcg_destroy_blkgs - responsible for shooting down blkgs
  * @blkcg: blkcg of interest
  *
  * blkgs should be removed while holding both q and blkcg locks.  As blkcg lock
  * is nested inside q lock, this function performs reverse double lock dancing.
  * Destroying the blkgs releases the reference held on the blkcg's css allowing
  * blkcg_css_free to eventually be called.
  *
  * This is the blkcg counterpart of ioc_release_fn().
  */
 static void blkcg_destroy_blkgs(struct blkcg *blkcg)
 {
     might_sleep();
 
     spin_lock_irq(&blkcg->lock);
 
     while (!hlist_empty(&blkcg->blkg_list)) {
         struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
                         struct blkcg_gq, blkcg_node);
         struct request_queue *q = blkg->q;
 
         if (need_resched() || !spin_trylock(&q->queue_lock)) {
             /*
              * Given that the system can accumulate a huge number
              * of blkgs in pathological cases, check to see if we
              * need to rescheduling to avoid softlockup.
              */
             spin_unlock_irq(&blkcg->lock);
             cond_resched();
             spin_lock_irq(&blkcg->lock);
             continue;
         }
 
         blkg_destroy(blkg);
         spin_unlock(&q->queue_lock);
     }
 
     spin_unlock_irq(&blkcg->lock);
 }
 
 /**
  * blkcg_pin_online - pin online state
  * @blkcg_css: blkcg of interest
  *
  * While pinned, a blkcg is kept online.  This is primarily used to
  * impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
  * while an associated cgwb is still active.
  */
 void blkcg_pin_online(struct cgroup_subsys_state *blkcg_css)
 {
     refcount_inc(&css_to_blkcg(blkcg_css)->online_pin);
 }
 
 /**
  * blkcg_unpin_online - unpin online state
  * @blkcg_css: blkcg of interest
  *
  * This is primarily used to impedance-match blkg and cgwb lifetimes so
  * that blkg doesn't go offline while an associated cgwb is still active.
  * When this count goes to zero, all active cgwbs have finished so the
  * blkcg can continue destruction by calling blkcg_destroy_blkgs().
  */
 void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css)
 {
     struct blkcg *blkcg = css_to_blkcg(blkcg_css);
 
     do {
         if (!refcount_dec_and_test(&blkcg->online_pin))
             break;
         blkcg_destroy_blkgs(blkcg);
         blkcg = blkcg_parent(blkcg);
     } while (blkcg);
 }
 
 /**
  * blkcg_css_offline - cgroup css_offline callback
  * @css: css of interest
  *
  * This function is called when @css is about to go away.  Here the cgwbs are
  * offlined first and only once writeback associated with the blkcg has
  * finished do we start step 2 (see above).
  */
 static void blkcg_css_offline(struct cgroup_subsys_state *css)
 {
     /* this prevents anyone from attaching or migrating to this blkcg */
     wb_blkcg_offline(css);
 
     /* put the base online pin allowing step 2 to be triggered */
     blkcg_unpin_online(css);
 }
 
 static void blkcg_css_free(struct cgroup_subsys_state *css)
 {
     struct blkcg *blkcg = css_to_blkcg(css);
     int i;
 
     mutex_lock(&blkcg_pol_mutex);
 
     list_del(&blkcg->all_blkcgs_node);
 
     for (i = 0; i < BLKCG_MAX_POLS; i++)
         if (blkcg->cpd[i])
             blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
 
     mutex_unlock(&blkcg_pol_mutex);
 
     kfree(blkcg);
 }
 
 static struct cgroup_subsys_state *
 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 {
     struct blkcg *blkcg;
     struct cgroup_subsys_state *ret;
     int i;
 
     mutex_lock(&blkcg_pol_mutex);
 
     if (!parent_css) {
         blkcg = &blkcg_root;
     } else {
         blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
         if (!blkcg) {
             ret = ERR_PTR(-ENOMEM);
             goto unlock;
         }
     }
 
     for (i = 0; i < BLKCG_MAX_POLS ; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
         struct blkcg_policy_data *cpd;
 
         /*
          * If the policy hasn't been attached yet, wait for it
          * to be attached before doing anything else. Otherwise,
          * check if the policy requires any specific per-cgroup
          * data: if it does, allocate and initialize it.
          */
         if (!pol || !pol->cpd_alloc_fn)
             continue;
 
         cpd = pol->cpd_alloc_fn(GFP_KERNEL);
         if (!cpd) {
             ret = ERR_PTR(-ENOMEM);
             goto free_pd_blkcg;
         }
         blkcg->cpd[i] = cpd;
         cpd->blkcg = blkcg;
         cpd->plid = i;
         if (pol->cpd_init_fn)
             pol->cpd_init_fn(cpd);
     }
 
     spin_lock_init(&blkcg->lock);
     refcount_set(&blkcg->online_pin, 1);
     INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
     INIT_HLIST_HEAD(&blkcg->blkg_list);
 #ifdef CONFIG_CGROUP_WRITEBACK
     INIT_LIST_HEAD(&blkcg->cgwb_list);
 #endif
     list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
 
     mutex_unlock(&blkcg_pol_mutex);
     return &blkcg->css;
 
 free_pd_blkcg:
     for (i--; i >= 0; i--)
         if (blkcg->cpd[i])
             blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
 
     if (blkcg != &blkcg_root)
         kfree(blkcg);
 unlock:
     mutex_unlock(&blkcg_pol_mutex);
     return ret;
 }
 
 static int blkcg_css_online(struct cgroup_subsys_state *css)
 {
     struct blkcg *parent = blkcg_parent(css_to_blkcg(css));
 
     /*
      * blkcg_pin_online() is used to delay blkcg offline so that blkgs
      * don't go offline while cgwbs are still active on them.  Pin the
      * parent so that offline always happens towards the root.
      */
     if (parent)
         blkcg_pin_online(css);
     return 0;
 }
 
 /**
  * blkcg_init_queue - initialize blkcg part of request queue
  * @q: request_queue to initialize
  *
  * Called from blk_alloc_queue(). Responsible for initializing blkcg
  * part of new request_queue @q.
  *
  * RETURNS:
  * 0 on success, -errno on failure.
  */
 int blkcg_init_queue(struct request_queue *q)
 {
     struct blkcg_gq *new_blkg, *blkg;
     bool preloaded;
     int ret;
 
     INIT_LIST_HEAD(&q->blkg_list);
 
     new_blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
     if (!new_blkg)
         return -ENOMEM;
 
     preloaded = !radix_tree_preload(GFP_KERNEL);
 
     /* Make sure the root blkg exists. */
     /* spin_lock_irq can serve as RCU read-side critical section. */
     spin_lock_irq(&q->queue_lock);
     blkg = blkg_create(&blkcg_root, q, new_blkg);
     if (IS_ERR(blkg))
         goto err_unlock;
     q->root_blkg = blkg;
     spin_unlock_irq(&q->queue_lock);
 
     if (preloaded)
         radix_tree_preload_end();
 
     ret = blk_ioprio_init(q);
     if (ret)
         goto err_destroy_all;
 
     ret = blk_throtl_init(q);
     if (ret)
         goto err_destroy_all;
 
     ret = blk_iolatency_init(q);
     if (ret) {
         blk_throtl_exit(q);
         blk_ioprio_exit(q);
         goto err_destroy_all;
     }
 
     return 0;
 
 err_destroy_all:
     blkg_destroy_all(q);
     return ret;
 err_unlock:
     spin_unlock_irq(&q->queue_lock);
     if (preloaded)
         radix_tree_preload_end();
     return PTR_ERR(blkg);
 }
 
 /**
  * blkcg_exit_queue - exit and release blkcg part of request_queue
  * @q: request_queue being released
  *
  * Called from blk_exit_queue().  Responsible for exiting blkcg part.
  */
 void blkcg_exit_queue(struct request_queue *q)
 {
     blkg_destroy_all(q);
     blk_throtl_exit(q);
 }
 
 static void blkcg_bind(struct cgroup_subsys_state *root_css)
 {
     int i;
 
     mutex_lock(&blkcg_pol_mutex);
 
     for (i = 0; i < BLKCG_MAX_POLS; i++) {
         struct blkcg_policy *pol = blkcg_policy[i];
         struct blkcg *blkcg;
 
         if (!pol || !pol->cpd_bind_fn)
             continue;
 
         list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node)
             if (blkcg->cpd[pol->plid])
                 pol->cpd_bind_fn(blkcg->cpd[pol->plid]);
     }
     mutex_unlock(&blkcg_pol_mutex);
 }
 
 static void blkcg_exit(struct task_struct *tsk)
 {
     if (tsk->throttle_queue)
         blk_put_queue(tsk->throttle_queue);
     tsk->throttle_queue = NULL;
 }
 
 struct cgroup_subsys io_cgrp_subsys = {
     .css_alloc = blkcg_css_alloc,
     .css_online = blkcg_css_online,
     .css_offline = blkcg_css_offline,
     .css_free = blkcg_css_free,
     .css_rstat_flush = blkcg_rstat_flush,
     .bind = blkcg_bind,
     .dfl_cftypes = blkcg_files,
     .legacy_cftypes = blkcg_legacy_files,
     .legacy_name = "blkio",
     .exit = blkcg_exit,
 #ifdef CONFIG_MEMCG
     /*
      * This ensures that, if available, memcg is automatically enabled
      * together on the default hierarchy so that the owner cgroup can
      * be retrieved from writeback pages.
      */
     .depends_on = 1 << memory_cgrp_id,
 #endif
 };
 EXPORT_SYMBOL_GPL(io_cgrp_subsys);
 
 /**
  * blkcg_activate_policy - activate a blkcg policy on a request_queue
  * @q: request_queue of interest
  * @pol: blkcg policy to activate
  *
  * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
  * bypass mode to populate its blkgs with policy_data for @pol.
  *
  * Activation happens with @q bypassed, so nobody would be accessing blkgs
  * from IO path.  Update of each blkg is protected by both queue and blkcg
  * locks so that holding either lock and testing blkcg_policy_enabled() is
  * always enough for dereferencing policy data.
  *
  * The caller is responsible for synchronizing [de]activations and policy
  * [un]registerations.  Returns 0 on success, -errno on failure.
  */
 int blkcg_activate_policy(struct request_queue *q,
               const struct blkcg_policy *pol)
 {
     struct blkg_policy_data *pd_prealloc = NULL;
     struct blkcg_gq *blkg, *pinned_blkg = NULL;
     int ret;
 
     if (blkcg_policy_enabled(q, pol))
         return 0;
 
     if (queue_is_mq(q))
         blk_mq_freeze_queue(q);
 retry:
     spin_lock_irq(&q->queue_lock);
 
     /* blkg_list is pushed at the head, reverse walk to allocate parents first */
     list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
         struct blkg_policy_data *pd;
 
         if (blkg->pd[pol->plid])
             continue;
 
         /* If prealloc matches, use it; otherwise try GFP_NOWAIT */
         if (blkg == pinned_blkg) {
             pd = pd_prealloc;
             pd_prealloc = NULL;
         } else {
             pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q,
                           blkg->blkcg);
         }
 
         if (!pd) {
             /*
              * GFP_NOWAIT failed.  Free the existing one and
              * prealloc for @blkg w/ GFP_KERNEL.
              */
             if (pinned_blkg)
                 blkg_put(pinned_blkg);
             blkg_get(blkg);
             pinned_blkg = blkg;
 
             spin_unlock_irq(&q->queue_lock);
 
             if (pd_prealloc)
                 pol->pd_free_fn(pd_prealloc);
             pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q,
                                blkg->blkcg);
             if (pd_prealloc)
                 goto retry;
             else
                 goto enomem;
         }
 
         blkg->pd[pol->plid] = pd;
         pd->blkg = blkg;
         pd->plid = pol->plid;
     }
 
     /* all allocated, init in the same order */
     if (pol->pd_init_fn)
         list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
             pol->pd_init_fn(blkg->pd[pol->plid]);
 
     __set_bit(pol->plid, q->blkcg_pols);
     ret = 0;
 
     spin_unlock_irq(&q->queue_lock);
 out:
     if (queue_is_mq(q))
         blk_mq_unfreeze_queue(q);
     if (pinned_blkg)
         blkg_put(pinned_blkg);
     if (pd_prealloc)
         pol->pd_free_fn(pd_prealloc);
     return ret;
 
 enomem:
     /* alloc failed, nothing's initialized yet, free everything */
     spin_lock_irq(&q->queue_lock);
     list_for_each_entry(blkg, &q->blkg_list, q_node) {
         struct blkcg *blkcg = blkg->blkcg;
 
         spin_lock(&blkcg->lock);
         if (blkg->pd[pol->plid]) {
             pol->pd_free_fn(blkg->pd[pol->plid]);
             blkg->pd[pol->plid] = NULL;
         }
         spin_unlock(&blkcg->lock);
     }
     spin_unlock_irq(&q->queue_lock);
     ret = -ENOMEM;
     goto out;
 }
 EXPORT_SYMBOL_GPL(blkcg_activate_policy);
 
 /**
  * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
  * @q: request_queue of interest
  * @pol: blkcg policy to deactivate
  *
  * Deactivate @pol on @q.  Follows the same synchronization rules as
  * blkcg_activate_policy().
  */
 void blkcg_deactivate_policy(struct request_queue *q,
                  const struct blkcg_policy *pol)
 {
     struct blkcg_gq *blkg;
 
     if (!blkcg_policy_enabled(q, pol))
         return;
 
     if (queue_is_mq(q))
         blk_mq_freeze_queue(q);
 
     spin_lock_irq(&q->queue_lock);
 
     __clear_bit(pol->plid, q->blkcg_pols);
 
     list_for_each_entry(blkg, &q->blkg_list, q_node) {
         struct blkcg *blkcg = blkg->blkcg;
 
         spin_lock(&blkcg->lock);
         if (blkg->pd[pol->plid]) {
             if (pol->pd_offline_fn)
                 pol->pd_offline_fn(blkg->pd[pol->plid]);
             pol->pd_free_fn(blkg->pd[pol->plid]);
             blkg->pd[pol->plid] = NULL;
         }
         spin_unlock(&blkcg->lock);
     }
 
     spin_unlock_irq(&q->queue_lock);
 
     if (queue_is_mq(q))
         blk_mq_unfreeze_queue(q);
 }
 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
 
 static void blkcg_free_all_cpd(struct blkcg_policy *pol)
 {
     struct blkcg *blkcg;
 
     list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
         if (blkcg->cpd[pol->plid]) {
             pol->cpd_free_fn(blkcg->cpd[pol->plid]);
             blkcg->cpd[pol->plid] = NULL;
         }
     }
 }
 
 /**
  * blkcg_policy_register - register a blkcg policy
  * @pol: blkcg policy to register
  *
  * Register @pol with blkcg core.  Might sleep and @pol may be modified on
  * successful registration.  Returns 0 on success and -errno on failure.
  */
 int blkcg_policy_register(struct blkcg_policy *pol)
 {
     struct blkcg *blkcg;
     int i, ret;
 
     mutex_lock(&blkcg_pol_register_mutex);
     mutex_lock(&blkcg_pol_mutex);
 
     /* find an empty slot */
     ret = -ENOSPC;
     for (i = 0; i < BLKCG_MAX_POLS; i++)
         if (!blkcg_policy[i])
             break;
     if (i >= BLKCG_MAX_POLS) {
         pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
         goto err_unlock;
     }
 
     /* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
     if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
         (!pol->pd_alloc_fn ^ !pol->pd_free_fn))
         goto err_unlock;
 
     /* register @pol */
     pol->plid = i;
     blkcg_policy[pol->plid] = pol;
 
     /* allocate and install cpd's */
     if (pol->cpd_alloc_fn) {
         list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
             struct blkcg_policy_data *cpd;
 
             cpd = pol->cpd_alloc_fn(GFP_KERNEL);
             if (!cpd)
                 goto err_free_cpds;
 
             blkcg->cpd[pol->plid] = cpd;
             cpd->blkcg = blkcg;
             cpd->plid = pol->plid;
             if (pol->cpd_init_fn)
                 pol->cpd_init_fn(cpd);
         }
     }
 
     mutex_unlock(&blkcg_pol_mutex);
 
     /* everything is in place, add intf files for the new policy */
     if (pol->dfl_cftypes)
         WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
                            pol->dfl_cftypes));
     if (pol->legacy_cftypes)
         WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
                           pol->legacy_cftypes));
     mutex_unlock(&blkcg_pol_register_mutex);
     return 0;
 
 err_free_cpds:
     if (pol->cpd_free_fn)
         blkcg_free_all_cpd(pol);
 
     blkcg_policy[pol->plid] = NULL;
 err_unlock:
     mutex_unlock(&blkcg_pol_mutex);
     mutex_unlock(&blkcg_pol_register_mutex);
     return ret;
 }
 EXPORT_SYMBOL_GPL(blkcg_policy_register);
 
 /**
  * blkcg_policy_unregister - unregister a blkcg policy
  * @pol: blkcg policy to unregister
  *
  * Undo blkcg_policy_register(@pol).  Might sleep.
  */
 void blkcg_policy_unregister(struct blkcg_policy *pol)
 {
     mutex_lock(&blkcg_pol_register_mutex);
 
     if (WARN_ON(blkcg_policy[pol->plid] != pol))
         goto out_unlock;
 
     /* kill the intf files first */
     if (pol->dfl_cftypes)
         cgroup_rm_cftypes(pol->dfl_cftypes);
     if (pol->legacy_cftypes)
         cgroup_rm_cftypes(pol->legacy_cftypes);
 
     /* remove cpds and unregister */
     mutex_lock(&blkcg_pol_mutex);
 
     if (pol->cpd_free_fn)
         blkcg_free_all_cpd(pol);
 
     blkcg_policy[pol->plid] = NULL;
 
     mutex_unlock(&blkcg_pol_mutex);
 out_unlock:
     mutex_unlock(&blkcg_pol_register_mutex);
 }
 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
 
 bool __blkcg_punt_bio_submit(struct bio *bio)
 {
     struct blkcg_gq *blkg = bio->bi_blkg;
 
     /* consume the flag first */
     bio->bi_opf &= ~REQ_CGROUP_PUNT;
 
     /* never bounce for the root cgroup */
     if (!blkg->parent)
         return false;
 
     spin_lock_bh(&blkg->async_bio_lock);
     bio_list_add(&blkg->async_bios, bio);
     spin_unlock_bh(&blkg->async_bio_lock);
 
     queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
     return true;
 }
 
 /*
  * Scale the accumulated delay based on how long it has been since we updated
  * the delay.  We only call this when we are adding delay, in case it's been a
  * while since we added delay, and when we are checking to see if we need to
  * delay a task, to account for any delays that may have occurred.
  */
 static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now)
 {
     u64 old = atomic64_read(&blkg->delay_start);
 
     /* negative use_delay means no scaling, see blkcg_set_delay() */
     if (atomic_read(&blkg->use_delay) < 0)
         return;
 
     /*
      * We only want to scale down every second.  The idea here is that we
      * want to delay people for min(delay_nsec, NSEC_PER_SEC) in a certain
      * time window.  We only want to throttle tasks for recent delay that
      * has occurred, in 1 second time windows since that's the maximum
      * things can be throttled.  We save the current delay window in
      * blkg->last_delay so we know what amount is still left to be charged
      * to the blkg from this point onward.  blkg->last_use keeps track of
      * the use_delay counter.  The idea is if we're unthrottling the blkg we
      * are ok with whatever is happening now, and we can take away more of
      * the accumulated delay as we've already throttled enough that
      * everybody is happy with their IO latencies.
      */
     if (time_before64(old + NSEC_PER_SEC, now) &&
         atomic64_try_cmpxchg(&blkg->delay_start, &old, now)) {
         u64 cur = atomic64_read(&blkg->delay_nsec);
         u64 sub = min_t(u64, blkg->last_delay, now - old);
         int cur_use = atomic_read(&blkg->use_delay);
 
         /*
          * We've been unthrottled, subtract a larger chunk of our
          * accumulated delay.
          */
         if (cur_use < blkg->last_use)
             sub = max_t(u64, sub, blkg->last_delay >> 1);
 
         /*
          * This shouldn't happen, but handle it anyway.  Our delay_nsec
          * should only ever be growing except here where we subtract out
          * min(last_delay, 1 second), but lord knows bugs happen and I'd
          * rather not end up with negative numbers.
          */
         if (unlikely(cur < sub)) {
             atomic64_set(&blkg->delay_nsec, 0);
             blkg->last_delay = 0;
         } else {
             atomic64_sub(sub, &blkg->delay_nsec);
             blkg->last_delay = cur - sub;
         }
         blkg->last_use = cur_use;
     }
 }
 
 /*
  * This is called when we want to actually walk up the hierarchy and check to
  * see if we need to throttle, and then actually throttle if there is some
  * accumulated delay.  This should only be called upon return to user space so
  * we're not holding some lock that would induce a priority inversion.
  */
 static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
 {
     unsigned long pflags;
     bool clamp;
     u64 now = ktime_to_ns(ktime_get());
     u64 exp;
     u64 delay_nsec = 0;
     int tok;
 
     while (blkg->parent) {
         int use_delay = atomic_read(&blkg->use_delay);
 
         if (use_delay) {
             u64 this_delay;
 
             blkcg_scale_delay(blkg, now);
             this_delay = atomic64_read(&blkg->delay_nsec);
             if (this_delay > delay_nsec) {
                 delay_nsec = this_delay;
                 clamp = use_delay > 0;
             }
         }
         blkg = blkg->parent;
     }
 
     if (!delay_nsec)
         return;
 
     /*
      * Let's not sleep for all eternity if we've amassed a huge delay.
      * Swapping or metadata IO can accumulate 10's of seconds worth of
      * delay, and we want userspace to be able to do _something_ so cap the
      * delays at 0.25s. If there's 10's of seconds worth of delay then the
      * tasks will be delayed for 0.25 second for every syscall. If
      * blkcg_set_delay() was used as indicated by negative use_delay, the
      * caller is responsible for regulating the range.
      */
     if (clamp)
         delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
 
     if (use_memdelay)
         psi_memstall_enter(&pflags);
 
     exp = ktime_add_ns(now, delay_nsec);
     tok = io_schedule_prepare();
     do {
         __set_current_state(TASK_KILLABLE);
         if (!schedule_hrtimeout(&exp, HRTIMER_MODE_ABS))
             break;
     } while (!fatal_signal_pending(current));
     io_schedule_finish(tok);
 
     if (use_memdelay)
         psi_memstall_leave(&pflags);
 }
 
 /**
  * blkcg_maybe_throttle_current - throttle the current task if it has been marked
  *
  * This is only called if we've been marked with set_notify_resume().  Obviously
  * we can be set_notify_resume() for reasons other than blkcg throttling, so we
  * check to see if current->throttle_queue is set and if not this doesn't do
  * anything.  This should only ever be called by the resume code, it's not meant
  * to be called by people willy-nilly as it will actually do the work to
  * throttle the task if it is setup for throttling.
  */
 void blkcg_maybe_throttle_current(void)
 {
     struct request_queue *q = current->throttle_queue;
     struct blkcg *blkcg;
     struct blkcg_gq *blkg;
     bool use_memdelay = current->use_memdelay;
 
     if (!q)
         return;
 
     current->throttle_queue = NULL;
     current->use_memdelay = false;
 
     rcu_read_lock();
     blkcg = css_to_blkcg(blkcg_css());
     if (!blkcg)
         goto out;
     blkg = blkg_lookup(blkcg, q);
     if (!blkg)
         goto out;
     if (!blkg_tryget(blkg))
         goto out;
     rcu_read_unlock();
 
     blkcg_maybe_throttle_blkg(blkg, use_memdelay);
     blkg_put(blkg);
     blk_put_queue(q);
     return;
 out:
     rcu_read_unlock();
     blk_put_queue(q);
 }
 
 /**
  * blkcg_schedule_throttle - this task needs to check for throttling
  * @q: the request queue IO was submitted on
  * @use_memdelay: do we charge this to memory delay for PSI
  *
  * This is called by the IO controller when we know there's delay accumulated
  * for the blkg for this task.  We do not pass the blkg because there are places
  * we call this that may not have that information, the swapping code for
  * instance will only have a request_queue at that point.  This set's the
  * notify_resume for the task to check and see if it requires throttling before
  * returning to user space.
  *
  * We will only schedule once per syscall.  You can call this over and over
  * again and it will only do the check once upon return to user space, and only
  * throttle once.  If the task needs to be throttled again it'll need to be
  * re-set at the next time we see the task.
  */
 void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay)
 {
     if (unlikely(current->flags & PF_KTHREAD))
         return;
 
     if (current->throttle_queue != q) {
         if (!blk_get_queue(q))
             return;
 
         if (current->throttle_queue)
             blk_put_queue(current->throttle_queue);
         current->throttle_queue = q;
     }
 
     if (use_memdelay)
         current->use_memdelay = use_memdelay;
     set_notify_resume(current);
 }
 
 /**
  * blkcg_add_delay - add delay to this blkg
  * @blkg: blkg of interest
  * @now: the current time in nanoseconds
  * @delta: how many nanoseconds of delay to add
  *
  * Charge @delta to the blkg's current delay accumulation.  This is used to
  * throttle tasks if an IO controller thinks we need more throttling.
  */
 void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)
 {
     if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
         return;
     blkcg_scale_delay(blkg, now);
     atomic64_add(delta, &blkg->delay_nsec);
 }
 
 /**
  * blkg_tryget_closest - try and get a blkg ref on the closet blkg
  * @bio: target bio
  * @css: target css
  *
  * As the failure mode here is to walk up the blkg tree, this ensure that the
  * blkg->parent pointers are always valid.  This returns the blkg that it ended
  * up taking a reference on or %NULL if no reference was taken.
  */
 static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio,
         struct cgroup_subsys_state *css)
 {
     struct blkcg_gq *blkg, *ret_blkg = NULL;
 
     rcu_read_lock();
     blkg = blkg_lookup_create(css_to_blkcg(css),
                   bdev_get_queue(bio->bi_bdev));
     while (blkg) {
         if (blkg_tryget(blkg)) {
             ret_blkg = blkg;
             break;
         }
         blkg = blkg->parent;
     }
     rcu_read_unlock();
 
     return ret_blkg;
 }
 
 /**
  * bio_associate_blkg_from_css - associate a bio with a specified css
  * @bio: target bio
  * @css: target css
  *
  * Associate @bio with the blkg found by combining the css's blkg and the
  * request_queue of the @bio.  An association failure is handled by walking up
  * the blkg tree.  Therefore, the blkg associated can be anything between @blkg
  * and q->root_blkg.  This situation only happens when a cgroup is dying and
  * then the remaining bios will spill to the closest alive blkg.
  *
  * A reference will be taken on the blkg and will be released when @bio is
  * freed.
  */
 void bio_associate_blkg_from_css(struct bio *bio,
                  struct cgroup_subsys_state *css)
 {
     if (bio->bi_blkg)
         blkg_put(bio->bi_blkg);
 
     if (css && css->parent) {
         bio->bi_blkg = blkg_tryget_closest(bio, css);
     } else {
         blkg_get(bdev_get_queue(bio->bi_bdev)->root_blkg);
         bio->bi_blkg = bdev_get_queue(bio->bi_bdev)->root_blkg;
     }
 }
 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
 
 /**
  * bio_associate_blkg - associate a bio with a blkg
  * @bio: target bio
  *
  * Associate @bio with the blkg found from the bio's css and request_queue.
  * If one is not found, bio_lookup_blkg() creates the blkg.  If a blkg is
  * already associated, the css is reused and association redone as the
  * request_queue may have changed.
  */
 void bio_associate_blkg(struct bio *bio)
 {
     struct cgroup_subsys_state *css;
 
     rcu_read_lock();
 
     if (bio->bi_blkg)
         css = bio_blkcg_css(bio);
     else
         css = blkcg_css();
 
     bio_associate_blkg_from_css(bio, css);
 
     rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(bio_associate_blkg);
 
 /**
  * bio_clone_blkg_association - clone blkg association from src to dst bio
  * @dst: destination bio
  * @src: source bio
  */
 void bio_clone_blkg_association(struct bio *dst, struct bio *src)
 {
     if (src->bi_blkg)
         bio_associate_blkg_from_css(dst, bio_blkcg_css(src));
 }
 EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
 
 static int blk_cgroup_io_type(struct bio *bio)
 {
     if (op_is_discard(bio->bi_opf))
         return BLKG_IOSTAT_DISCARD;
     if (op_is_write(bio->bi_opf))
         return BLKG_IOSTAT_WRITE;
     return BLKG_IOSTAT_READ;
 }
 
 void blk_cgroup_bio_start(struct bio *bio)
 {
     int rwd = blk_cgroup_io_type(bio), cpu;
     struct blkg_iostat_set *bis;
     unsigned long flags;
 
     cpu = get_cpu();
     bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
     flags = u64_stats_update_begin_irqsave(&bis->sync);
 
     /*
      * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
      * bio and we would have already accounted for the size of the bio.
      */
     if (!bio_flagged(bio, BIO_CGROUP_ACCT)) {
         bio_set_flag(bio, BIO_CGROUP_ACCT);
         bis->cur.bytes[rwd] += bio->bi_iter.bi_size;
     }
     bis->cur.ios[rwd]++;
 
     u64_stats_update_end_irqrestore(&bis->sync, flags);
     if (cgroup_subsys_on_dfl(io_cgrp_subsys))
         cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
     put_cpu();
 }
 
 bool blk_cgroup_congested(void)
 {
     struct cgroup_subsys_state *css;
     bool ret = false;
 
     rcu_read_lock();
     for (css = blkcg_css(); css; css = css->parent) {
         if (atomic_read(&css->cgroup->congestion_count)) {
             ret = true;
             break;
         }
     }
     rcu_read_unlock();
     return ret;
 }
 
 static int __init blkcg_init(void)
 {
     blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
                         WQ_MEM_RECLAIM | WQ_FREEZABLE |
                         WQ_UNBOUND | WQ_SYSFS, 0);
     if (!blkcg_punt_bio_wq)
         return -ENOMEM;
     return 0;
 }
 subsys_initcall(blkcg_init);
 
 module_param(blkcg_debug_stats, bool, 0644);
 MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");

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