text: /*
   * 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/err.h>
  #include <linux/blkdev.h>
  #include <linux/backing-dev.h>
  #include <linux/slab.h>
  #include <linux/genhd.h>
  #include <linux/delay.h>
  #include <linux/atomic.h>
  #include <linux/ctype.h>
  #include <linux/blk-cgroup.h>
  #include "blk.h"
  
  #define MAX_KEY_LEN 100
  
  /*
   * 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;
  
  static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
  
  static LIST_HEAD(all_blkcgs);		/* protected by blkcg_pol_mutex */
  
  static bool blkcg_policy_enabled(struct request_queue *q,
  				 const struct blkcg_policy *pol)
  {
  	return pol && test_bit(pol->plid, q->blkcg_pols);
  }
  
  /**
   * blkg_free - free a blkg
   * @blkg: blkg to free
   *
   * Free @blkg which may be partially allocated.
   */
  static void blkg_free(struct blkcg_gq *blkg)
  {
  	int i;
  
  	if (!blkg)
  		return;
  
  	for (i = 0; i < BLKCG_MAX_POLS; i++)
  		if (blkg->pd[i])
  			blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
  
  	if (blkg->blkcg != &blkcg_root)
  		blk_exit_rl(&blkg->rl);
  
  	blkg_rwstat_exit(&blkg->stat_ios);
  	blkg_rwstat_exit(&blkg->stat_bytes);
  	kfree(blkg);
  }
  
  /**
   * 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;
  
  	/* alloc and init base part */
  	blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
  	if (!blkg)
  		return NULL;
  
  	if (blkg_rwstat_init(&blkg->stat_bytes, gfp_mask) ||
  	    blkg_rwstat_init(&blkg->stat_ios, gfp_mask))
  		goto err_free;
  
  	blkg->q = q;
  	INIT_LIST_HEAD(&blkg->q_node);
  	blkg->blkcg = blkcg;
  	atomic_set(&blkg->refcnt, 1);
  
  	/* root blkg uses @q->root_rl, init rl only for !root blkgs */
  	if (blkcg != &blkcg_root) {
  		if (blk_init_rl(&blkg->rl, q, gfp_mask))
  			goto err_free;
  		blkg->rl.blkg = blkg;
  	}
  
  	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->node);
  		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;
  	struct bdi_writeback_congested *wb_congested;
  	int i, ret;
  
  	WARN_ON_ONCE(!rcu_read_lock_held());
  	lockdep_assert_held(q->queue_lock);
  
  	/* blkg holds a reference to blkcg */
  	if (!css_tryget_online(&blkcg->css)) {
  		ret = -ENODEV;
  		goto err_free_blkg;
  	}
  
  	wb_congested = wb_congested_get_create(&q->backing_dev_info,
  					       blkcg->css.id, GFP_NOWAIT);
  	if (!wb_congested) {
  		ret = -ENOMEM;
  		goto err_put_css;
  	}
  
  	/* allocate */
  	if (!new_blkg) {
  		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT);
  		if (unlikely(!new_blkg)) {
  			ret = -ENOMEM;
  			goto err_put_congested;
  		}
  	}
  	blkg = new_blkg;
  	blkg->wb_congested = wb_congested;
  
  	/* 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_congested;
  		}
  		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_congested:
  	wb_congested_put(wb_congested);
  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 @q->queue_lock.
   *
   * Returns pointer to the looked up or created blkg on success, ERR_PTR()
   * value on error.  If @q is dead, returns ERR_PTR(-EINVAL).  If @q is not
   * dead and bypassing, returns ERR_PTR(-EBUSY).
   */
  struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
  				    struct request_queue *q)
  {
  	struct blkcg_gq *blkg;
  
  	WARN_ON_ONCE(!rcu_read_lock_held());
  	lockdep_assert_held(q->queue_lock);
  
  	/*
  	 * This could be the first entry point of blkcg implementation and
  	 * we shouldn't allow anything to go through for a bypassing queue.
  	 */
  	if (unlikely(blk_queue_bypass(q)))
  		return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY);
  
  	blkg = __blkg_lookup(blkcg, q, true);
  	if (blkg)
  		return blkg;
  
  	/*
  	 * 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 = blkcg_parent(blkcg);
  
  		while (parent && !__blkg_lookup(parent, q, false)) {
  			pos = parent;
  			parent = blkcg_parent(parent);
  		}
  
  		blkg = blkg_create(pos, q, NULL);
  		if (pos == blkcg || IS_ERR(blkg))
  			return blkg;
  	}
  }
  
  static void blkg_destroy(struct blkcg_gq *blkg)
  {
  	struct blkcg *blkcg = blkg->blkcg;
  	struct blkcg_gq *parent = blkg->parent;
  	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]);
  	}
  
  	if (parent) {
  		blkg_rwstat_add_aux(&parent->stat_bytes, &blkg->stat_bytes);
  		blkg_rwstat_add_aux(&parent->stat_ios, &blkg->stat_ios);
  	}
  
  	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.
  	 */
  	blkg_put(blkg);
  }
  
  /**
   * 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;
  
  	lockdep_assert_held(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);
  	}
  
  	q->root_blkg = NULL;
  	q->root_rl.blkg = NULL;
  }
  
  /*
   * 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.
   */
  void __blkg_release_rcu(struct rcu_head *rcu_head)
  {
  	struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head);
  
  	/* release the blkcg and parent blkg refs this blkg has been holding */
  	css_put(&blkg->blkcg->css);
  	if (blkg->parent)
  		blkg_put(blkg->parent);
  
  	wb_congested_put(blkg->wb_congested);
  
  	blkg_free(blkg);
  }
  EXPORT_SYMBOL_GPL(__blkg_release_rcu);
  
  /*
   * The next function used by blk_queue_for_each_rl().  It's a bit tricky
   * because the root blkg uses @q->root_rl instead of its own rl.
   */
  struct request_list *__blk_queue_next_rl(struct request_list *rl,
  					 struct request_queue *q)
  {
  	struct list_head *ent;
  	struct blkcg_gq *blkg;
  
  	/*
  	 * Determine the current blkg list_head.  The first entry is
  	 * root_rl which is off @q->blkg_list and mapped to the head.
  	 */
  	if (rl == &q->root_rl) {
  		ent = &q->blkg_list;
  		/* There are no more block groups, hence no request lists */
  		if (list_empty(ent))
  			return NULL;
  	} else {
  		blkg = container_of(rl, struct blkcg_gq, rl);
  		ent = &blkg->q_node;
  	}
  
  	/* walk to the next list_head, skip root blkcg */
  	ent = ent->next;
  	if (ent == &q->root_blkg->q_node)
  		ent = ent->next;
  	if (ent == &q->blkg_list)
  		return NULL;
  
  	blkg = container_of(ent, struct blkcg_gq, q_node);
  	return &blkg->rl;
  }
  
  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;
  
  	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) {
  		blkg_rwstat_reset(&blkg->stat_bytes);
  		blkg_rwstat_reset(&blkg->stat_ios);
  
  		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)
  {
  	/* some drivers (floppy) instantiate a queue w/o disk registered */
  	if (blkg->q->backing_dev_info.dev)
  		return dev_name(blkg->q->backing_dev_info.dev);
  	return NULL;
  }
  EXPORT_SYMBOL_GPL(blkg_dev_name);
  
  /**
   * 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);
  
  /**
   * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
   * @sf: seq_file to print to
   * @pd: policy private data of interest
   * @rwstat: rwstat to print
   *
   * Print @rwstat to @sf for the device assocaited with @pd.
   */
  u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
  			 const struct blkg_rwstat *rwstat)
  {
  	static const char *rwstr[] = {
  		[BLKG_RWSTAT_READ]	= "Read",
  		[BLKG_RWSTAT_WRITE]	= "Write",
  		[BLKG_RWSTAT_SYNC]	= "Sync",
  		[BLKG_RWSTAT_ASYNC]	= "Async",
  	};
  	const char *dname = blkg_dev_name(pd->blkg);
  	u64 v;
  	int i;
  
  	if (!dname)
  		return 0;
  
  	for (i = 0; i < BLKG_RWSTAT_NR; i++)
  		seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
  			   (unsigned long long)atomic64_read(&rwstat->aux_cnt[i]));
  
  	v = atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_READ]) +
  		atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_WRITE]);
  	seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
  	return v;
  }
  EXPORT_SYMBOL_GPL(__blkg_prfill_rwstat);
  
  /**
   * blkg_prfill_stat - prfill callback for blkg_stat
   * @sf: seq_file to print to
   * @pd: policy private data of interest
   * @off: offset to the blkg_stat in @pd
   *
   * prfill callback for printing a blkg_stat.
   */
  u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off)
  {
  	return __blkg_prfill_u64(sf, pd, blkg_stat_read((void *)pd + off));
  }
  EXPORT_SYMBOL_GPL(blkg_prfill_stat);
  
  /**
   * blkg_prfill_rwstat - prfill callback for blkg_rwstat
   * @sf: seq_file to print to
   * @pd: policy private data of interest
   * @off: offset to the blkg_rwstat in @pd
   *
   * prfill callback for printing a blkg_rwstat.
   */
  u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
  		       int off)
  {
  	struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
  
  	return __blkg_prfill_rwstat(sf, pd, &rwstat);
  }
  EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
  
  static u64 blkg_prfill_rwstat_field(struct seq_file *sf,
  				    struct blkg_policy_data *pd, int off)
  {
  	struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd->blkg + off);
  
  	return __blkg_prfill_rwstat(sf, pd, &rwstat);
  }
  
  /**
   * blkg_print_stat_bytes - seq_show callback for blkg->stat_bytes
   * @sf: seq_file to print to
   * @v: unused
   *
   * To be used as cftype->seq_show to print blkg->stat_bytes.
   * cftype->private must be set to the blkcg_policy.
   */
  int blkg_print_stat_bytes(struct seq_file *sf, void *v)
  {
  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
  			  blkg_prfill_rwstat_field, (void *)seq_cft(sf)->private,
  			  offsetof(struct blkcg_gq, stat_bytes), true);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blkg_print_stat_bytes);
  
  /**
   * blkg_print_stat_bytes - seq_show callback for blkg->stat_ios
   * @sf: seq_file to print to
   * @v: unused
   *
   * To be used as cftype->seq_show to print blkg->stat_ios.  cftype->private
   * must be set to the blkcg_policy.
   */
  int blkg_print_stat_ios(struct seq_file *sf, void *v)
  {
  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
  			  blkg_prfill_rwstat_field, (void *)seq_cft(sf)->private,
  			  offsetof(struct blkcg_gq, stat_ios), true);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blkg_print_stat_ios);
  
  static u64 blkg_prfill_rwstat_field_recursive(struct seq_file *sf,
  					      struct blkg_policy_data *pd,
  					      int off)
  {
  	struct blkg_rwstat rwstat = blkg_rwstat_recursive_sum(pd->blkg,
  							      NULL, off);
  	return __blkg_prfill_rwstat(sf, pd, &rwstat);
  }
  
  /**
   * blkg_print_stat_bytes_recursive - recursive version of blkg_print_stat_bytes
   * @sf: seq_file to print to
   * @v: unused
   */
  int blkg_print_stat_bytes_recursive(struct seq_file *sf, void *v)
  {
  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
  			  blkg_prfill_rwstat_field_recursive,
  			  (void *)seq_cft(sf)->private,
  			  offsetof(struct blkcg_gq, stat_bytes), true);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blkg_print_stat_bytes_recursive);
  
  /**
   * blkg_print_stat_ios_recursive - recursive version of blkg_print_stat_ios
   * @sf: seq_file to print to
   * @v: unused
   */
  int blkg_print_stat_ios_recursive(struct seq_file *sf, void *v)
  {
  	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
  			  blkg_prfill_rwstat_field_recursive,
  			  (void *)seq_cft(sf)->private,
  			  offsetof(struct blkcg_gq, stat_ios), true);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blkg_print_stat_ios_recursive);
  
  /**
   * blkg_stat_recursive_sum - collect hierarchical blkg_stat
   * @blkg: blkg of interest
   * @pol: blkcg_policy which contains the blkg_stat
   * @off: offset to the blkg_stat in blkg_policy_data or @blkg
   *
   * Collect the blkg_stat specified by @blkg, @pol and @off and all its
   * online descendants and their aux counts.  The caller must be holding the
   * queue lock for online tests.
   *
   * If @pol is NULL, blkg_stat is at @off bytes into @blkg; otherwise, it is
   * at @off bytes into @blkg's blkg_policy_data of the policy.
   */
  u64 blkg_stat_recursive_sum(struct blkcg_gq *blkg,
  			    struct blkcg_policy *pol, int off)
  {
  	struct blkcg_gq *pos_blkg;
  	struct cgroup_subsys_state *pos_css;
  	u64 sum = 0;
  
  	lockdep_assert_held(blkg->q->queue_lock);
  
  	rcu_read_lock();
  	blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
  		struct blkg_stat *stat;
  
  		if (!pos_blkg->online)
  			continue;
  
  		if (pol)
  			stat = (void *)blkg_to_pd(pos_blkg, pol) + off;
  		else
  			stat = (void *)blkg + off;
  
  		sum += blkg_stat_read(stat) + atomic64_read(&stat->aux_cnt);
  	}
  	rcu_read_unlock();
  
  	return sum;
  }
  EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
  
  /**
   * blkg_rwstat_recursive_sum - collect hierarchical blkg_rwstat
   * @blkg: blkg of interest
   * @pol: blkcg_policy which contains the blkg_rwstat
   * @off: offset to the blkg_rwstat in blkg_policy_data or @blkg
   *
   * Collect the blkg_rwstat specified by @blkg, @pol and @off and all its
   * online descendants and their aux counts.  The caller must be holding the
   * queue lock for online tests.
   *
   * If @pol is NULL, blkg_rwstat is at @off bytes into @blkg; otherwise, it
   * is at @off bytes into @blkg's blkg_policy_data of the policy.
   */
  struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
  					     struct blkcg_policy *pol, int off)
  {
  	struct blkcg_gq *pos_blkg;
  	struct cgroup_subsys_state *pos_css;
  	struct blkg_rwstat sum = { };
  	int i;
  
  	lockdep_assert_held(blkg->q->queue_lock);
  
  	rcu_read_lock();
  	blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
  		struct blkg_rwstat *rwstat;
  
  		if (!pos_blkg->online)
  			continue;
  
  		if (pol)
  			rwstat = (void *)blkg_to_pd(pos_blkg, pol) + off;
  		else
  			rwstat = (void *)pos_blkg + off;
  
  		for (i = 0; i < BLKG_RWSTAT_NR; i++)
  			atomic64_add(atomic64_read(&rwstat->aux_cnt[i]) +
  				percpu_counter_sum_positive(&rwstat->cpu_cnt[i]),
  				&sum.aux_cnt[i]);
  	}
  	rcu_read_unlock();
  
  	return sum;
  }
  EXPORT_SYMBOL_GPL(blkg_rwstat_recursive_sum);
  
  /**
   * 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(disk->queue->queue_lock)
  {
  	struct gendisk *disk;
  	struct blkcg_gq *blkg;
  	struct module *owner;
  	unsigned int major, minor;
  	int key_len, part, ret;
  	char *body;
  
  	if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
  		return -EINVAL;
  
  	body = input + key_len;
  	if (!isspace(*body))
  		return -EINVAL;
  	body = skip_spaces(body);
  
  	disk = get_gendisk(MKDEV(major, minor), &part);
  	if (!disk)
  		return -ENODEV;
  	if (part) {
  		owner = disk->fops->owner;
  		put_disk(disk);
  		module_put(owner);
  		return -ENODEV;
  	}
  
  	rcu_read_lock();
  	spin_lock_irq(disk->queue->queue_lock);
  
  	if (blkcg_policy_enabled(disk->queue, pol))
  		blkg = blkg_lookup_create(blkcg, disk->queue);
  	else
  		blkg = ERR_PTR(-EOPNOTSUPP);
  
  	if (IS_ERR(blkg)) {
  		ret = PTR_ERR(blkg);
  		rcu_read_unlock();
  		spin_unlock_irq(disk->queue->queue_lock);
  		owner = disk->fops->owner;
  		put_disk(disk);
  		module_put(owner);
  		/*
  		 * 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;
  	}
  
  	ctx->disk = disk;
  	ctx->blkg = blkg;
  	ctx->body = body;
  	return 0;
  }
  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->disk->queue->queue_lock) __releases(rcu)
  {
  	struct module *owner;
  
  	spin_unlock_irq(ctx->disk->queue->queue_lock);
  	rcu_read_unlock();
  	owner = ctx->disk->fops->owner;
  	put_disk(ctx->disk);
  	module_put(owner);
  }
  EXPORT_SYMBOL_GPL(blkg_conf_finish);
  
  static int blkcg_print_stat(struct seq_file *sf, void *v)
  {
  	struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
  	struct blkcg_gq *blkg;
  
  	rcu_read_lock();
  
  	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
  		const char *dname;
  		struct blkg_rwstat rwstat;
  		u64 rbytes, wbytes, rios, wios;
  
  		dname = blkg_dev_name(blkg);
  		if (!dname)
  			continue;
  
  		spin_lock_irq(blkg->q->queue_lock);
  
  		rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
  					offsetof(struct blkcg_gq, stat_bytes));
  		rbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
  		wbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
  
  		rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
  					offsetof(struct blkcg_gq, stat_ios));
  		rios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
  		wios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
  
  		spin_unlock_irq(blkg->q->queue_lock);
  
  		if (rbytes || wbytes || rios || wios)
  			seq_printf(sf, "%s rbytes=%llu wbytes=%llu rios=%llu wios=%llu\n",
  				   dname, rbytes, wbytes, rios, wios);
  	}
  
  	rcu_read_unlock();
  	return 0;
  }
  
  struct cftype blkcg_files[] = {
  	{
  		.name = "stat",
  		.flags = CFTYPE_NOT_ON_ROOT,
  		.seq_show = blkcg_print_stat,
  	},
  	{ }	/* terminate */
  };
  
  struct cftype blkcg_legacy_files[] = {
  	{
  		.name = "reset_stats",
  		.write_u64 = blkcg_reset_stats,
  	},
  	{ }	/* terminate */
  };
  
  /**
   * blkcg_css_offline - cgroup css_offline callback
   * @css: css of interest
   *
   * This function is called when @css is about to go away and responsible
   * for shooting down all blkgs associated with @css.  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.
   *
   * This is the blkcg counterpart of ioc_release_fn().
   */
  static void blkcg_css_offline(struct cgroup_subsys_state *css)
  {
  	struct blkcg *blkcg = css_to_blkcg(css);
  
  	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 (spin_trylock(q->queue_lock)) {
  			blkg_destroy(blkg);
  			spin_unlock(q->queue_lock);
  		} else {
  			spin_unlock_irq(&blkcg->lock);
  			cpu_relax();
  			spin_lock_irq(&blkcg->lock);
  		}
  	}
  
  	spin_unlock_irq(&blkcg->lock);
  
  	wb_blkcg_offline(blkcg);
  }
  
  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 free_blkcg;
  		}
  	}
  
  	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);
  	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT);
  	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]);
  free_blkcg:
  	kfree(blkcg);
  	mutex_unlock(&blkcg_pol_mutex);
  	return ret;
  }
  
  /**
   * blkcg_init_queue - initialize blkcg part of request queue
   * @q: request_queue to initialize
   *
   * Called from blk_alloc_queue_node(). 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;
  
  	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 and count the existing blkgs.  As
  	 * @q is bypassing at this point, blkg_lookup_create() can't be
  	 * used.  Open code insertion.
  	 */
  	rcu_read_lock();
  	spin_lock_irq(q->queue_lock);
  	blkg = blkg_create(&blkcg_root, q, new_blkg);
  	spin_unlock_irq(q->queue_lock);
  	rcu_read_unlock();
  
  	if (preloaded)
  		radix_tree_preload_end();
  
  	if (IS_ERR(blkg)) {
  		blkg_free(new_blkg);
  		return PTR_ERR(blkg);
  	}
  
  	q->root_blkg = blkg;
  	q->root_rl.blkg = blkg;
  
  	ret = blk_throtl_init(q);
  	if (ret) {
  		spin_lock_irq(q->queue_lock);
  		blkg_destroy_all(q);
  		spin_unlock_irq(q->queue_lock);
  	}
  	return ret;
  }
  
  /**
   * blkcg_drain_queue - drain blkcg part of request_queue
   * @q: request_queue to drain
   *
   * Called from blk_drain_queue().  Responsible for draining blkcg part.
   */
  void blkcg_drain_queue(struct request_queue *q)
  {
  	lockdep_assert_held(q->queue_lock);
  
  	/*
  	 * @q could be exiting and already have destroyed all blkgs as
  	 * indicated by NULL root_blkg.  If so, don't confuse policies.
  	 */
  	if (!q->root_blkg)
  		return;
  
  	blk_throtl_drain(q);
  }
  
  /**
   * blkcg_exit_queue - exit and release blkcg part of request_queue
   * @q: request_queue being released
   *
   * Called from blk_release_queue().  Responsible for exiting blkcg part.
   */
  void blkcg_exit_queue(struct request_queue *q)
  {
  	spin_lock_irq(q->queue_lock);
  	blkg_destroy_all(q);
  	spin_unlock_irq(q->queue_lock);
  
  	blk_throtl_exit(q);
  }
  
  /*
   * We cannot support shared io contexts, as we have no mean to support
   * two tasks with the same ioc in two different groups without major rework
   * of the main cic data structures.  For now we allow a task to change
   * its cgroup only if it's the only owner of its ioc.
   */
  static int blkcg_can_attach(struct cgroup_taskset *tset)
  {
  	struct task_struct *task;
  	struct cgroup_subsys_state *dst_css;
  	struct io_context *ioc;
  	int ret = 0;
  
  	/* task_lock() is needed to avoid races with exit_io_context() */
  	cgroup_taskset_for_each(task, dst_css, tset) {
  		task_lock(task);
  		ioc = task->io_context;
  		if (ioc && atomic_read(&ioc->nr_tasks) > 1)
  			ret = -EINVAL;
  		task_unlock(task);
  		if (ret)
  			break;
  	}
  	return ret;
  }
  
  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);
  }
  
  struct cgroup_subsys io_cgrp_subsys = {
  	.css_alloc = blkcg_css_alloc,
  	.css_offline = blkcg_css_offline,
  	.css_free = blkcg_css_free,
  	.can_attach = blkcg_can_attach,
  	.bind = blkcg_bind,
  	.dfl_cftypes = blkcg_files,
  	.legacy_cftypes = blkcg_legacy_files,
  	.legacy_name = "blkio",
  #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;
  	int ret;
  
  	if (blkcg_policy_enabled(q, pol))
  		return 0;
  
  	blk_queue_bypass_start(q);
  pd_prealloc:
  	if (!pd_prealloc) {
  		pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q->node);
  		if (!pd_prealloc) {
  			ret = -ENOMEM;
  			goto out_bypass_end;
  		}
  	}
  
  	spin_lock_irq(q->queue_lock);
  
  	list_for_each_entry(blkg, &q->blkg_list, q_node) {
  		struct blkg_policy_data *pd;
  
  		if (blkg->pd[pol->plid])
  			continue;
  
  		pd = pol->pd_alloc_fn(GFP_NOWAIT, q->node);
  		if (!pd)
  			swap(pd, pd_prealloc);
  		if (!pd) {
  			spin_unlock_irq(q->queue_lock);
  			goto pd_prealloc;
  		}
  
  		blkg->pd[pol->plid] = pd;
  		pd->blkg = blkg;
  		pd->plid = pol->plid;
  		if (pol->pd_init_fn)
  			pol->pd_init_fn(pd);
  	}
  
  	__set_bit(pol->plid, q->blkcg_pols);
  	ret = 0;
  
  	spin_unlock_irq(q->queue_lock);
  out_bypass_end:
  	blk_queue_bypass_end(q);
  	if (pd_prealloc)
  		pol->pd_free_fn(pd_prealloc);
  	return ret;
  }
  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;
  
  	blk_queue_bypass_start(q);
  	spin_lock_irq(q->queue_lock);
  
  	__clear_bit(pol->plid, q->blkcg_pols);
  
  	list_for_each_entry(blkg, &q->blkg_list, q_node) {
  		/* grab blkcg lock too while removing @pd from @blkg */
  		spin_lock(&blkg->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(&blkg->blkcg->lock);
  	}
  
  	spin_unlock_irq(q->queue_lock);
  	blk_queue_bypass_end(q);
  }
  EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
  
  /**
   * 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)
  		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) {
  				mutex_unlock(&blkcg_pol_mutex);
  				goto err_free_cpds;
  			}
  
  			blkcg->cpd[pol->plid] = cpd;
  			cpd->blkcg = blkcg;
  			cpd->plid = pol->plid;
  			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_alloc_fn) {
  		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[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)
  {
  	struct blkcg *blkcg;
  
  	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_alloc_fn) {
  		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[pol->plid] = NULL;
  
  	mutex_unlock(&blkcg_pol_mutex);
  out_unlock:
  	mutex_unlock(&blkcg_pol_register_mutex);
  }
  EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
  