Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2020 insertions, 0 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
new file mode 100644
index 000000000..1b7fd1fc2
--- /dev/null
+++ b/block/blk-cgroup.c
@@ -0,0 +1,2020 @@
+// 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"
+#include "blk-rq-qos.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
+ * @disk: gendisk 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 gendisk *disk,
+				   gfp_t gfp_mask)
+{
+	struct blkcg_gq *blkg;
+	int i, cpu;
+
+	/* alloc and init base part */
+	blkg = kzalloc_node(sizeof(*blkg), gfp_mask, disk->queue->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(disk->queue))
+		goto err_free;
+
+	blkg->q = disk->queue;
+	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(disk->queue, pol))
+			continue;
+
+		/* alloc per-policy data and attach it to blkg */
+		pd = pol->pd_alloc_fn(gfp_mask, disk->queue, 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;
+}
+
+/*
+ * 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 gendisk *disk,
+				    struct blkcg_gq *new_blkg)
+{
+	struct blkcg_gq *blkg;
+	int i, ret;
+
+	lockdep_assert_held(&disk->queue->queue_lock);
+
+	/* request_queue is dying, do not create/recreate a blkg */
+	if (blk_queue_dying(disk->queue)) {
+		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, disk, 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), disk->queue);
+		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, disk->queue->id, blkg);
+	if (likely(!ret)) {
+		hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
+		list_add(&blkg->q_node, &disk->queue->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
+ * @disk: gendisk of interest
+ *
+ * Lookup blkg for the @blkcg - @disk 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 @disk->queue->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 gendisk *disk)
+{
+	struct request_queue *q = disk->queue;
+	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);
+	if (blkg) {
+		if (blkcg != &blkcg_root &&
+		    blkg != rcu_dereference(blkcg->blkg_hint))
+			rcu_assign_pointer(blkcg->blkg_hint, 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);
+			if (blkg) {
+				/* remember closest blkg */
+				ret_blkg = blkg;
+				break;
+			}
+			pos = parent;
+			parent = blkcg_parent(parent);
+		}
+
+		blkg = blkg_create(pos, disk, 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);
+}
+
+static void blkg_destroy_all(struct gendisk *disk)
+{
+	struct request_queue *q = disk->queue;
+	struct blkcg_gq *blkg, *n;
+	int count = BLKG_DESTROY_BATCH_SIZE;
+	int i;
+
+restart:
+	spin_lock_irq(&q->queue_lock);
+	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
+		struct blkcg *blkcg = blkg->blkcg;
+
+		if (hlist_unhashed(&blkg->blkcg_node))
+			continue;
+
+		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;
+		}
+	}
+
+	/*
+	 * Mark policy deactivated since policy offline has been done, and
+	 * the free is scheduled, so future blkcg_deactivate_policy() can
+	 * be bypassed
+	 */
+	for (i = 0; i < BLKCG_MAX_POLS; i++) {
+		struct blkcg_policy *pol = blkcg_policy[i];
+
+		if (pol)
+			__clear_bit(pol->plid, q->blkcg_pols);
+	}
+
+	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);
+
+/**
+ * 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 gendisk *disk;
+	struct request_queue *q;
+	struct blkcg_gq *blkg;
+	int ret;
+
+	bdev = blkcg_conf_open_bdev(&input);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+	disk = bdev->bd_disk;
+	q = disk->queue;
+
+	/*
+	 * 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);
+
+	if (!blkcg_policy_enabled(q, pol)) {
+		ret = -EOPNOTSUPP;
+		goto fail_unlock;
+	}
+
+	blkg = blkg_lookup(blkcg, q);
+	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)) {
+			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, disk, 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);
+
+		if (!blkcg_policy_enabled(q, pol)) {
+			blkg_free(new_blkg);
+			ret = -EOPNOTSUPP;
+			goto fail_preloaded;
+		}
+
+		blkg = blkg_lookup(pos, q);
+		if (blkg) {
+			blkg_free(new_blkg);
+		} else {
+			blkg = blkg_create(pos, disk, 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 = bdev->bd_disk->queue->root_blkg;
+		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(&parent->css);
+	return 0;
+}
+
+int blkcg_init_disk(struct gendisk *disk)
+{
+	struct request_queue *q = disk->queue;
+	struct blkcg_gq *new_blkg, *blkg;
+	bool preloaded;
+	int ret;
+
+	INIT_LIST_HEAD(&q->blkg_list);
+
+	new_blkg = blkg_alloc(&blkcg_root, disk, 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, disk, 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(disk);
+	if (ret)
+		goto err_destroy_all;
+
+	ret = blk_throtl_init(disk);
+	if (ret)
+		goto err_ioprio_exit;
+
+	ret = blk_iolatency_init(disk);
+	if (ret)
+		goto err_throtl_exit;
+
+	return 0;
+
+err_throtl_exit:
+	blk_throtl_exit(disk);
+err_ioprio_exit:
+	blk_ioprio_exit(disk);
+err_destroy_all:
+	blkg_destroy_all(disk);
+	return ret;
+err_unlock:
+	spin_unlock_irq(&q->queue_lock);
+	if (preloaded)
+		radix_tree_preload_end();
+	return PTR_ERR(blkg);
+}
+
+void blkcg_exit_disk(struct gendisk *disk)
+{
+	blkg_destroy_all(disk);
+	rq_qos_exit(disk->queue);
+	blk_throtl_exit(disk);
+}
+
+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]);
+
+	if (pol->pd_online_fn)
+		list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
+			pol->pd_online_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
+ * @gendisk: disk to throttle
+ * @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 block_device 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 gendisk *disk, bool use_memdelay)
+{
+	struct request_queue *q = disk->queue;
+
+	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), bio->bi_bdev->bd_disk);
+	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");