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/*
* 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>
*/
#include <linux/ioprio.h>
#include <linux/kdev_t.h>
#include <linux/module.h>
#include <linux/err.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/genhd.h>
#include <linux/delay.h>
#include <linux/atomic.h>
#include "blk-cgroup.h"
#include "blk.h"

#define MAX_KEY_LEN 100

static DEFINE_MUTEX(blkcg_pol_mutex);

struct blkcg blkcg_root = { .cfq_weight = 2 * CFQ_WEIGHT_DEFAULT };
EXPORT_SYMBOL_GPL(blkcg_root);

static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];

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++) {
struct blkcg_policy *pol = blkcg_policy[i];
struct blkg_policy_data *pd = blkg->pd[i];

if (!pd)
continue;

if (pol && pol->pd_exit_fn)
pol->pd_exit_fn(blkg);

kfree(pd);
}

blk_exit_rl(&blkg->rl);
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;

blkg->q = q;
INIT_LIST_HEAD(&blkg->q_node);
blkg->blkcg = blkcg;
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 = kzalloc_node(pol->pd_size, gfp_mask, q->node);
if (!pd)
goto err_free;

blkg->pd[i] = pd;
pd->blkg = blkg;

/* invoke per-policy init */
if (blkcg_policy_enabled(blkg->q, pol))
pol->pd_init_fn(blkg);
}

return blkg;

err_free:
blkg_free(blkg);
return NULL;
}

static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
struct request_queue *q)
{
struct blkcg_gq *blkg;

blkg = rcu_dereference(blkcg->blkg_hint);
if (blkg && blkg->q == q)
return blkg;

/*
* Hint didn't match. Look up from the radix tree. Note that we
* may not be holding queue_lock and thus are not sure whether
* @blkg from blkg_tree has already been removed or not, so we
* can't update hint to the lookup result. Leave it to the caller.
*/
blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
if (blkg && blkg->q == q)
return blkg;

return NULL;
}

/**
* blkg_lookup - lookup blkg for the specified blkcg - q pair
* @blkcg: blkcg of interest
* @q: request_queue of interest
*
* Lookup blkg for the @blkcg - @q pair. This function should be called
* under RCU read lock and is guaranteed to return %NULL if @q is bypassing
* - see blk_queue_bypass_start() for details.
*/
struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
{
WARN_ON_ONCE(!rcu_read_lock_held());

if (unlikely(blk_queue_bypass(q)))
return NULL;
return __blkg_lookup(blkcg, q);
}
EXPORT_SYMBOL_GPL(blkg_lookup);

/*
* If @new_blkg is %NULL, this function tries to allocate a new one as
* necessary using %GFP_ATOMIC. @new_blkg is always consumed on return.
*/
static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q,
struct blkcg_gq *new_blkg)
{
struct blkcg_gq *blkg;
int ret;

WARN_ON_ONCE(!rcu_read_lock_held());
lockdep_assert_held(q->queue_lock);

/* lookup and update hint on success, see __blkg_lookup() for details */
blkg = __blkg_lookup(blkcg, q);
if (blkg) {
rcu_assign_pointer(blkcg->blkg_hint, blkg);
goto out_free;
}

/* blkg holds a reference to blkcg */
if (!css_tryget(&blkcg->css)) {
blkg = ERR_PTR(-EINVAL);
goto out_free;
}

/* allocate */
if (!new_blkg) {
new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
if (unlikely(!new_blkg)) {
blkg = ERR_PTR(-ENOMEM);
goto out_put;
}
}
blkg = new_blkg;

/* 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);
}
spin_unlock(&blkcg->lock);

if (!ret)
return blkg;

blkg = ERR_PTR(ret);
out_put:
css_put(&blkcg->css);
out_free:
blkg_free(new_blkg);
return blkg;
}

struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
{
/*
* 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_dead(q) ? -EINVAL : -EBUSY);
return __blkg_lookup_create(blkcg, q, NULL);
}
EXPORT_SYMBOL_GPL(blkg_lookup_create);

static void blkg_destroy(struct blkcg_gq *blkg)
{
struct blkcg *blkcg = blkg->blkcg;

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));

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_dereference_raw(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);
}
}

static void blkg_rcu_free(struct rcu_head *rcu_head)
{
blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
}

void __blkg_release(struct blkcg_gq *blkg)
{
/* release the extra blkcg reference this blkg has been holding */
css_put(&blkg->blkcg->css);

/*
* A group is freed in rcu manner. 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 acess to only
* values local to groups like group stats and group rate limits
*/
call_rcu(&blkg->rcu_head, blkg_rcu_free);
}
EXPORT_SYMBOL_GPL(__blkg_release);

/*
* 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;
} 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 *cgroup, struct cftype *cftype,
u64 val)
{
struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
struct blkcg_gq *blkg;
struct hlist_node *n;
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, n, &blkcg->blkg_list, blkcg_node) {
for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];

if (blkcg_policy_enabled(blkg->q, pol) &&
pol->pd_reset_stats_fn)
pol->pd_reset_stats_fn(blkg);
}
}

spin_unlock_irq(&blkcg->lock);
mutex_unlock(&blkcg_pol_mutex);
return 0;
}

static 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;
}

/**
* 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. 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;
struct hlist_node *n;
u64 total = 0;

spin_lock_irq(&blkcg->lock);
hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
if (blkcg_policy_enabled(blkg->q, pol))
total += prfill(sf, blkg->pd[pol->plid], data);
spin_unlock_irq(&blkcg->lock);

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)rwstat->cnt[i]);

v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
return v;
}

/**
* 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);

/**
* 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->v the new
* value. 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,
const char *input, struct blkg_conf_ctx *ctx)
__acquires(rcu) __acquires(disk->queue->queue_lock)
{
struct gendisk *disk;
struct blkcg_gq *blkg;
unsigned int major, minor;
unsigned long long v;
int part, ret;

if (sscanf(input, "%u:%u %llu", &major, &minor, &v) != 3)
return -EINVAL;

disk = get_gendisk(MKDEV(major, minor), &part);
if (!disk || part)
return -EINVAL;

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(-EINVAL);

if (IS_ERR(blkg)) {
ret = PTR_ERR(blkg);
rcu_read_unlock();
spin_unlock_irq(disk->queue->queue_lock);
put_disk(disk);
/*
* 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->v = v;
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)
{
spin_unlock_irq(ctx->disk->queue->queue_lock);
rcu_read_unlock();
put_disk(ctx->disk);
}
EXPORT_SYMBOL_GPL(blkg_conf_finish);

struct cftype blkcg_files[] = {
{
.name = "reset_stats",
.write_u64 = blkcg_reset_stats,
},
{ } /* terminate */
};

/**
* blkcg_pre_destroy - cgroup pre_destroy callback
* @cgroup: cgroup of interest
*
* This function is called when @cgroup is about to go away and responsible
* for shooting down all blkgs associated with @cgroup. 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 int blkcg_pre_destroy(struct cgroup *cgroup)
{
struct blkcg *blkcg = cgroup_to_blkcg(cgroup);

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);
return 0;
}

static void blkcg_destroy(struct cgroup *cgroup)
{
struct blkcg *blkcg = cgroup_to_blkcg(cgroup);

if (blkcg != &blkcg_root)
kfree(blkcg);
}

static struct cgroup_subsys_state *blkcg_create(struct cgroup *cgroup)
{
static atomic64_t id_seq = ATOMIC64_INIT(0);
struct blkcg *blkcg;
struct cgroup *parent = cgroup->parent;

if (!parent) {
blkcg = &blkcg_root;
goto done;
}

blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
if (!blkcg)
return ERR_PTR(-ENOMEM);

blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
done:
spin_lock_init(&blkcg->lock);
INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
INIT_HLIST_HEAD(&blkcg->blkg_list);

return &blkcg->css;
}

/**
* 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)
{
might_sleep();

return blk_throtl_init(q);
}

/**
* 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);

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 *cgrp, struct cgroup_taskset *tset)
{
struct task_struct *task;
struct io_context *ioc;
int ret = 0;

/* task_lock() is needed to avoid races with exit_io_context() */
cgroup_taskset_for_each(task, cgrp, 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;
}

struct cgroup_subsys blkio_subsys = {
.name = "blkio",
.create = blkcg_create,
.can_attach = blkcg_can_attach,
.pre_destroy = blkcg_pre_destroy,
.destroy = blkcg_destroy,
.subsys_id = blkio_subsys_id,
.base_cftypes = blkcg_files,
.module = THIS_MODULE,
};
EXPORT_SYMBOL_GPL(blkio_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)
{
LIST_HEAD(pds);
struct blkcg_gq *blkg;
struct blkg_policy_data *pd, *n;
int cnt = 0, ret;
bool preloaded;

if (blkcg_policy_enabled(q, pol))
return 0;

/* preallocations for root blkg */
blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
if (!blkg)
return -ENOMEM;

preloaded = !radix_tree_preload(GFP_KERNEL);

blk_queue_bypass_start(q);

/* make sure the root blkg exists and count the existing blkgs */
spin_lock_irq(q->queue_lock);

rcu_read_lock();
blkg = __blkg_lookup_create(&blkcg_root, q, blkg);
rcu_read_unlock();

if (preloaded)
radix_tree_preload_end();

if (IS_ERR(blkg)) {
ret = PTR_ERR(blkg);
goto out_unlock;
}
q->root_blkg = blkg;
q->root_rl.blkg = blkg;

list_for_each_entry(blkg, &q->blkg_list, q_node)
cnt++;

spin_unlock_irq(q->queue_lock);

/* allocate policy_data for all existing blkgs */
while (cnt--) {
pd = kzalloc_node(pol->pd_size, GFP_KERNEL, q->node);
if (!pd) {
ret = -ENOMEM;
goto out_free;
}
list_add_tail(&pd->alloc_node, &pds);
}

/*
* Install the allocated pds. With @q bypassing, no new blkg
* should have been created while the queue lock was dropped.
*/
spin_lock_irq(q->queue_lock);

list_for_each_entry(blkg, &q->blkg_list, q_node) {
if (WARN_ON(list_empty(&pds))) {
/* umm... this shouldn't happen, just abort */
ret = -ENOMEM;
goto out_unlock;
}
pd = list_first_entry(&pds, struct blkg_policy_data, alloc_node);
list_del_init(&pd->alloc_node);

/* grab blkcg lock too while installing @pd on @blkg */
spin_lock(&blkg->blkcg->lock);

blkg->pd[pol->plid] = pd;
pd->blkg = blkg;
pol->pd_init_fn(blkg);

spin_unlock(&blkg->blkcg->lock);
}

__set_bit(pol->plid, q->blkcg_pols);
ret = 0;
out_unlock:
spin_unlock_irq(q->queue_lock);
out_free:
blk_queue_bypass_end(q);
list_for_each_entry_safe(pd, n, &pds, alloc_node)
kfree(pd);
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);

/* if no policy is left, no need for blkgs - shoot them down */
if (bitmap_empty(q->blkcg_pols, BLKCG_MAX_POLS))
blkg_destroy_all(q);

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 (pol->pd_exit_fn)
pol->pd_exit_fn(blkg);

kfree(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)
{
int i, ret;

if (WARN_ON(pol->pd_size < sizeof(struct blkg_policy_data)))
return -EINVAL;

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 out_unlock;

/* register and update blkgs */
pol->plid = i;
blkcg_policy[i] = pol;

/* everything is in place, add intf files for the new policy */
if (pol->cftypes)
WARN_ON(cgroup_add_cftypes(&blkio_subsys, pol->cftypes));
ret = 0;
out_unlock:
mutex_unlock(&blkcg_pol_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_mutex);

if (WARN_ON(blkcg_policy[pol->plid] != pol))
goto out_unlock;

/* kill the intf files first */
if (pol->cftypes)
cgroup_rm_cftypes(&blkio_subsys, pol->cftypes);

/* unregister and update blkgs */
blkcg_policy[pol->plid] = NULL;
out_unlock:
mutex_unlock(&blkcg_pol_mutex);
}
EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
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