blkcg: restructure statistics printing

[mirror_ubuntu-artful-kernel.git] / block / blk-cgroup.c

/*
 * 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/seq_file.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_SPINLOCK(blkio_list_lock);
static LIST_HEAD(blkio_list);

static DEFINE_MUTEX(all_q_mutex);
static LIST_HEAD(all_q_list);

/* List of groups pending per cpu stats allocation */
static DEFINE_SPINLOCK(alloc_list_lock);
static LIST_HEAD(alloc_list);

static void blkio_stat_alloc_fn(struct work_struct *);
static DECLARE_DELAYED_WORK(blkio_stat_alloc_work, blkio_stat_alloc_fn);

struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
EXPORT_SYMBOL_GPL(blkio_root_cgroup);

static struct blkio_policy_type *blkio_policy[BLKIO_NR_POLICIES];

/* for encoding cft->private value on file */
#define BLKIOFILE_PRIVATE(x, val)       (((x) << 16) | (val))
/* What policy owns the file, proportional or throttle */
#define BLKIOFILE_POLICY(val)           (((val) >> 16) & 0xffff)
#define BLKIOFILE_ATTR(val)             ((val) & 0xffff)

struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
{
        return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
                            struct blkio_cgroup, css);
}
EXPORT_SYMBOL_GPL(cgroup_to_blkio_cgroup);

static struct blkio_cgroup *task_blkio_cgroup(struct task_struct *tsk)
{
        return container_of(task_subsys_state(tsk, blkio_subsys_id),
                            struct blkio_cgroup, css);
}

struct blkio_cgroup *bio_blkio_cgroup(struct bio *bio)
{
        if (bio && bio->bi_css)
                return container_of(bio->bi_css, struct blkio_cgroup, css);
        return task_blkio_cgroup(current);
}
EXPORT_SYMBOL_GPL(bio_blkio_cgroup);

static inline void blkio_update_group_weight(struct blkio_group *blkg,
                                             int plid, unsigned int weight)
{
        struct blkio_policy_type *blkiop;

        list_for_each_entry(blkiop, &blkio_list, list) {
                /* If this policy does not own the blkg, do not send updates */
                if (blkiop->plid != plid)
                        continue;
                if (blkiop->ops.blkio_update_group_weight_fn)
                        blkiop->ops.blkio_update_group_weight_fn(blkg->q,
                                                        blkg, weight);
        }
}

static inline void blkio_update_group_bps(struct blkio_group *blkg, int plid,
                                          u64 bps, int fileid)
{
        struct blkio_policy_type *blkiop;

        list_for_each_entry(blkiop, &blkio_list, list) {

                /* If this policy does not own the blkg, do not send updates */
                if (blkiop->plid != plid)
                        continue;

                if (fileid == BLKIO_THROTL_read_bps_device
                    && blkiop->ops.blkio_update_group_read_bps_fn)
                        blkiop->ops.blkio_update_group_read_bps_fn(blkg->q,
                                                                blkg, bps);

                if (fileid == BLKIO_THROTL_write_bps_device
                    && blkiop->ops.blkio_update_group_write_bps_fn)
                        blkiop->ops.blkio_update_group_write_bps_fn(blkg->q,
                                                                blkg, bps);
        }
}

static inline void blkio_update_group_iops(struct blkio_group *blkg,
                                           int plid, unsigned int iops,
                                           int fileid)
{
        struct blkio_policy_type *blkiop;

        list_for_each_entry(blkiop, &blkio_list, list) {

                /* If this policy does not own the blkg, do not send updates */
                if (blkiop->plid != plid)
                        continue;

                if (fileid == BLKIO_THROTL_read_iops_device
                    && blkiop->ops.blkio_update_group_read_iops_fn)
                        blkiop->ops.blkio_update_group_read_iops_fn(blkg->q,
                                                                blkg, iops);

                if (fileid == BLKIO_THROTL_write_iops_device
                    && blkiop->ops.blkio_update_group_write_iops_fn)
                        blkiop->ops.blkio_update_group_write_iops_fn(blkg->q,
                                                                blkg,iops);
        }
}

#ifdef CONFIG_DEBUG_BLK_CGROUP
/* This should be called with the queue_lock held. */
static void blkio_set_start_group_wait_time(struct blkio_group *blkg,
                                            struct blkio_policy_type *pol,
                                            struct blkio_group *curr_blkg)
{
        struct blkg_policy_data *pd = blkg->pd[pol->plid];

        if (blkio_blkg_waiting(&pd->stats))
                return;
        if (blkg == curr_blkg)
                return;
        pd->stats.start_group_wait_time = sched_clock();
        blkio_mark_blkg_waiting(&pd->stats);
}

/* This should be called with the queue_lock held. */
static void blkio_update_group_wait_time(struct blkio_group_stats *stats)
{
        unsigned long long now;

        if (!blkio_blkg_waiting(stats))
                return;

        now = sched_clock();
        if (time_after64(now, stats->start_group_wait_time))
                blkg_stat_add(&stats->group_wait_time,
                              now - stats->start_group_wait_time);
        blkio_clear_blkg_waiting(stats);
}

/* This should be called with the queue_lock held. */
static void blkio_end_empty_time(struct blkio_group_stats *stats)
{
        unsigned long long now;

        if (!blkio_blkg_empty(stats))
                return;

        now = sched_clock();
        if (time_after64(now, stats->start_empty_time))
                blkg_stat_add(&stats->empty_time,
                              now - stats->start_empty_time);
        blkio_clear_blkg_empty(stats);
}

void blkiocg_update_set_idle_time_stats(struct blkio_group *blkg,
                                        struct blkio_policy_type *pol)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

        lockdep_assert_held(blkg->q->queue_lock);
        BUG_ON(blkio_blkg_idling(stats));

        stats->start_idle_time = sched_clock();
        blkio_mark_blkg_idling(stats);
}
EXPORT_SYMBOL_GPL(blkiocg_update_set_idle_time_stats);

void blkiocg_update_idle_time_stats(struct blkio_group *blkg,
                                    struct blkio_policy_type *pol)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

        lockdep_assert_held(blkg->q->queue_lock);

        if (blkio_blkg_idling(stats)) {
                unsigned long long now = sched_clock();

                if (time_after64(now, stats->start_idle_time))
                        blkg_stat_add(&stats->idle_time,
                                      now - stats->start_idle_time);
                blkio_clear_blkg_idling(stats);
        }
}
EXPORT_SYMBOL_GPL(blkiocg_update_idle_time_stats);

void blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg,
                                         struct blkio_policy_type *pol)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_stat_add(&stats->avg_queue_size_sum,
                      blkg_rwstat_sum(&stats->queued));
        blkg_stat_add(&stats->avg_queue_size_samples, 1);
        blkio_update_group_wait_time(stats);
}
EXPORT_SYMBOL_GPL(blkiocg_update_avg_queue_size_stats);

void blkiocg_set_start_empty_time(struct blkio_group *blkg,
                                  struct blkio_policy_type *pol)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

        lockdep_assert_held(blkg->q->queue_lock);

        if (blkg_rwstat_sum(&stats->queued))
                return;

        /*
         * group is already marked empty. This can happen if cfqq got new
         * request in parent group and moved to this group while being added
         * to service tree. Just ignore the event and move on.
         */
        if (blkio_blkg_empty(stats))
                return;

        stats->start_empty_time = sched_clock();
        blkio_mark_blkg_empty(stats);
}
EXPORT_SYMBOL_GPL(blkiocg_set_start_empty_time);

void blkiocg_update_dequeue_stats(struct blkio_group *blkg,
                                  struct blkio_policy_type *pol,
                                  unsigned long dequeue)
{
        struct blkg_policy_data *pd = blkg->pd[pol->plid];

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_stat_add(&pd->stats.dequeue, dequeue);
}
EXPORT_SYMBOL_GPL(blkiocg_update_dequeue_stats);
#else
static inline void blkio_set_start_group_wait_time(struct blkio_group *blkg,
                                        struct blkio_policy_type *pol,
                                        struct blkio_group *curr_blkg) { }
static inline void blkio_end_empty_time(struct blkio_group_stats *stats) { }
#endif

void blkiocg_update_io_add_stats(struct blkio_group *blkg,
                                 struct blkio_policy_type *pol,
                                 struct blkio_group *curr_blkg, bool direction,
                                 bool sync)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
        int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_rwstat_add(&stats->queued, rw, 1);
        blkio_end_empty_time(stats);
        blkio_set_start_group_wait_time(blkg, pol, curr_blkg);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_add_stats);

void blkiocg_update_io_remove_stats(struct blkio_group *blkg,
                                    struct blkio_policy_type *pol,
                                    bool direction, bool sync)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
        int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_rwstat_add(&stats->queued, rw, -1);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_remove_stats);

void blkiocg_update_timeslice_used(struct blkio_group *blkg,
                                   struct blkio_policy_type *pol,
                                   unsigned long time,
                                   unsigned long unaccounted_time)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_stat_add(&stats->time, time);
#ifdef CONFIG_DEBUG_BLK_CGROUP
        blkg_stat_add(&stats->unaccounted_time, unaccounted_time);
#endif
}
EXPORT_SYMBOL_GPL(blkiocg_update_timeslice_used);

/*
 * should be called under rcu read lock or queue lock to make sure blkg pointer
 * is valid.
 */
void blkiocg_update_dispatch_stats(struct blkio_group *blkg,
                                   struct blkio_policy_type *pol,
                                   uint64_t bytes, bool direction, bool sync)
{
        int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);
        struct blkg_policy_data *pd = blkg->pd[pol->plid];
        struct blkio_group_stats_cpu *stats_cpu;
        unsigned long flags;

        /* If per cpu stats are not allocated yet, don't do any accounting. */
        if (pd->stats_cpu == NULL)
                return;

        /*
         * Disabling interrupts to provide mutual exclusion between two
         * writes on same cpu. It probably is not needed for 64bit. Not
         * optimizing that case yet.
         */
        local_irq_save(flags);

        stats_cpu = this_cpu_ptr(pd->stats_cpu);

        blkg_stat_add(&stats_cpu->sectors, bytes >> 9);
        blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
        blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);

        local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(blkiocg_update_dispatch_stats);

void blkiocg_update_completion_stats(struct blkio_group *blkg,
                                     struct blkio_policy_type *pol,
                                     uint64_t start_time,
                                     uint64_t io_start_time, bool direction,
                                     bool sync)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
        unsigned long long now = sched_clock();
        int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);

        lockdep_assert_held(blkg->q->queue_lock);

        if (time_after64(now, io_start_time))
                blkg_rwstat_add(&stats->service_time, rw, now - io_start_time);
        if (time_after64(io_start_time, start_time))
                blkg_rwstat_add(&stats->wait_time, rw,
                                io_start_time - start_time);
}
EXPORT_SYMBOL_GPL(blkiocg_update_completion_stats);

/*  Merged stats are per cpu.  */
void blkiocg_update_io_merged_stats(struct blkio_group *blkg,
                                    struct blkio_policy_type *pol,
                                    bool direction, bool sync)
{
        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
        int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);

        lockdep_assert_held(blkg->q->queue_lock);

        blkg_rwstat_add(&stats->merged, rw, 1);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);

/*
 * Worker for allocating per cpu stat for blk groups. This is scheduled on
 * the system_nrt_wq once there are some groups on the alloc_list waiting
 * for allocation.
 */
static void blkio_stat_alloc_fn(struct work_struct *work)
{
        static void *pcpu_stats[BLKIO_NR_POLICIES];
        struct delayed_work *dwork = to_delayed_work(work);
        struct blkio_group *blkg;
        int i;
        bool empty = false;

alloc_stats:
        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
                if (pcpu_stats[i] != NULL)
                        continue;

                pcpu_stats[i] = alloc_percpu(struct blkio_group_stats_cpu);

                /* Allocation failed. Try again after some time. */
                if (pcpu_stats[i] == NULL) {
                        queue_delayed_work(system_nrt_wq, dwork,
                                                msecs_to_jiffies(10));
                        return;
                }
        }

        spin_lock_irq(&blkio_list_lock);
        spin_lock(&alloc_list_lock);

        /* cgroup got deleted or queue exited. */
        if (!list_empty(&alloc_list)) {
                blkg = list_first_entry(&alloc_list, struct blkio_group,
                                                alloc_node);
                for (i = 0; i < BLKIO_NR_POLICIES; i++) {
                        struct blkg_policy_data *pd = blkg->pd[i];

                        if (blkio_policy[i] && pd && !pd->stats_cpu)
                                swap(pd->stats_cpu, pcpu_stats[i]);
                }

                list_del_init(&blkg->alloc_node);
        }

        empty = list_empty(&alloc_list);

        spin_unlock(&alloc_list_lock);
        spin_unlock_irq(&blkio_list_lock);

        if (!empty)
                goto alloc_stats;
}

/**
 * blkg_free - free a blkg
 * @blkg: blkg to free
 *
 * Free @blkg which may be partially allocated.
 */
static void blkg_free(struct blkio_group *blkg)
{
        int i;

        if (!blkg)
                return;

        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
                struct blkg_policy_data *pd = blkg->pd[i];

                if (pd) {
                        free_percpu(pd->stats_cpu);
                        kfree(pd);
                }
        }

        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
 *
 * Allocate a new blkg assocating @blkcg and @q.
 */
static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
                                      struct request_queue *q)
{
        struct blkio_group *blkg;
        int i;

        /* alloc and init base part */
        blkg = kzalloc_node(sizeof(*blkg), GFP_ATOMIC, q->node);
        if (!blkg)
                return NULL;

        blkg->q = q;
        INIT_LIST_HEAD(&blkg->q_node);
        INIT_LIST_HEAD(&blkg->alloc_node);
        blkg->blkcg = blkcg;
        blkg->refcnt = 1;
        cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));

        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
                struct blkio_policy_type *pol = blkio_policy[i];
                struct blkg_policy_data *pd;

                if (!pol)
                        continue;

                /* alloc per-policy data and attach it to blkg */
                pd = kzalloc_node(sizeof(*pd) + pol->pdata_size, GFP_ATOMIC,
                                  q->node);
                if (!pd) {
                        blkg_free(blkg);
                        return NULL;
                }

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

        /* invoke per-policy init */
        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
                struct blkio_policy_type *pol = blkio_policy[i];

                if (pol)
                        pol->ops.blkio_init_group_fn(blkg);
        }

        return blkg;
}

struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg,
                                       struct request_queue *q,
                                       bool for_root)
        __releases(q->queue_lock) __acquires(q->queue_lock)
{
        struct blkio_group *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.
         * The following can be removed if blkg lookup is guaranteed to
         * fail on a bypassing queue.
         */
        if (unlikely(blk_queue_bypass(q)) && !for_root)
                return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);

        blkg = blkg_lookup(blkcg, q);
        if (blkg)
                return blkg;

        /* blkg holds a reference to blkcg */
        if (!css_tryget(&blkcg->css))
                return ERR_PTR(-EINVAL);

        /*
         * Allocate and initialize.
         */
        blkg = blkg_alloc(blkcg, q);

        /* did alloc fail? */
        if (unlikely(!blkg)) {
                blkg = ERR_PTR(-ENOMEM);
                goto out;
        }

        /* insert */
        spin_lock(&blkcg->lock);
        hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
        list_add(&blkg->q_node, &q->blkg_list);
        spin_unlock(&blkcg->lock);

        spin_lock(&alloc_list_lock);
        list_add(&blkg->alloc_node, &alloc_list);
        /* Queue per cpu stat allocation from worker thread. */
        queue_delayed_work(system_nrt_wq, &blkio_stat_alloc_work, 0);
        spin_unlock(&alloc_list_lock);
out:
        return blkg;
}
EXPORT_SYMBOL_GPL(blkg_lookup_create);

/* called under rcu_read_lock(). */
struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg,
                                struct request_queue *q)
{
        struct blkio_group *blkg;
        struct hlist_node *n;

        hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node)
                if (blkg->q == q)
                        return blkg;
        return NULL;
}
EXPORT_SYMBOL_GPL(blkg_lookup);

static void blkg_destroy(struct blkio_group *blkg)
{
        struct request_queue *q = blkg->q;
        struct blkio_cgroup *blkcg = blkg->blkcg;

        lockdep_assert_held(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));
        list_del_init(&blkg->q_node);
        hlist_del_init_rcu(&blkg->blkcg_node);

        spin_lock(&alloc_list_lock);
        list_del_init(&blkg->alloc_node);
        spin_unlock(&alloc_list_lock);

        /*
         * Put the reference taken at the time of creation so that when all
         * queues are gone, group can be destroyed.
         */
        blkg_put(blkg);
}

/*
 * XXX: This updates blkg policy data in-place for root blkg, which is
 * necessary across elevator switch and policy registration as root blkgs
 * aren't shot down.  This broken and racy implementation is temporary.
 * Eventually, blkg shoot down will be replaced by proper in-place update.
 */
void update_root_blkg_pd(struct request_queue *q, enum blkio_policy_id plid)
{
        struct blkio_policy_type *pol = blkio_policy[plid];
        struct blkio_group *blkg = blkg_lookup(&blkio_root_cgroup, q);
        struct blkg_policy_data *pd;

        if (!blkg)
                return;

        kfree(blkg->pd[plid]);
        blkg->pd[plid] = NULL;

        if (!pol)
                return;

        pd = kzalloc(sizeof(*pd) + pol->pdata_size, GFP_KERNEL);
        WARN_ON_ONCE(!pd);

        pd->stats_cpu = alloc_percpu(struct blkio_group_stats_cpu);
        WARN_ON_ONCE(!pd->stats_cpu);

        blkg->pd[plid] = pd;
        pd->blkg = blkg;
        pol->ops.blkio_init_group_fn(blkg);
}
EXPORT_SYMBOL_GPL(update_root_blkg_pd);

/**
 * blkg_destroy_all - destroy all blkgs associated with a request_queue
 * @q: request_queue of interest
 * @destroy_root: whether to destroy root blkg or not
 *
 * Destroy blkgs associated with @q.  If @destroy_root is %true, all are
 * destroyed; otherwise, root blkg is left alone.
 */
void blkg_destroy_all(struct request_queue *q, bool destroy_root)
{
        struct blkio_group *blkg, *n;

        spin_lock_irq(q->queue_lock);

        list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
                struct blkio_cgroup *blkcg = blkg->blkcg;

                /* skip root? */
                if (!destroy_root && blkg->blkcg == &blkio_root_cgroup)
                        continue;

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

        spin_unlock_irq(q->queue_lock);
}
EXPORT_SYMBOL_GPL(blkg_destroy_all);

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

void __blkg_release(struct blkio_group *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);

static void blkio_reset_stats_cpu(struct blkio_group *blkg, int plid)
{
        struct blkg_policy_data *pd = blkg->pd[plid];
        int cpu;

        if (pd->stats_cpu == NULL)
                return;

        for_each_possible_cpu(cpu) {
                struct blkio_group_stats_cpu *sc =
                        per_cpu_ptr(pd->stats_cpu, cpu);

                blkg_rwstat_reset(&sc->service_bytes);
                blkg_rwstat_reset(&sc->serviced);
                blkg_stat_reset(&sc->sectors);
        }
}

static int
blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
        struct blkio_group *blkg;
        struct hlist_node *n;

        spin_lock(&blkio_list_lock);
        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) {
                struct blkio_policy_type *pol;

                list_for_each_entry(pol, &blkio_list, list) {
                        struct blkg_policy_data *pd = blkg->pd[pol->plid];
                        struct blkio_group_stats *stats = &pd->stats;

                        /* queued stats shouldn't be cleared */
                        blkg_rwstat_reset(&stats->merged);
                        blkg_rwstat_reset(&stats->service_time);
                        blkg_rwstat_reset(&stats->wait_time);
                        blkg_stat_reset(&stats->time);
#ifdef CONFIG_DEBUG_BLK_CGROUP
                        blkg_stat_reset(&stats->unaccounted_time);
                        blkg_stat_reset(&stats->avg_queue_size_sum);
                        blkg_stat_reset(&stats->avg_queue_size_samples);
                        blkg_stat_reset(&stats->dequeue);
                        blkg_stat_reset(&stats->group_wait_time);
                        blkg_stat_reset(&stats->idle_time);
                        blkg_stat_reset(&stats->empty_time);
#endif
                        blkio_reset_stats_cpu(blkg, pol->plid);
                }
        }

        spin_unlock_irq(&blkcg->lock);
        spin_unlock(&blkio_list_lock);
        return 0;
}

static const char *blkg_dev_name(struct blkio_group *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.
 */
static void blkcg_print_blkgs(struct seq_file *sf, struct blkio_cgroup *blkcg,
                              u64 (*prfill)(struct seq_file *,
                                            struct blkg_policy_data *, int),
                              int pol, int data, bool show_total)
{
        struct blkio_group *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 (blkg->pd[pol])
                        total += prfill(sf, blkg->pd[pol], data);
        spin_unlock_irq(&blkcg->lock);

        if (show_total)
                seq_printf(sf, "Total %llu\n", (unsigned long long)total);
}

/**
 * __blkg_prfill_u64 - prfill helper for a single u64 value
 * @sf: seq_file to print to
 * @pd: policy data of interest
 * @v: value to print
 *
 * Print @v to @sf for the device assocaited with @pd.
 */
static 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;
}

/**
 * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
 * @sf: seq_file to print to
 * @pd: policy data of interest
 * @rwstat: rwstat to print
 *
 * Print @rwstat to @sf for the device assocaited with @pd.
 */
static 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;
}

static 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->stats + off));
}

static u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
                              int off)
{
        struct blkg_rwstat rwstat = blkg_rwstat_read((void *)&pd->stats + off);

        return __blkg_prfill_rwstat(sf, pd, &rwstat);
}

/* print blkg_stat specified by BLKCG_STAT_PRIV() */
static int blkcg_print_stat(struct cgroup *cgrp, struct cftype *cft,
                            struct seq_file *sf)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);

        blkcg_print_blkgs(sf, blkcg, blkg_prfill_stat,
                          BLKCG_STAT_POL(cft->private),
                          BLKCG_STAT_OFF(cft->private), false);
        return 0;
}

/* print blkg_rwstat specified by BLKCG_STAT_PRIV() */
static int blkcg_print_rwstat(struct cgroup *cgrp, struct cftype *cft,
                              struct seq_file *sf)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);

        blkcg_print_blkgs(sf, blkcg, blkg_prfill_rwstat,
                          BLKCG_STAT_POL(cft->private),
                          BLKCG_STAT_OFF(cft->private), true);
        return 0;
}

static u64 blkg_prfill_cpu_stat(struct seq_file *sf,
                                struct blkg_policy_data *pd, int off)
{
        u64 v = 0;
        int cpu;

        for_each_possible_cpu(cpu) {
                struct blkio_group_stats_cpu *sc =
                        per_cpu_ptr(pd->stats_cpu, cpu);

                v += blkg_stat_read((void *)sc + off);
        }

        return __blkg_prfill_u64(sf, pd, v);
}

static u64 blkg_prfill_cpu_rwstat(struct seq_file *sf,
                                  struct blkg_policy_data *pd, int off)
{
        struct blkg_rwstat rwstat = { }, tmp;
        int i, cpu;

        for_each_possible_cpu(cpu) {
                struct blkio_group_stats_cpu *sc =
                        per_cpu_ptr(pd->stats_cpu, cpu);

                tmp = blkg_rwstat_read((void *)sc + off);
                for (i = 0; i < BLKG_RWSTAT_NR; i++)
                        rwstat.cnt[i] += tmp.cnt[i];
        }

        return __blkg_prfill_rwstat(sf, pd, &rwstat);
}

/* print per-cpu blkg_stat specified by BLKCG_STAT_PRIV() */
static int blkcg_print_cpu_stat(struct cgroup *cgrp, struct cftype *cft,
                                struct seq_file *sf)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);

        blkcg_print_blkgs(sf, blkcg, blkg_prfill_cpu_stat,
                          BLKCG_STAT_POL(cft->private),
                          BLKCG_STAT_OFF(cft->private), false);
        return 0;
}

/* print per-cpu blkg_rwstat specified by BLKCG_STAT_PRIV() */
static int blkcg_print_cpu_rwstat(struct cgroup *cgrp, struct cftype *cft,
                                  struct seq_file *sf)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);

        blkcg_print_blkgs(sf, blkcg, blkg_prfill_cpu_rwstat,
                          BLKCG_STAT_POL(cft->private),
                          BLKCG_STAT_OFF(cft->private), true);
        return 0;
}

#ifdef CONFIG_DEBUG_BLK_CGROUP
static u64 blkg_prfill_avg_queue_size(struct seq_file *sf,
                                      struct blkg_policy_data *pd, int off)
{
        u64 samples = blkg_stat_read(&pd->stats.avg_queue_size_samples);
        u64 v = 0;

        if (samples) {
                v = blkg_stat_read(&pd->stats.avg_queue_size_sum);
                do_div(v, samples);
        }
        __blkg_prfill_u64(sf, pd, v);
        return 0;
}

/* print avg_queue_size */
static int blkcg_print_avg_queue_size(struct cgroup *cgrp, struct cftype *cft,
                                      struct seq_file *sf)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);

        blkcg_print_blkgs(sf, blkcg, blkg_prfill_avg_queue_size,
                          BLKIO_POLICY_PROP, 0, false);
        return 0;
}
#endif  /* CONFIG_DEBUG_BLK_CGROUP */

static int blkio_policy_parse_and_set(char *buf, enum blkio_policy_id plid,
                                      int fileid, struct blkio_cgroup *blkcg)
{
        struct gendisk *disk = NULL;
        struct blkio_group *blkg = NULL;
        struct blkg_policy_data *pd;
        char *s[4], *p, *major_s = NULL, *minor_s = NULL;
        unsigned long major, minor;
        int i = 0, ret = -EINVAL;
        int part;
        dev_t dev;
        u64 temp;

        memset(s, 0, sizeof(s));

        while ((p = strsep(&buf, " ")) != NULL) {
                if (!*p)
                        continue;

                s[i++] = p;

                /* Prevent from inputing too many things */
                if (i == 3)
                        break;
        }

        if (i != 2)
                goto out;

        p = strsep(&s[0], ":");
        if (p != NULL)
                major_s = p;
        else
                goto out;

        minor_s = s[0];
        if (!minor_s)
                goto out;

        if (strict_strtoul(major_s, 10, &major))
                goto out;

        if (strict_strtoul(minor_s, 10, &minor))
                goto out;

        dev = MKDEV(major, minor);

        if (strict_strtoull(s[1], 10, &temp))
                goto out;

        disk = get_gendisk(dev, &part);
        if (!disk || part)
                goto out;

        rcu_read_lock();

        spin_lock_irq(disk->queue->queue_lock);
        blkg = blkg_lookup_create(blkcg, disk->queue, false);
        spin_unlock_irq(disk->queue->queue_lock);

        if (IS_ERR(blkg)) {
                ret = PTR_ERR(blkg);
                goto out_unlock;
        }

        pd = blkg->pd[plid];

        switch (plid) {
        case BLKIO_POLICY_PROP:
                if ((temp < BLKIO_WEIGHT_MIN && temp > 0) ||
                     temp > BLKIO_WEIGHT_MAX)
                        goto out_unlock;

                pd->conf.weight = temp;
                blkio_update_group_weight(blkg, plid, temp ?: blkcg->weight);
                break;
        case BLKIO_POLICY_THROTL:
                switch(fileid) {
                case BLKIO_THROTL_read_bps_device:
                        pd->conf.bps[READ] = temp;
                        blkio_update_group_bps(blkg, plid, temp ?: -1, fileid);
                        break;
                case BLKIO_THROTL_write_bps_device:
                        pd->conf.bps[WRITE] = temp;
                        blkio_update_group_bps(blkg, plid, temp ?: -1, fileid);
                        break;
                case BLKIO_THROTL_read_iops_device:
                        if (temp > THROTL_IOPS_MAX)
                                goto out_unlock;
                        pd->conf.iops[READ] = temp;
                        blkio_update_group_iops(blkg, plid, temp ?: -1, fileid);
                        break;
                case BLKIO_THROTL_write_iops_device:
                        if (temp > THROTL_IOPS_MAX)
                                goto out_unlock;
                        pd->conf.iops[WRITE] = temp;
                        blkio_update_group_iops(blkg, plid, temp ?: -1, fileid);
                        break;
                }
                break;
        default:
                BUG();
        }
        ret = 0;
out_unlock:
        rcu_read_unlock();
out:
        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);
                return restart_syscall();
        }
        return ret;
}

static int blkiocg_file_write(struct cgroup *cgrp, struct cftype *cft,
                                       const char *buffer)
{
        int ret = 0;
        char *buf;
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);
        enum blkio_policy_id plid = BLKIOFILE_POLICY(cft->private);
        int fileid = BLKIOFILE_ATTR(cft->private);

        buf = kstrdup(buffer, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        ret = blkio_policy_parse_and_set(buf, plid, fileid, blkcg);
        kfree(buf);
        return ret;
}

static void blkio_print_group_conf(struct cftype *cft, struct blkio_group *blkg,
                                   struct seq_file *m)
{
        int plid = BLKIOFILE_POLICY(cft->private);
        int fileid = BLKIOFILE_ATTR(cft->private);
        struct blkg_policy_data *pd = blkg->pd[plid];
        const char *dname = blkg_dev_name(blkg);
        int rw = WRITE;

        if (!dname)
                return;

        switch (plid) {
                case BLKIO_POLICY_PROP:
                        if (pd->conf.weight)
                                seq_printf(m, "%s\t%u\n",
                                           dname, pd->conf.weight);
                        break;
                case BLKIO_POLICY_THROTL:
                        switch (fileid) {
                        case BLKIO_THROTL_read_bps_device:
                                rw = READ;
                        case BLKIO_THROTL_write_bps_device:
                                if (pd->conf.bps[rw])
                                        seq_printf(m, "%s\t%llu\n",
                                                   dname, pd->conf.bps[rw]);
                                break;
                        case BLKIO_THROTL_read_iops_device:
                                rw = READ;
                        case BLKIO_THROTL_write_iops_device:
                                if (pd->conf.iops[rw])
                                        seq_printf(m, "%s\t%u\n",
                                                   dname, pd->conf.iops[rw]);
                                break;
                        }
                        break;
                default:
                        BUG();
        }
}

/* cgroup files which read their data from policy nodes end up here */
static void blkio_read_conf(struct cftype *cft, struct blkio_cgroup *blkcg,
                            struct seq_file *m)
{
        struct blkio_group *blkg;
        struct hlist_node *n;

        spin_lock_irq(&blkcg->lock);
        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
                blkio_print_group_conf(cft, blkg, m);
        spin_unlock_irq(&blkcg->lock);
}

static int blkiocg_file_read(struct cgroup *cgrp, struct cftype *cft,
                                struct seq_file *m)
{
        struct blkio_cgroup *blkcg;
        enum blkio_policy_id plid = BLKIOFILE_POLICY(cft->private);
        int name = BLKIOFILE_ATTR(cft->private);

        blkcg = cgroup_to_blkio_cgroup(cgrp);

        switch(plid) {
        case BLKIO_POLICY_PROP:
                switch(name) {
                case BLKIO_PROP_weight_device:
                        blkio_read_conf(cft, blkcg, m);
                        return 0;
                default:
                        BUG();
                }
                break;
        case BLKIO_POLICY_THROTL:
                switch(name){
                case BLKIO_THROTL_read_bps_device:
                case BLKIO_THROTL_write_bps_device:
                case BLKIO_THROTL_read_iops_device:
                case BLKIO_THROTL_write_iops_device:
                        blkio_read_conf(cft, blkcg, m);
                        return 0;
                default:
                        BUG();
                }
                break;
        default:
                BUG();
        }

        return 0;
}

static int blkio_weight_write(struct blkio_cgroup *blkcg, int plid, u64 val)
{
        struct blkio_group *blkg;
        struct hlist_node *n;

        if (val < BLKIO_WEIGHT_MIN || val > BLKIO_WEIGHT_MAX)
                return -EINVAL;

        spin_lock(&blkio_list_lock);
        spin_lock_irq(&blkcg->lock);
        blkcg->weight = (unsigned int)val;

        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
                struct blkg_policy_data *pd = blkg->pd[plid];

                if (!pd->conf.weight)
                        blkio_update_group_weight(blkg, plid, blkcg->weight);
        }

        spin_unlock_irq(&blkcg->lock);
        spin_unlock(&blkio_list_lock);
        return 0;
}

static u64 blkiocg_file_read_u64 (struct cgroup *cgrp, struct cftype *cft) {
        struct blkio_cgroup *blkcg;
        enum blkio_policy_id plid = BLKIOFILE_POLICY(cft->private);
        int name = BLKIOFILE_ATTR(cft->private);

        blkcg = cgroup_to_blkio_cgroup(cgrp);

        switch(plid) {
        case BLKIO_POLICY_PROP:
                switch(name) {
                case BLKIO_PROP_weight:
                        return (u64)blkcg->weight;
                }
                break;
        default:
                BUG();
        }
        return 0;
}

static int
blkiocg_file_write_u64(struct cgroup *cgrp, struct cftype *cft, u64 val)
{
        struct blkio_cgroup *blkcg;
        enum blkio_policy_id plid = BLKIOFILE_POLICY(cft->private);
        int name = BLKIOFILE_ATTR(cft->private);

        blkcg = cgroup_to_blkio_cgroup(cgrp);

        switch(plid) {
        case BLKIO_POLICY_PROP:
                switch(name) {
                case BLKIO_PROP_weight:
                        return blkio_weight_write(blkcg, plid, val);
                }
                break;
        default:
                BUG();
        }

        return 0;
}

struct cftype blkio_files[] = {
        {
                .name = "weight_device",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_PROP,
                                BLKIO_PROP_weight_device),
                .read_seq_string = blkiocg_file_read,
                .write_string = blkiocg_file_write,
                .max_write_len = 256,
        },
        {
                .name = "weight",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_PROP,
                                BLKIO_PROP_weight),
                .read_u64 = blkiocg_file_read_u64,
                .write_u64 = blkiocg_file_write_u64,
        },
        {
                .name = "time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, time)),
                .read_seq_string = blkcg_print_stat,
        },
        {
                .name = "sectors",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats_cpu, sectors)),
                .read_seq_string = blkcg_print_cpu_stat,
        },
        {
                .name = "io_service_bytes",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats_cpu, service_bytes)),
                .read_seq_string = blkcg_print_cpu_rwstat,
        },
        {
                .name = "io_serviced",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats_cpu, serviced)),
                .read_seq_string = blkcg_print_cpu_rwstat,
        },
        {
                .name = "io_service_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, service_time)),
                .read_seq_string = blkcg_print_rwstat,
        },
        {
                .name = "io_wait_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, wait_time)),
                .read_seq_string = blkcg_print_rwstat,
        },
        {
                .name = "io_merged",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, merged)),
                .read_seq_string = blkcg_print_rwstat,
        },
        {
                .name = "io_queued",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, queued)),
                .read_seq_string = blkcg_print_rwstat,
        },
        {
                .name = "reset_stats",
                .write_u64 = blkiocg_reset_stats,
        },
#ifdef CONFIG_BLK_DEV_THROTTLING
        {
                .name = "throttle.read_bps_device",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_THROTL,
                                BLKIO_THROTL_read_bps_device),
                .read_seq_string = blkiocg_file_read,
                .write_string = blkiocg_file_write,
                .max_write_len = 256,
        },

        {
                .name = "throttle.write_bps_device",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_THROTL,
                                BLKIO_THROTL_write_bps_device),
                .read_seq_string = blkiocg_file_read,
                .write_string = blkiocg_file_write,
                .max_write_len = 256,
        },

        {
                .name = "throttle.read_iops_device",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_THROTL,
                                BLKIO_THROTL_read_iops_device),
                .read_seq_string = blkiocg_file_read,
                .write_string = blkiocg_file_write,
                .max_write_len = 256,
        },

        {
                .name = "throttle.write_iops_device",
                .private = BLKIOFILE_PRIVATE(BLKIO_POLICY_THROTL,
                                BLKIO_THROTL_write_iops_device),
                .read_seq_string = blkiocg_file_read,
                .write_string = blkiocg_file_write,
                .max_write_len = 256,
        },
        {
                .name = "throttle.io_service_bytes",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_THROTL,
                                offsetof(struct blkio_group_stats_cpu, service_bytes)),
                .read_seq_string = blkcg_print_cpu_rwstat,
        },
        {
                .name = "throttle.io_serviced",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_THROTL,
                                offsetof(struct blkio_group_stats_cpu, serviced)),
                .read_seq_string = blkcg_print_cpu_rwstat,
        },
#endif /* CONFIG_BLK_DEV_THROTTLING */

#ifdef CONFIG_DEBUG_BLK_CGROUP
        {
                .name = "avg_queue_size",
                .read_seq_string = blkcg_print_avg_queue_size,
        },
        {
                .name = "group_wait_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, group_wait_time)),
                .read_seq_string = blkcg_print_stat,
        },
        {
                .name = "idle_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, idle_time)),
                .read_seq_string = blkcg_print_stat,
        },
        {
                .name = "empty_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, empty_time)),
                .read_seq_string = blkcg_print_stat,
        },
        {
                .name = "dequeue",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, dequeue)),
                .read_seq_string = blkcg_print_stat,
        },
        {
                .name = "unaccounted_time",
                .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
                                offsetof(struct blkio_group_stats, unaccounted_time)),
                .read_seq_string = blkcg_print_stat,
        },
#endif
        { }     /* terminate */
};

/**
 * blkiocg_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 blkiocg_pre_destroy(struct cgroup *cgroup)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);

        spin_lock_irq(&blkcg->lock);

        while (!hlist_empty(&blkcg->blkg_list)) {
                struct blkio_group *blkg = hlist_entry(blkcg->blkg_list.first,
                                                struct blkio_group, 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 blkiocg_destroy(struct cgroup *cgroup)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);

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

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

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

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

        blkcg->weight = BLKIO_WEIGHT_DEFAULT;
        blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
done:
        spin_lock_init(&blkcg->lock);
        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)
{
        int ret;

        might_sleep();

        ret = blk_throtl_init(q);
        if (ret)
                return ret;

        mutex_lock(&all_q_mutex);
        INIT_LIST_HEAD(&q->all_q_node);
        list_add_tail(&q->all_q_node, &all_q_list);
        mutex_unlock(&all_q_mutex);

        return 0;
}

/**
 * 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)
{
        mutex_lock(&all_q_mutex);
        list_del_init(&q->all_q_node);
        mutex_unlock(&all_q_mutex);

        blkg_destroy_all(q, true);

        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 blkiocg_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;
}

static void blkcg_bypass_start(void)
        __acquires(&all_q_mutex)
{
        struct request_queue *q;

        mutex_lock(&all_q_mutex);

        list_for_each_entry(q, &all_q_list, all_q_node) {
                blk_queue_bypass_start(q);
                blkg_destroy_all(q, false);
        }
}

static void blkcg_bypass_end(void)
        __releases(&all_q_mutex)
{
        struct request_queue *q;

        list_for_each_entry(q, &all_q_list, all_q_node)
                blk_queue_bypass_end(q);

        mutex_unlock(&all_q_mutex);
}

struct cgroup_subsys blkio_subsys = {
        .name = "blkio",
        .create = blkiocg_create,
        .can_attach = blkiocg_can_attach,
        .pre_destroy = blkiocg_pre_destroy,
        .destroy = blkiocg_destroy,
        .subsys_id = blkio_subsys_id,
        .base_cftypes = blkio_files,
        .module = THIS_MODULE,
};
EXPORT_SYMBOL_GPL(blkio_subsys);

void blkio_policy_register(struct blkio_policy_type *blkiop)
{
        struct request_queue *q;

        blkcg_bypass_start();
        spin_lock(&blkio_list_lock);

        BUG_ON(blkio_policy[blkiop->plid]);
        blkio_policy[blkiop->plid] = blkiop;
        list_add_tail(&blkiop->list, &blkio_list);

        spin_unlock(&blkio_list_lock);
        list_for_each_entry(q, &all_q_list, all_q_node)
                update_root_blkg_pd(q, blkiop->plid);
        blkcg_bypass_end();
}
EXPORT_SYMBOL_GPL(blkio_policy_register);

void blkio_policy_unregister(struct blkio_policy_type *blkiop)
{
        struct request_queue *q;

        blkcg_bypass_start();
        spin_lock(&blkio_list_lock);

        BUG_ON(blkio_policy[blkiop->plid] != blkiop);
        blkio_policy[blkiop->plid] = NULL;
        list_del_init(&blkiop->list);

        spin_unlock(&blkio_list_lock);
        list_for_each_entry(q, &all_q_list, all_q_node)
                update_root_blkg_pd(q, blkiop->plid);
        blkcg_bypass_end();
}
EXPORT_SYMBOL_GPL(blkio_policy_unregister);