FreeBSD/Linux Kernel Cross Reference
sys/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/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_dying(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);
           }
   
           /*
            * root blkg is destroyed.  Just clear the pointer since
            * root_rl does not take reference on root blkg.
            */
           q->root_blkg = NULL;
           q->root_rl.blkg = NULL;
   }
   
   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;
                   /* There are no more block groups, hence no request lists */
                   if (list_empty(ent))
                           return NULL;
           } else {
                   blkg = container_of(rl, struct blkcg_gq, rl);
                   ent = &blkg->q_node;
           }
   
           /* walk to the next list_head, skip root blkcg */
           ent = ent->next;
           if (ent == &q->root_blkg->q_node)
                   ent = ent->next;
           if (ent == &q->blkg_list)
                   return NULL;
   
           blkg = container_of(ent, struct blkcg_gq, q_node);
           return &blkg->rl;
   }
   
   static int blkcg_reset_stats(struct cgroup *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_css_offline - cgroup css_offline 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 void blkcg_css_offline(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);
   }
   
   static void blkcg_css_free(struct cgroup *cgroup)
   {
           struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
   
           if (blkcg != &blkcg_root)
                   kfree(blkcg);
   }
   
   static struct cgroup_subsys_state *blkcg_css_alloc(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",
           .css_alloc = blkcg_css_alloc,
           .css_offline = blkcg_css_offline,
           .css_free = blkcg_css_free,
           .can_attach = blkcg_can_attach,
           .subsys_id = blkio_subsys_id,
           .base_cftypes = blkcg_files,
           .module = THIS_MODULE,
   
           /*
            * blkio subsystem is utterly broken in terms of hierarchy support.
            * It treats all cgroups equally regardless of where they're
            * located in the hierarchy - all cgroups are treated as if they're
            * right below the root.  Fix it and remove the following.
            */
           .broken_hierarchy = true,
   };
   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);

Cache object: 84e0f449909f39f00ae72f8d40acc09c