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blk-cgroup: defer blkcg css_put until blkg is unlinked from queue #975

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blk-cgroup: defer blkcg css_put until blkg is unlinked from queue #975

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24 changes: 12 additions & 12 deletions block/blk-cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,11 @@ static void blkg_free_workfn(struct work_struct *work)
spin_unlock_irq(&q->queue_lock);
mutex_unlock(&q->blkcg_mutex);

/*
* Release blkcg css ref only after blkg is removed from q->blkg_list,
* so concurrent iterators won't see a blkg with a freed blkcg.
*/
css_put(&blkg->blkcg->css);
blk_put_queue(q);
free_percpu(blkg->iostat_cpu);
percpu_ref_exit(&blkg->refcnt);
Expand Down Expand Up @@ -179,8 +184,6 @@ static void __blkg_release(struct rcu_head *rcu)
for_each_possible_cpu(cpu)
__blkcg_rstat_flush(blkcg, cpu);

/* release the blkcg and parent blkg refs this blkg has been holding */
css_put(&blkg->blkcg->css);
blkg_free(blkg);
}

Expand Down Expand Up @@ -313,6 +316,9 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
goto out_exit_refcnt;
if (!blk_get_queue(disk->queue))
goto out_free_iostat;
/* blkg holds a reference to blkcg */
if (!css_tryget_online(&blkcg->css))
goto out_put_queue;

blkg->q = disk->queue;
INIT_LIST_HEAD(&blkg->q_node);
Expand Down Expand Up @@ -353,6 +359,8 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
while (--i >= 0)
if (blkg->pd[i])
blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
css_put(&blkcg->css);
out_put_queue:
blk_put_queue(disk->queue);
out_free_iostat:
free_percpu(blkg->iostat_cpu);
Expand Down Expand Up @@ -381,18 +389,12 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
goto err_free_blkg;
}

/* blkg holds a reference to blkcg */
if (!css_tryget_online(&blkcg->css)) {
ret = -ENODEV;
goto err_free_blkg;
}

/* allocate */
if (!new_blkg) {
new_blkg = blkg_alloc(blkcg, disk, GFP_NOWAIT);
if (unlikely(!new_blkg)) {
ret = -ENOMEM;
goto err_put_css;
goto err_free_blkg;
}
}
blkg = new_blkg;
Expand All @@ -402,7 +404,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
blkg->parent = blkg_lookup(blkcg_parent(blkcg), disk->queue);
if (WARN_ON_ONCE(!blkg->parent)) {
ret = -ENODEV;
goto err_put_css;
goto err_free_blkg;
}
blkg_get(blkg->parent);
}
Expand Down Expand Up @@ -442,8 +444,6 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
blkg_put(blkg);
return ERR_PTR(ret);

err_put_css:
css_put(&blkcg->css);
err_free_blkg:
if (new_blkg)
blkg_free(new_blkg);
Expand Down
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