Commit 0341509f authored by Li Zefan's avatar Li Zefan Committed by Jens Axboe

blk-cgroup: Fix an RCU warning in blkiocg_create()

with CONFIG_PROVE_RCU=y, a warning can be triggered:

  # mount -t cgroup -o blkio xxx /mnt
  # mkdir /mnt/subgroup

kernel/cgroup.c:4442 invoked rcu_dereference_check() without protection!

To fix this, we avoid caling css_depth() here, which is a bit simpler
than the original code.
Signed-off-by: default avatarLi Zefan <>
Acked-by: default avatarVivek Goyal <>
Signed-off-by: default avatarJens Axboe <>
parent dcf097b2
......@@ -286,16 +286,16 @@ done:
static struct cgroup_subsys_state *
blkiocg_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
struct blkio_cgroup *blkcg, *parent_blkcg;
struct blkio_cgroup *blkcg;
struct cgroup *parent = cgroup->parent;
if (!cgroup->parent) {
if (!parent) {
blkcg = &blkio_root_cgroup;
goto done;
/* Currently we do not support hierarchy deeper than two level (0,1) */
parent_blkcg = cgroup_to_blkio_cgroup(cgroup->parent);
if (css_depth(&parent_blkcg->css) > 0)
if (parent != cgroup->top_cgroup)
return ERR_PTR(-EINVAL);
blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
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