[PATCH 5/5] blk-cgroup: Fix an RCU warning in blkiocg_create()

Li Zefan
2010-04-22T09:30:42Z

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: Li Zefan <lizf@cn.fujitsu.com>
---
block/blk-cgroup.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 5fe03de..2cc682b 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -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);
--
1.6.3