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Subject[PATCH tip/core/urgent 05/10] cgroup: Fix an RCU warning in alloc_css_id()
Date
From: Li Zefan <lizf@cn.fujitsu.com>

With CONFIG_PROVE_RCU=y, a warning can be triggered:

# mount -t cgroup -o memory xxx /mnt
# mkdir /mnt/0

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

This is a false-positive. It's safe to directly access parent_css->id.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/cgroup.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4ca928d..3a53c77 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4561,13 +4561,13 @@ static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
{
int subsys_id, i, depth = 0;
struct cgroup_subsys_state *parent_css, *child_css;
- struct css_id *child_id, *parent_id = NULL;
+ struct css_id *child_id, *parent_id;

subsys_id = ss->subsys_id;
parent_css = parent->subsys[subsys_id];
child_css = child->subsys[subsys_id];
- depth = css_depth(parent_css) + 1;
parent_id = parent_css->id;
+ depth = parent_id->depth;

child_id = get_new_cssid(ss, depth);
if (IS_ERR(child_id))
--
1.7.0


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