From: tip-bot for Paul E. McKenney on
Commit-ID: 8b46f880841aac821af8efa6581bb0e46b8b9845
Author: Paul E. McKenney <paulmck(a)>
AuthorDate: Wed, 21 Apr 2010 13:02:08 -0700
Committer: Ingo Molnar <mingo(a)>
CommitDate: Fri, 30 Apr 2010 12:03:17 +0200

rcu: Fix RCU lockdep splat on freezer_fork path

Add an RCU read-side critical section to suppress this false

Located-by: Eric Paris <eparis(a)>
Signed-off-by: Paul E. McKenney <paulmck(a)>
Acked-by: Li Zefan <lizf(a)>
Cc: laijs(a)
Cc: dipankar(a)
Cc: mathieu.desnoyers(a)
Cc: josh(a)
Cc: dvhltc(a)
Cc: niv(a)
Cc: peterz(a)
Cc: rostedt(a)
Cc: Valdis.Kletnieks(a)
Cc: dhowells(a)
Cc: eric.dumazet(a)
LKML-Reference: <1271880131-3951-2-git-send-email-paulmck(a)>
Signed-off-by: Ingo Molnar <mingo(a)>
kernel/cgroup_freezer.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index da5e139..e5c0244 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
* No lock is needed, since the task isn't on tasklist yet,
* so it can't be moved to another cgroup, which means the
* freezer won't be removed and will be valid during this
- * function call.
+ * function call. Nevertheless, apply RCU read-side critical
+ * section to suppress RCU lockdep false positives.
+ rcu_read_lock();
freezer = task_freezer(task);
+ rcu_read_unlock();

* The root cgroup is non-freezable, so we can skip the
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