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From: Paul E. McKenney on 21 Apr 2010 16:10
Add an RCU read-side critical section to suppress this false positive.

Located-by: Eric Paris <eparis(a)parisplace.org>
Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com>
Acked-by: Li Zefan <lizf(a)cn.fujitsu.com>
---
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
--
1.7.0

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