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From: Li Zefan on 22 Apr 2010 22:40
task_subsys_state() is safe under task_lock(). See
Documentation/cgroups/cgroups.txt for locking rule.

This fixes an RCU warning when resume from suspend. The
warning comes from freezer cgroup in cgroup_freezing_or_frozen().

Signed-off-by: Li Zefan <lizf(a)cn.fujitsu.com>
---

I'm not sure which is preferable - access ->alloc_lock directly
like this patch or add task_lock_is_held() in sched.h

---
include/linux/cgroup.h | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b8ad1ea..8f78073 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -530,6 +530,7 @@ static inline struct cgroup_subsys_state *task_subsys_state(
{
return rcu_dereference_check(task->cgroups->subsys[subsys_id],
rcu_read_lock_held() ||
+ lockdep_is_held(&task->alloc_lock) ||
cgroup_lock_is_held());
}

--
1.6.3
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