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From: Paul E. McKenney on 3 May 2010 15:00
From: Li Zefan <lizf(a)cn.fujitsu.com>

Expand task_subsys_state()'s rcu_dereference_check() to include the full
locking rule as documented in Documentation/cgroups/cgroups.txt by adding
a check for task->alloc_lock being held.

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

Signed-off-by: Li Zefan <lizf(a)cn.fujitsu.com>
Acked-by: Matt Helsley <matthltc(a)us.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com>
---
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());
}

--
1.7.0

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Prev: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
Next: [PATCH tip/core/urgent 09/10] blk-cgroup: Fix RCU correctness warning in cfq_init_queue()