[PATCH 1/4] freezer_cg: fix improper BUG_ON() causing oops

[Li Zefan <lizf@cn.fujitsu.com>]

The BUG_ON() should be protected by freezer->lock, otherwise it
can be triggered easily when a task has been unfreezed but the
corresponding cgroup hasn't been changed to FROZEN state.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cgroup_freezer.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e950569..7f54d1c 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -190,8 +190,9 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 	freezer = task_freezer(task);
 	task_unlock(task);
 
-	BUG_ON(freezer->state == CGROUP_FROZEN);
 	spin_lock_irq(&freezer->lock);
+	BUG_ON(freezer->state == CGROUP_FROZEN);
+
 	/* Locking avoids race with FREEZING -> THAWED transitions. */
 	if (freezer->state == CGROUP_FREEZING)
 		freeze_task(task, true);
-- 
1.5.4.rc3