freezer_cg: fix improper BUG_ON() causing oops

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>
Acked-by: Cedric Le Goater <clg@fr.ibm.com>
Acked-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e950569..7f54d1c 100644 (file)
--- 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);