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 <[email protected]>
Acked-by: Cedric Le Goater <[email protected]>
Acked-by: Matt Helsley <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e95056954498e42e2f225216eaa0cd6286b6f7b6..7f54d1c42953601fe4a54a4c174e21238b8f7ce4 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);