Revert "cgroup: Remove task_lock() from cgroup_post_fork()"

This reverts commit 7e3aa30ac8c904a706518b725c451bb486daaae9.

The commit incorrectly assumed that fork path always performed
threadgroup_change_begin/end() and depended on that for
synchronization against task exit and cgroup migration paths instead
of explicitly grabbing task_lock().

threadgroup_change is not locked when forking a new process (as
opposed to a new thread in the same process) and even if it were it
wouldn't be effective as different processes use different threadgroup

Revert the incorrect optimization.

Signed-off-by: Tejun Heo <>
LKML-Reference: <20121008020000.GB2575@localhost>
Acked-by: Li Zefan <>
Cc: Frederic Weisbecker <>
1 file changed