Revert "cgroup: Remove task_lock() from cgroup_post_fork()"
commit
d87838321124061f6c935069d97f37010fa417e6 upstream.
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
locks.
Revert the incorrect optimization.
Signed-off-by: Tejun Heo <tj@kernel.org>
LKML-Reference: <
20121008020000.GB2575@localhost>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>