Revert "cgroup: Remove task_lock() from cgroup_post_fork()"
authorTejun Heo <tj@kernel.org>
Fri, 19 Oct 2012 00:40:30 +0000 (17:40 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sun, 28 Oct 2012 17:56:14 +0000 (10:56 -0700)
commitb4cd7aa6602e17f7c128ddf0c9b0dc7b4e2b897c
tree44ab2e59ccc7d5eb101cced1de21295cde4751ce
parent52f65d5b473c7d5bc166ed7f86570be7852edb9a
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>
kernel/cgroup.c