Revert "cgroup: Drop task_lock(parent) on cgroup_fork()"
authorTejun Heo <tj@kernel.org>
Fri, 19 Oct 2012 00:52:07 +0000 (17:52 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sun, 28 Oct 2012 17:56:14 +0000 (10:56 -0700)
commit04900efcfcd89fd11302748bbe88659d12fd7fb5
treedfc42bf26f79c54d8bd9c9b86b0cd98fff8f664f
parentb4cd7aa6602e17f7c128ddf0c9b0dc7b4e2b897c
Revert "cgroup: Drop task_lock(parent) on cgroup_fork()"

commit 9bb71308b8133d643648776243e4d5599b1c193d upstream.

This reverts commit 7e381b0eb1e1a9805c37335562e8dc02e7d7848c.

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>
Bitterly-Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/cgroup.c