On Fri, Dec 23, 2011 at 04:25:23AM +0100, Frederic Weisbecker wrote:

cgroup_post_fork() is protected between threadgroup_change_begin()
and threadgroup_change_end() against concurrent changes of the
child's css_set in cgroup_task_migrate(). Also the child can't
exit and call cgroup_exit() at this stage, this means it's css_set
can't be changed with init_css_set concurrently.

For these reasons, we don't need to hold task_lock() on the child
because it's css_set can only remain stable in this place.

Let's remove the lock there.

v2: Update comment to explain that we are safe against
cgroup_exit()

Signed-off-by: Frederic Weisbecker <redacted>
Cc: Li Zefan <redacted>
Cc: Tejun Heo <redacted>
Cc: Containers <redacted>
Cc: Cgroups <redacted>
Cc: KAMEZAWA Hiroyuki <redacted>
Cc: Oleg Nesterov <redacted>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: Paul Menage <redacted>
Cc: Mandeep Singh Baines <redacted>

Li, does this look good to you?

Thanks.

-- 
tejun