From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Is not locking task_lock in cgroup_fork() safe?
Date: Mon, 8 Oct 2012 11:00:00 +0900
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To: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

Hello, Frederic.

7e381b0eb1 ("cgroup: Drop task_lock(parent) on cgroup_fork()") removed
task_lock from cgroup_fork citing that current->cgroups can't change
due to threadgroup_change locking; however, threadgroup_change locking
is used only during CLONE_THREAD forking.  If @current is forking a
new process, there's nothing preventing someone else to migrate the
parent while forking is in progress and delete the css_set it
currently is using.  Am I confused somewhere?

Thanks.

-- 
tejun