cgroups: fix a css_set not found bug in cgroup_attach_proc
authorMandeep Singh Baines <msb@chromium.org>
Thu, 15 Dec 2011 19:36:43 +0000 (11:36 -0800)
committerRohan Somvanshi <rsomvanshi@nvidia.com>
Wed, 11 Jan 2012 17:52:46 +0000 (09:52 -0800)
commit2d5ebc34329444db7f46e54ec19d4dc8e60c102a
tree0eb1097afc1688562e3c0251783e5e0fe4fc8db5
parent0746a065d0f10996bae7422896eb885fbbcef393
cgroups: fix a css_set not found bug in cgroup_attach_proc

commit e0197aae59e55c06db172bfbe1a1cdb8c0e1cab3 upstream.

There is a BUG when migrating a PF_EXITING proc. Since css_set_prefetch()
is not called for the PF_EXITING case, find_existing_css_set() will return
NULL inside cgroup_task_migrate() causing a BUG.

This bug is easy to reproduce. Create a zombie and echo its pid to
cgroup.procs.

$ cat zombie.c
\#include <unistd.h>

int main()
{
  if (fork())
      pause();
  return 0;
}
$

We are hitting this bug pretty regularly on ChromeOS.

This bug is already fixed by Tejun Heo's cgroup patchset which is
targetted for the next merge window:

https://lkml.org/lkml/2011/11/1/356

I've create a smaller patch here which just fixes this bug so that a
fix can be merged into the current release and stable.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Downstream-Bug-Report: http://crosbug.com/23953
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: containers@lists.linux-foundation.org
Cc: cgroups@vger.kernel.org
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Olof Johansson <olofj@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Change-Id: I61bf2d48574d6ce5418b988e9547937c2efdd084
Reviewed-on: http://git-master/r/74185
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Rohan Somvanshi <rsomvanshi@nvidia.com>
Tested-by: Rohan Somvanshi <rsomvanshi@nvidia.com>
kernel/cgroup.c