I think this can be a fix.
maybe good to CC Oleg. 

==
>From dff52fb35af0cf36486965d19ee79e04b59f1dc4 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Date: Fri, 10 Jun 2011 13:15:14 +0900
Subject: [PATCH] [BUGFIX] update mm->owner even if no next owner.

A panic is reported.

> Call Trace:
>  [<ffffffff81139792>] mem_cgroup_from_task+0x15/0x17
>  [<ffffffff8113a75a>] __mem_cgroup_try_charge+0x148/0x4b4
>  [<ffffffff810493f3>] ? need_resched+0x23/0x2d
>  [<ffffffff814cbf43>] ? preempt_schedule+0x46/0x4f
>  [<ffffffff8113afe8>] mem_cgroup_charge_common+0x9a/0xce
>  [<ffffffff8113b6d1>] mem_cgroup_newpage_charge+0x5d/0x5f
>  [<ffffffff81134024>] khugepaged+0x5da/0xfaf
>  [<ffffffff81078ea0>] ? __init_waitqueue_head+0x4b/0x4b
>  [<ffffffff81133a4a>] ? add_mm_counter.constprop.5+0x13/0x13
>  [<ffffffff81078625>] kthread+0xa8/0xb0
>  [<ffffffff814d13e8>] ? sub_preempt_count+0xa1/0xb4
>  [<ffffffff814d5664>] kernel_thread_helper+0x4/0x10
>  [<ffffffff814ce858>] ? retint_restore_args+0x13/0x13
>  [<ffffffff8107857d>] ? __init_kthread_worker+0x5a/0x5a

The code is.
>         return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
>                                 struct mem_cgroup, css);


What happens here is accssing a freed task struct "p" from mm->owner.
So, it's doubtful that mm->owner points to freed task struct.