On Fri, 10 Jun 2011 13:21:46 +0800
Xiaotian Feng [off-list ref] wrote:

On Fri, Jun 10, 2011 at 12:30 PM, KAMEZAWA Hiroyuki <
kamezawa.hiroyu@jp.fujitsu.com> wrote:

quoted

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

==

quoted

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

A panic is reported.

quoted

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.

quoted

        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.

But from the bug itself, it looks more likely kernel is hitting a freed
p->cgroups, right?
If p is already freed, the kernel will fault on
781cc62d: 8b 82 fc 08 00 00       mov    0x8fc(%edx),%eax

Then you will not get a value of 6b6b6b87, right?

%edx here is a pointer for task struct.
Then, task->cgroup == 0x6b6b6b6b. It means "task" is freed.

Thanks,
-Kame




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