linux-kernel - Re: process hangs on do

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Date:	Tue, 23 Oct 2012 17:10:06 +0800
From:	Qiang Gao <gaoqiangscut@...il.com>
To:	Sha Zhengju <handai.szj@...il.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	linux-mm@...ck.org, bsingharora@...il.com
Subject: Re: process hangs on do_exit when oom happens

global-oom is the right thing to do. but oom-killed-process hanging on
do_exit is not the normal behavior

On Tue, Oct 23, 2012 at 5:01 PM, Sha Zhengju <handai.szj@...il.com> wrote:
> On 10/23/2012 11:35 AM, Qiang Gao wrote:
>>
>> information about the system is in the attach file "information.txt"
>>
>> I can not reproduce it in the upstream 3.6.0 kernel..
>>
>> On Sat, Oct 20, 2012 at 12:04 AM, Michal Hocko<mhocko@...e.cz>  wrote:
>>>
>>> On Wed 17-10-12 18:23:34, gaoqiang wrote:
>>>>
>>>> I looked up nothing useful with google,so I'm here for help..
>>>>
>>>> when this happens:  I use memcg to limit the memory use of a
>>>> process,and when the memcg cgroup was out of memory,
>>>> the process was oom-killed   however,it cannot really complete the
>>>> exiting. here is the some information
>>>
>>> How many tasks are in the group and what kind of memory do they use?
>>> Is it possible that you were hit by the same issue as described in
>>> 79dfdacc memcg: make oom_lock 0 and 1 based rather than counter.
>>>
>>>> OS version:  centos6.2    2.6.32.220.7.1
>>>
>>> Your kernel is quite old and you should be probably asking your
>>> distribution to help you out. There were many fixes since 2.6.32.
>>> Are you able to reproduce the same issue with the current vanila kernel?
>>>
>>>> /proc/pid/stack
>>>> ---------------------------------------------------------------
>>>>
>>>> [<ffffffff810597ca>] __cond_resched+0x2a/0x40
>>>> [<ffffffff81121569>] unmap_vmas+0xb49/0xb70
>>>> [<ffffffff8112822e>] exit_mmap+0x7e/0x140
>>>> [<ffffffff8105b078>] mmput+0x58/0x110
>>>> [<ffffffff81061aad>] exit_mm+0x11d/0x160
>>>> [<ffffffff81061c9d>] do_exit+0x1ad/0x860
>>>> [<ffffffff81062391>] do_group_exit+0x41/0xb0
>>>> [<ffffffff81077cd8>] get_signal_to_deliver+0x1e8/0x430
>>>> [<ffffffff8100a4c4>] do_notify_resume+0xf4/0x8b0
>>>> [<ffffffff8100b281>] int_signal+0x12/0x17
>>>> [<ffffffffffffffff>] 0xffffffffffffffff
>>>
>>> This looks strange because this is just an exit part which shouldn't
>>> deadlock or anything. Is this stack stable? Have you tried to take check
>>> it more times?
>>>
>
> Does the machine only have about 700M memory? I also find something
> in the log file:
>
> Node 0 DMA free:2772kB min:72kB low:88kB high:108kB present:15312kB..
> lowmem_reserve[]: 0 674 674 674
> Node 0 DMA32 free:*3172kB* min:3284kB low:4104kB high:4924kB
> present:690712kB ..
> lowmem_reserve[]: 0 0 0 0
> 0 pages in swap cache
> Swap cache stats: add 0, delete 0, find 0/0
> Free swap  = 0kB
> Total swap = 0kB
> 179184 pages RAM  ==>  179184 * 4 / 1024 = *700M*
> 6773 pages reserved
>
>
> Note that the free memory of DMA32(3172KB) is lower than min watermark,
> which means the global is under pressure now. What's more the swap is off,
> so the global oom is normal behavior.
>
>
> Thanks,
> Sha
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