linux-kernel - Re: [PATCH] mm: skip zombie in OOM-killer

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Date:	Mon, 7 Mar 2011 14:55:37 +0300
From:	Andrew Vagin <avagin@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: skip zombie in OOM-killer

2011/3/7 David Rientjes <rientjes@...gle.com>:
> On Sun, 6 Mar 2011, KOSAKI Motohiro wrote:
>
>> > When we check that task has flag TIF_MEMDIE, we forgot check that
>> > it has mm. A task may be zombie and a parent may wait a memor.
>> >
>> > v2: Check that task doesn't have mm one time and skip it immediately
>> >
>> > Signed-off-by: Andrey Vagin <avagin@...nvz.org>
>>
>> This seems incorrect. Do you have a reprodusable testcasae?
>> Your patch only care thread group leader state, but current code
>> care all thread in the process. Please look at oom_badness() and
>> find_lock_task_mm().
>>
>
> That's all irrelevant, the test for TIF_MEMDIE specifically makes the oom
> killer a complete no-op when an eligible task is found to have been oom
> killed to prevent needlessly killing additional tasks.  oom_badness() and
> find_lock_task_mm() have nothing to do with that check to return
> ERR_PTR(-1UL) from select_bad_process().
>
> Andrey is patching the case where an eligible TIF_MEMDIE process is found
> but it has already detached its ->mm.  In combination with the patch
> posted to linux-mm, oom: prevent unnecessary oom kills or kernel panics,
> which makes select_bad_process() iterate over all threads, it is an
> effective solution.

Probably you said about the first version of my patch.
This version is incorrect because of
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=dd8e8f405ca386c7ce7cbb996ccd985d283b0e03

but my first patch is correct and it has a simple reproducer(I
attached it). You can execute it and your kernel hangs up, because the
parent doesn't wait children, but the one child (zombie) will have
flag TIF_MEMDIE, oom_killer will kill nobody


The link on the first patch:
http://groups.google.com/group/linux.kernel/browse_thread/thread/b9c6ddf34d1671ab/2941e1877ca4f626?lnk=raot&pli=1
>
> Thanks.
> --
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Download attachment "memeater_killer.py" of type "application/octet-stream" (780 bytes)