From: ebiederm@xmission.com (Eric W. Biederman)
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>
References: <20110216185234.GA11636@tiehlicka.suse.cz>
	<20110216193700.GA6377@elte.hu>
	<AANLkTinDxxbVjrUViCs=UaMD9Wg9PR7b0ShNud5zKE3w@mail.gmail.com>
	<AANLkTi=xnbcs5BKj3cNE_aLtBO7W5m+2uaUacu7M8g_S@mail.gmail.com>
	<20110217090910.GA3781@tiehlicka.suse.cz>
	<AANLkTikPKpNHxDQAYBd3fiQsmVozLtCVDsNn=+eF_q2r@mail.gmail.com>
	<20110217163531.GF14168@elte.hu>
Date: Thu, 17 Feb 2011 10:57:54 -0800
In-Reply-To: <20110217163531.GF14168@elte.hu> (Ingo Molnar's message of "Thu,
	17 Feb 2011 17:35:31 +0100")
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Subject: Re: BUG: Bad page map in process udevd (anon_vma: (null)) in 2.6.38-rc4
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Ingo Molnar <mingo@elte.hu> writes:

> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> And in addition, I don't see why others wouldn't see it (I've got
>> DEBUG_PAGEALLOC and SLUB_DEBUG_ON turned on myself, and I know others
>> do too).
>
> I've done extensive randconfig testing and no crash triggers for typical workloads 
> on a typical dual-core PC. If there's a generic crashes in there my tests tend to 
> trigger them at least 10x as often as regular testers ;-) But the tests are still 
> only statistical so the race could simply be special and missed by the tests.
>
>> So I'm wondering what triggers it. Must be something subtle.
>
> I think what Michal did before he got the corruption seemed somewhat atypical: 
> suspend/resume and udevd wifi twiddling, right?
>
> Now, Eric's crashes look similar - and he does not seem to have done anything 
> special to trigger the crashes.
>
> Eric, could you possibly describe your system in a bit more detail, does it do 
> suspend and does the box use wifi actively? Anything atypical in your setup or usage 
> that doesnt match a bog-standard whitebox PC with LAN? Swap to file? NFS? FUSE? 
> Anything that is even just borderline atypical.

10G RAM
2G Swap
dual socket system
4 cores per socket
No hyperthreading.

fedora 14
ext4 on all filesystems

The biggest difference is I beat the system to death with automated builds.

I was about to say this happens with DEBUG_PAGEALLOC enabled but it
appears that options keeps eluding my fingers when I have a few minutes
to play with it.  Perhaps this time will be the charm.

The biggest difference may be that I am constantly stressing the system
to the edge of triggering the OOM killer.  My builds and tests are
greedy when it comes to memory.

I guess also I only see the bad PMD on processes that exit.  So it may
be that it is a matter of timing to see it.

Eric
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