linux-kernel - Re: mm allocation failure and hang when running xfstests generic/269 on xfs

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Date:   Thu, 2 Mar 2017 09:42:23 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Xiong Zhou <xzhou@...hat.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Christoph Hellwig <hch@...radead.org>, linux-xfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: mm allocation failure and hang when running xfstests generic/269
 on xfs

On Thu 02-03-17 12:17:47, Anshuman Khandual wrote:
> On 03/02/2017 10:49 AM, Xiong Zhou wrote:
> > On Wed, Mar 01, 2017 at 04:37:31PM -0800, Christoph Hellwig wrote:
> >> On Wed, Mar 01, 2017 at 12:46:34PM +0800, Xiong Zhou wrote:
> >>> Hi,
> >>>
> >>> It's reproduciable, not everytime though. Ext4 works fine.
> >> On ext4 fsstress won't run bulkstat because it doesn't exist.  Either
> >> way this smells like a MM issue to me as there were not XFS changes
> >> in that area recently.
> > Yap.
> > 
> > First bad commit:
> > 
> > commit 5d17a73a2ebeb8d1c6924b91e53ab2650fe86ffb
> > Author: Michal Hocko <mhocko@...e.com>
> > Date:   Fri Feb 24 14:58:53 2017 -0800
> > 
> >     vmalloc: back off when the current task is killed
> > 
> > Reverting this commit on top of
> >   e5d56ef Merge tag 'watchdog-for-linus-v4.11'
> > survives the tests.
> 
> Does fsstress test or the system hang ? I am not familiar with this
> code but If it's the test which is getting hung and its hitting this
> new check introduced by the above commit that means the requester is
> currently being killed by OOM killer for some other memory allocation
> request.

Well, not exactly. It is sufficient for it to be _killed_ by SIGKILL.
And for that it just needs to do a group_exit when one thread was still
in the kernel (see zap_process). While I can change this check to
actually do the oom specific check I believe a more generic
fatal_signal_pending is the right thing to do here. I am still not sure
what is the actual problem here, though. Could you be more specific
please?

-- 
Michal Hocko
SUSE Labs