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

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Date:   Thu, 2 Mar 2017 17:23:52 +0800
From:   Xiong Zhou <xzhou@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Xiong Zhou <xzhou@...hat.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        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, Mar 02, 2017 at 09:42:23AM +0100, Michal Hocko wrote:
> 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?

It's blocking the test and system-shutdown. fsstress wont exit.

For anyone interested, a simple ugly reproducer:

cat > fst.sh <<EOFF
#! /bin/bash -x

[ \$# -ne 3 ] && { echo "./single FSTYP TEST XFSTESTS_DIR"; exit 1; }

FST=\$1
BLKSZ=4096

fallocate -l 10G /home/test.img
fallocate -l 15G /home/scratch.img

MNT1=/loopmnt
MNT2=/loopsch

mkdir -p \$MNT1
mkdir -p \$MNT2

DEV1=\$(losetup --find --show /home/test.img)
DEV2=\$(losetup --find --show /home/scratch.img)

cleanup()
{
	umount -d \$MNT1
	umount -d \$MNT2
	umount \$DEV1 \$DEV2
	losetup -D || losetup -a | awk -F: '{print \$1}' | xargs losetup -d
	rm -f /home/{test,scratch}.img
}

trap cleanup 0 1 2

if [[ \$FST =~ ext ]] ; then
	mkfs.\${FST} -Fq -b \${BLKSZ} \$DEV1
elif [[ \$FST =~ xfs ]] ; then
	mkfs.\${FST} -fq -b size=\${BLKSZ} \$DEV1
fi
if test \$? -ne 0 ; then
	echo "mkfs \$DEV1 failed" 
	exit 1
fi

if [[ \$FST =~ ext ]] ; then
	mkfs.\${FST} -Fq -b \${BLKSZ} \$DEV2
elif [[ \$FST =~ xfs ]] ; then
	mkfs.\${FST} -fq -b size=\${BLKSZ} \$DEV2
fi
if test \$? -ne 0 ; then
	echo "mkfs \$DEV2 failed"
	exit 1
fi

mount \$DEV1 \$MNT1
if test \$? -ne 0 ; then
	echo "mount \$DEV1 failed" 
	exit 1
fi
mount \$DEV2 \$MNT2
if test \$? -ne 0 ; then
	echo "mount \$DEV2 failed" 
	exit 1
fi

pushd \$3 || exit 1

cat > local.config <<EOF
TEST_DEV=\$DEV1
TEST_DIR=\$MNT1
SCRATCH_MNT=\$MNT2
SCRATCH_DEV=\$DEV2
EOF

i=0
while [ \$i -lt 50 ] ; do
	./check \$2
	echo \$i
	((i=\$i+1))
done

popd
EOFF

git clone git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
cd xfstests-dev
make -j2 && make install || exit 1
cd -
sh -x ./fst.sh xfs generic/269 xfstests-dev


> -- 
> Michal Hocko
> SUSE Labs