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

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  Re: mm allocation failure and hang when running xfstests generic/269  on xfs Christoph Hellwig <hch@infradead.org> - 2017-03-02 01:40 +0100
    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Xiong Zhou <xzhou@redhat.com> - 2017-03-02 06:40 +0100
      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-03-02 07:50 +0100
        Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 09:50 +0100
          Re: mm allocation failure and hang when running xfstests generic/269  on xfs Xiong Zhou <xzhou@redhat.com> - 2017-03-02 10:30 +0100
      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Bob Liu <liubo95@huawei.com> - 2017-03-02 07:50 +0100
      Re: mm allocation failure and hang when running xfstests generic/269on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 12:50 +0100
      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 13:00 +0100
        Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 13:30 +0100
          Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 13:30 +0100
            Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 14:10 +0100
              Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 15:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 15:00 +0100
                  Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:00 +0100
                    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:40 +0100
                      [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-02 16:50 +0100
                        [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is killed Michal Hocko <mhocko@kernel.org> - 2017-03-02 16:50 +0100
                          Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task         is killed Christoph Hellwig <hch@lst.de> - 2017-03-02 17:00 +0100
                          Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is  killed Brian Foster <bfoster@redhat.com> - 2017-03-02 17:10 +0100
                        Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Brian Foster <bfoster@redhat.com> - 2017-03-02 17:10 +0100
                        Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Christoph Hellwig <hch@lst.de> - 2017-03-02 17:20 +0100
                        Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-02 17:40 +0100
                          Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-03-02 17:50 +0100
                        Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Dave Chinner <david@fromorbit.com> - 2017-03-04 00:00 +0100
                          Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-03-04 00:30 +0100
                            Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Dave Chinner <david@fromorbit.com> - 2017-03-04 05:50 +0100
                          Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-06 14:30 +0100
                      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 20:20 +0100
                    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Christoph Hellwig <hch@infradead.org> - 2017-03-02 19:00 +0100
                    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 20:20 +0100
                  Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:00 +0100
                    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 18:40 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 15:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 15:10 +0100
                Re: mm allocation failure and hang when running xfstests generic/269 on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 17:00 +0100

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#1590737 — Re: mm allocation failure and hang when running xfstests generic/269 on xfs

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.

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#1590849

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@suse.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.

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#1590866

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@suse.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. Then is not this kind if memory alloc failure expected ?

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#1590922

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@suse.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

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#1590943

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@suse.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

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#1590868

On 2017/3/2 13:19, 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:
> 

It looks like not a bug.
From below commit, the allocation failure print was due to current process received SIGKILL signal.
You may need to confirm whether that's the case. 

Regards,
Bob

> commit 5d17a73a2ebeb8d1c6924b91e53ab2650fe86ffb
> Author: Michal Hocko <mhocko@suse.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.
> 

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#1591015 — Re: mm allocation failure and hang when running xfstests generic/269on xfs

Michal Hocko wrote:
> On Thu 02-03-17 19:04:48, Tetsuo Handa wrote:
> [...]
> > So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
> > killed") implemented __GFP_KILLABLE flag and automatically applied that
> > flag. As a result, those who are not ready to fail upon SIGKILL are
> > confused. ;-)
> 
> You are right! The function is documented it might fail but the code
> doesn't really allow that. This seems like a bug to me. What do you
> think about the following?

Yes, I think this patch is correct. Maybe

-May fail and may return vmalloced memory.
+May fail.

together, for it is always vmalloc()ed memory.

> ---
> From d02cb0285d8ce3344fd64dc7e2912e9a04bef80d Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Thu, 2 Mar 2017 11:31:11 +0100
> Subject: [PATCH] xfs: allow kmem_zalloc_greedy to fail
> 
> Even though kmem_zalloc_greedy is documented it might fail the current
> code doesn't really implement this properly and loops on the smallest
> allowed size for ever. This is a problem because vzalloc might fail
> permanently. Since 5d17a73a2ebe ("vmalloc: back off when the current
> task is killed") such a failure is much more probable than it used to
> be. Fix this by bailing out if the minimum size request failed.
> 
> This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> 
> Reported-by: Xiong Zhou <xzhou@redhat.com>
> Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  fs/xfs/kmem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 339c696bbc01..ee95f5c6db45 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
>  	size_t		kmsize = maxsize;
>  
>  	while (!(ptr = vzalloc(kmsize))) {
> +		if (kmsize == minsize)
> +			break;
>  		if ((kmsize >>= 1) <= minsize)
>  			kmsize = minsize;
>  	}
> -- 
> 2.11.0
> 
> -- 
> Michal Hocko
> SUSE Labs
> 

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#1591016

On 2017/03/02 14:19, 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@suse.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.
> 

Looks like kmem_zalloc_greedy() is broken.
It loops forever until vzalloc() succeeds.
If somebody (not limited to the OOM killer) sends SIGKILL and
vmalloc() backs off, kmem_zalloc_greedy() will loop forever.

----------------------------------------
void *
kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
{
        void            *ptr;
        size_t          kmsize = maxsize;

        while (!(ptr = vzalloc(kmsize))) {
                if ((kmsize >>= 1) <= minsize)
                        kmsize = minsize;
        }
        if (ptr)
                *size = kmsize;
        return ptr;
}
----------------------------------------

So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
killed") implemented __GFP_KILLABLE flag and automatically applied that
flag. As a result, those who are not ready to fail upon SIGKILL are
confused. ;-)

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#1591026

On Thu 02-03-17 19:04:48, Tetsuo Handa wrote:
[...]
> So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
> killed") implemented __GFP_KILLABLE flag and automatically applied that
> flag. As a result, those who are not ready to fail upon SIGKILL are
> confused. ;-)

You are right! The function is documented it might fail but the code
doesn't really allow that. This seems like a bug to me. What do you
think about the following?
---
From d02cb0285d8ce3344fd64dc7e2912e9a04bef80d Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Thu, 2 Mar 2017 11:31:11 +0100
Subject: [PATCH] xfs: allow kmem_zalloc_greedy to fail

Even though kmem_zalloc_greedy is documented it might fail the current
code doesn't really implement this properly and loops on the smallest
allowed size for ever. This is a problem because vzalloc might fail
permanently. Since 5d17a73a2ebe ("vmalloc: back off when the current
task is killed") such a failure is much more probable than it used to
be. Fix this by bailing out if the minimum size request failed.

This has been noticed by a hung generic/269 xfstest by Xiong Zhou.

Reported-by: Xiong Zhou <xzhou@redhat.com>
Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 fs/xfs/kmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 339c696bbc01..ee95f5c6db45 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
 	size_t		kmsize = maxsize;
 
 	while (!(ptr = vzalloc(kmsize))) {
+		if (kmsize == minsize)
+			break;
 		if ((kmsize >>= 1) <= minsize)
 			kmsize = minsize;
 	}
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs

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#1591028

On Thu, Mar 02, 2017 at 11:35:20AM +0100, Michal Hocko wrote:
> On Thu 02-03-17 19:04:48, Tetsuo Handa wrote:
> [...]
> > So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
> > killed") implemented __GFP_KILLABLE flag and automatically applied that
> > flag. As a result, those who are not ready to fail upon SIGKILL are
> > confused. ;-)
> 
> You are right! The function is documented it might fail but the code
> doesn't really allow that. This seems like a bug to me. What do you
> think about the following?
> ---
> From d02cb0285d8ce3344fd64dc7e2912e9a04bef80d Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Thu, 2 Mar 2017 11:31:11 +0100
> Subject: [PATCH] xfs: allow kmem_zalloc_greedy to fail
> 
> Even though kmem_zalloc_greedy is documented it might fail the current
> code doesn't really implement this properly and loops on the smallest
> allowed size for ever. This is a problem because vzalloc might fail
> permanently. Since 5d17a73a2ebe ("vmalloc: back off when the current
> task is killed") such a failure is much more probable than it used to
> be. Fix this by bailing out if the minimum size request failed.
> 
> This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> 
> Reported-by: Xiong Zhou <xzhou@redhat.com>
> Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  fs/xfs/kmem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 339c696bbc01..ee95f5c6db45 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
>  	size_t		kmsize = maxsize;
>  
>  	while (!(ptr = vzalloc(kmsize))) {
> +		if (kmsize == minsize)
> +			break;
>  		if ((kmsize >>= 1) <= minsize)
>  			kmsize = minsize;
>  	}

More consistent with the rest of the kmem code might be to accept a
flags argument and do something like this based on KM_MAYFAIL. The one
current caller looks like it would pass it, but I suppose we'd still
need a mechanism to break out should a new caller not pass that flag.
Would a fatal_signal_pending() check in the loop as well allow us to
break out in the scenario that is reproduced here?

Brian

> -- 
> 2.11.0
> 
> -- 
> Michal Hocko
> SUSE Labs
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

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#1591056

On Thu 02-03-17 07:24:27, Brian Foster wrote:
> On Thu, Mar 02, 2017 at 11:35:20AM +0100, Michal Hocko wrote:
> > On Thu 02-03-17 19:04:48, Tetsuo Handa wrote:
> > [...]
> > > So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
> > > killed") implemented __GFP_KILLABLE flag and automatically applied that
> > > flag. As a result, those who are not ready to fail upon SIGKILL are
> > > confused. ;-)
> > 
> > You are right! The function is documented it might fail but the code
> > doesn't really allow that. This seems like a bug to me. What do you
> > think about the following?
> > ---
> > From d02cb0285d8ce3344fd64dc7e2912e9a04bef80d Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@suse.com>
> > Date: Thu, 2 Mar 2017 11:31:11 +0100
> > Subject: [PATCH] xfs: allow kmem_zalloc_greedy to fail
> > 
> > Even though kmem_zalloc_greedy is documented it might fail the current
> > code doesn't really implement this properly and loops on the smallest
> > allowed size for ever. This is a problem because vzalloc might fail
> > permanently. Since 5d17a73a2ebe ("vmalloc: back off when the current
> > task is killed") such a failure is much more probable than it used to
> > be. Fix this by bailing out if the minimum size request failed.
> > 
> > This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> > 
> > Reported-by: Xiong Zhou <xzhou@redhat.com>
> > Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> >  fs/xfs/kmem.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> > index 339c696bbc01..ee95f5c6db45 100644
> > --- a/fs/xfs/kmem.c
> > +++ b/fs/xfs/kmem.c
> > @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
> >  	size_t		kmsize = maxsize;
> >  
> >  	while (!(ptr = vzalloc(kmsize))) {
> > +		if (kmsize == minsize)
> > +			break;
> >  		if ((kmsize >>= 1) <= minsize)
> >  			kmsize = minsize;
> >  	}
> 
> More consistent with the rest of the kmem code might be to accept a
> flags argument and do something like this based on KM_MAYFAIL.

Well, vmalloc doesn't really support GFP_NOFAIL semantic right now for
the same reason it doesn't support GFP_NOFS. So I am not sure this is a
good idea.

> The one
> current caller looks like it would pass it, but I suppose we'd still
> need a mechanism to break out should a new caller not pass that flag.
> Would a fatal_signal_pending() check in the loop as well allow us to
> break out in the scenario that is reproduced here?

Yes that check would work as well I just thought the break out when the
minsize request fails to be more logical. There might be other reasons
to fail the request and looping here seems just wrong. But whatever you
or other xfs people prefer.
-- 
Michal Hocko
SUSE Labs

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#1591095

On Thu, Mar 02, 2017 at 01:49:09PM +0100, Michal Hocko wrote:
> On Thu 02-03-17 07:24:27, Brian Foster wrote:
> > On Thu, Mar 02, 2017 at 11:35:20AM +0100, Michal Hocko wrote:
> > > On Thu 02-03-17 19:04:48, Tetsuo Handa wrote:
> > > [...]
> > > > So, commit 5d17a73a2ebeb8d1("vmalloc: back off when the current task is
> > > > killed") implemented __GFP_KILLABLE flag and automatically applied that
> > > > flag. As a result, those who are not ready to fail upon SIGKILL are
> > > > confused. ;-)
> > > 
> > > You are right! The function is documented it might fail but the code
> > > doesn't really allow that. This seems like a bug to me. What do you
> > > think about the following?
> > > ---
> > > From d02cb0285d8ce3344fd64dc7e2912e9a04bef80d Mon Sep 17 00:00:00 2001
> > > From: Michal Hocko <mhocko@suse.com>
> > > Date: Thu, 2 Mar 2017 11:31:11 +0100
> > > Subject: [PATCH] xfs: allow kmem_zalloc_greedy to fail
> > > 
> > > Even though kmem_zalloc_greedy is documented it might fail the current
> > > code doesn't really implement this properly and loops on the smallest
> > > allowed size for ever. This is a problem because vzalloc might fail
> > > permanently. Since 5d17a73a2ebe ("vmalloc: back off when the current
> > > task is killed") such a failure is much more probable than it used to
> > > be. Fix this by bailing out if the minimum size request failed.
> > > 
> > > This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> > > 
> > > Reported-by: Xiong Zhou <xzhou@redhat.com>
> > > Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > > ---
> > >  fs/xfs/kmem.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> > > index 339c696bbc01..ee95f5c6db45 100644
> > > --- a/fs/xfs/kmem.c
> > > +++ b/fs/xfs/kmem.c
> > > @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
> > >  	size_t		kmsize = maxsize;
> > >  
> > >  	while (!(ptr = vzalloc(kmsize))) {
> > > +		if (kmsize == minsize)
> > > +			break;
> > >  		if ((kmsize >>= 1) <= minsize)
> > >  			kmsize = minsize;
> > >  	}
> > 
> > More consistent with the rest of the kmem code might be to accept a
> > flags argument and do something like this based on KM_MAYFAIL.
> 
> Well, vmalloc doesn't really support GFP_NOFAIL semantic right now for
> the same reason it doesn't support GFP_NOFS. So I am not sure this is a
> good idea.
> 

Not sure I follow..? I'm just suggesting to control the loop behavior
based on the KM_ flag, not to do or change anything wrt to GFP_ flags.

> > The one
> > current caller looks like it would pass it, but I suppose we'd still
> > need a mechanism to break out should a new caller not pass that flag.
> > Would a fatal_signal_pending() check in the loop as well allow us to
> > break out in the scenario that is reproduced here?
> 
> Yes that check would work as well I just thought the break out when the
> minsize request fails to be more logical. There might be other reasons
> to fail the request and looping here seems just wrong. But whatever you
> or other xfs people prefer.

There may be higher level reasons for why this code should or should not
loop, that just seems like a separate issue to me. My thinking is more
that this appears to be how every kmem_*() function operates today and
it seems a bit out of place to change behavior of one to fix a bug.

Maybe I'm missing something though.. are we subject to the same general
problem in any of the other kmem_*() functions that can currently loop
indefinitely?

Brian

> -- 
> Michal Hocko
> SUSE Labs

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#1591100

On Thu 02-03-17 08:41:58, Brian Foster wrote:
> On Thu, Mar 02, 2017 at 02:27:55PM +0100, Michal Hocko wrote:
[...]
> > I see your argument about being in sync with other kmem helpers but
> > those are bit different because regular page/slab allocators allow never
> > fail semantic (even though this is mostly ignored by those helpers which
> > implement their own retries but that is a different topic).
> > 
> 
> ... but what I'm trying to understand here is whether this failure
> scenario is specific to vmalloc() or whether the other kmem_*()
> functions are susceptible to the same problem. For example, suppose we
> replaced this kmem_zalloc_greedy() call with a kmem_zalloc(PAGE_SIZE,
> KM_SLEEP) call. Could we hit the same problem if the process is killed?

Well, kmem_zalloc uses kmalloc which can also fail when we are out of
memory but in that case we can expect the OOM killer releasing some
memory which would allow us to make a forward progress on the next
retry. So essentially retrying around kmalloc is much more safe in this
regard. Failing vmalloc might be permanent because there is no vmalloc
space to allocate from or much more likely due to already mentioned
patch. So vmalloc is different, really.
-- 
Michal Hocko
SUSE Labs

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#1591150

On Thu, Mar 02, 2017 at 03:34:41PM +0100, Michal Hocko wrote:
> On Thu 02-03-17 09:23:15, Brian Foster wrote:
> > On Thu, Mar 02, 2017 at 02:50:01PM +0100, Michal Hocko wrote:
> > > On Thu 02-03-17 08:41:58, Brian Foster wrote:
> > > > On Thu, Mar 02, 2017 at 02:27:55PM +0100, Michal Hocko wrote:
> > > [...]
> > > > > I see your argument about being in sync with other kmem helpers but
> > > > > those are bit different because regular page/slab allocators allow never
> > > > > fail semantic (even though this is mostly ignored by those helpers which
> > > > > implement their own retries but that is a different topic).
> > > > > 
> > > > 
> > > > ... but what I'm trying to understand here is whether this failure
> > > > scenario is specific to vmalloc() or whether the other kmem_*()
> > > > functions are susceptible to the same problem. For example, suppose we
> > > > replaced this kmem_zalloc_greedy() call with a kmem_zalloc(PAGE_SIZE,
> > > > KM_SLEEP) call. Could we hit the same problem if the process is killed?
> > > 
> > > Well, kmem_zalloc uses kmalloc which can also fail when we are out of
> > > memory but in that case we can expect the OOM killer releasing some
> > > memory which would allow us to make a forward progress on the next
> > > retry. So essentially retrying around kmalloc is much more safe in this
> > > regard. Failing vmalloc might be permanent because there is no vmalloc
> > > space to allocate from or much more likely due to already mentioned
> > > patch. So vmalloc is different, really.
> > 
> > Right.. that's why I'm asking. So it's technically possible but highly
> > unlikely due to the different failure characteristics. That seems
> > reasonable to me, then. 
> > 
> > To be clear, do we understand what causes the vzalloc() failure to be
> > effectively permanent in this specific reproducer? I know you mention
> > above that we could be out of vmalloc space, but that doesn't clarify
> > whether there are other potential failure paths or then what this has to
> > do with the fact that the process was killed. Does the pending signal
> > cause the subsequent failures or are you saying that there is some other
> > root cause of the failure, this process would effectively be spinning
> > here anyways, and we're just noticing it because it's trying to exit?
> 
> In this particular case it is fatal_signal_pending that causes the
> permanent failure. This check has been added to prevent from complete
> memory reserves depletion on OOM when a killed task has a free ticket to
> reserves and vmalloc requests can be really large. In this case there
> was no OOM killer going on but fsstress has SIGKILL pending for other
> reason. Most probably as a result of the group_exit when all threads
> are killed (see zap_process). I could have turn fatal_signal_pending
> into tsk_is_oom_victim which would be less likely to hit but in
> principle fatal_signal_pending should be better because we do want to
> bail out when the process is existing as soon as possible.
> 
> What I really wanted to say is that there are other possible permanent
> failure paths in vmalloc AFAICS. They are much less probable but they
> still exist.
> 
> Does that make more sense now?

Yes, thanks. That explains why this crops up now where it hasn't in the
past. Please include that background in the commit log description.

Also, that kind of makes me think that a fatal_signal_pending() check is
still appropriate in the loop, even if we want to drop the infinite
retry loop in kmem_zalloc_greedy() as well. There's no sense in doing
however many retries are left before we return and that's also more
explicit for the next person who goes to change this code in the future.

Otherwise, I'm fine with breaking the infinite retry loop at the same
time. It looks like Christoph added this function originally so this
should probably require his ack as well..

Brian

> -- 
> Michal Hocko
> SUSE Labs
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

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#1591194

On Thu, Mar 02, 2017 at 04:14:11PM +0100, Michal Hocko wrote:
> On Thu 02-03-17 09:51:31, Brian Foster wrote:
> > On Thu, Mar 02, 2017 at 03:34:41PM +0100, Michal Hocko wrote:
> > > On Thu 02-03-17 09:23:15, Brian Foster wrote:
> > > > On Thu, Mar 02, 2017 at 02:50:01PM +0100, Michal Hocko wrote:
> > > > > On Thu 02-03-17 08:41:58, Brian Foster wrote:
> > > > > > On Thu, Mar 02, 2017 at 02:27:55PM +0100, Michal Hocko wrote:
> > > > > [...]
> > > > > > > I see your argument about being in sync with other kmem helpers but
> > > > > > > those are bit different because regular page/slab allocators allow never
> > > > > > > fail semantic (even though this is mostly ignored by those helpers which
> > > > > > > implement their own retries but that is a different topic).
> > > > > > > 
> > > > > > 
> > > > > > ... but what I'm trying to understand here is whether this failure
> > > > > > scenario is specific to vmalloc() or whether the other kmem_*()
> > > > > > functions are susceptible to the same problem. For example, suppose we
> > > > > > replaced this kmem_zalloc_greedy() call with a kmem_zalloc(PAGE_SIZE,
> > > > > > KM_SLEEP) call. Could we hit the same problem if the process is killed?
> > > > > 
> > > > > Well, kmem_zalloc uses kmalloc which can also fail when we are out of
> > > > > memory but in that case we can expect the OOM killer releasing some
> > > > > memory which would allow us to make a forward progress on the next
> > > > > retry. So essentially retrying around kmalloc is much more safe in this
> > > > > regard. Failing vmalloc might be permanent because there is no vmalloc
> > > > > space to allocate from or much more likely due to already mentioned
> > > > > patch. So vmalloc is different, really.
> > > > 
> > > > Right.. that's why I'm asking. So it's technically possible but highly
> > > > unlikely due to the different failure characteristics. That seems
> > > > reasonable to me, then. 
> > > > 
> > > > To be clear, do we understand what causes the vzalloc() failure to be
> > > > effectively permanent in this specific reproducer? I know you mention
> > > > above that we could be out of vmalloc space, but that doesn't clarify
> > > > whether there are other potential failure paths or then what this has to
> > > > do with the fact that the process was killed. Does the pending signal
> > > > cause the subsequent failures or are you saying that there is some other
> > > > root cause of the failure, this process would effectively be spinning
> > > > here anyways, and we're just noticing it because it's trying to exit?
> > > 
> > > In this particular case it is fatal_signal_pending that causes the
> > > permanent failure. This check has been added to prevent from complete
> > > memory reserves depletion on OOM when a killed task has a free ticket to
> > > reserves and vmalloc requests can be really large. In this case there
> > > was no OOM killer going on but fsstress has SIGKILL pending for other
> > > reason. Most probably as a result of the group_exit when all threads
> > > are killed (see zap_process). I could have turn fatal_signal_pending
> > > into tsk_is_oom_victim which would be less likely to hit but in
> > > principle fatal_signal_pending should be better because we do want to
> > > bail out when the process is existing as soon as possible.
> > > 
> > > What I really wanted to say is that there are other possible permanent
> > > failure paths in vmalloc AFAICS. They are much less probable but they
> > > still exist.
> > > 
> > > Does that make more sense now?
> > 
> > Yes, thanks. That explains why this crops up now where it hasn't in the
> > past. Please include that background in the commit log description.
> 
> OK, does this sound better. I am open to any suggestions to improve this
> of course
> 

Yeah..

> : xfs: allow kmem_zalloc_greedy to fail
> : 
> : Even though kmem_zalloc_greedy is documented it might fail the current
> : code doesn't really implement this properly and loops on the smallest
> : allowed size for ever. This is a problem because vzalloc might fail
> : permanently - we might run out of vmalloc space or since 5d17a73a2ebe
> : ("vmalloc: back off when the current task is killed") when the current
> : task is killed. The later one makes the failure scenario much more
> : probable than it used to be. Fix this by bailing out if the minimum size
                               ^
	" because it makes vmalloc() failures permanent for tasks with fatal
	  signals pending."

> : request failed.
> : 
> : This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> : 
> : fsstress: vmalloc: allocation failure, allocated 12288 of 20480 bytes, mode:0x14080c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO), nodemask=(null)
> : fsstress cpuset=/ mems_allowed=0-1
> : CPU: 1 PID: 23460 Comm: fsstress Not tainted 4.10.0-master-45554b2+ #21
> : Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/05/2016
> : Call Trace:
> :  dump_stack+0x63/0x87
> :  warn_alloc+0x114/0x1c0
> :  ? alloc_pages_current+0x88/0x120
> :  __vmalloc_node_range+0x250/0x2a0
> :  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
> :  ? free_hot_cold_page+0x21f/0x280
> :  vzalloc+0x54/0x60
> :  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
> :  kmem_zalloc_greedy+0x2b/0x40 [xfs]
> :  xfs_bulkstat+0x11b/0x730 [xfs]
> :  ? xfs_bulkstat_one_int+0x340/0x340 [xfs]
> :  ? selinux_capable+0x20/0x30
> :  ? security_capable+0x48/0x60
> :  xfs_ioc_bulkstat+0xe4/0x190 [xfs]
> :  xfs_file_ioctl+0x9dd/0xad0 [xfs]
> :  ? do_filp_open+0xa5/0x100
> :  do_vfs_ioctl+0xa7/0x5e0
> :  SyS_ioctl+0x79/0x90
> :  do_syscall_64+0x67/0x180
> :  entry_SYSCALL64_slow_path+0x25/0x25
> : 
> : fsstress keeps looping inside kmem_zalloc_greedy without any way out
> : because vmalloc keeps failing due to fatal_signal_pending.
> : 
> : Reported-by: Xiong Zhou <xzhou@redhat.com>
> : Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> : Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> > Also, that kind of makes me think that a fatal_signal_pending() check is
> > still appropriate in the loop, even if we want to drop the infinite
> > retry loop in kmem_zalloc_greedy() as well. There's no sense in doing
> > however many retries are left before we return and that's also more
> > explicit for the next person who goes to change this code in the future.
> 
> I am not objecting to adding fatal_signal_pending as well I just thought
> that from the logic POV breaking after reaching the minimum size is just
> the right thing to do. We can optimize further by checking
> fatal_signal_pending and reducing retries when we know it doesn't make
> much sense but that should be done on top as an optimization IMHO.
> 

I don't think of it as an optimization to not invoke calls (a
non-deterministic number of times) that we know are going to fail, but
ultimately I don't care too much how it's framed or if it's done in
separate patches or whatnot. As long as they are posted at the same
time. ;)

Brian

> > Otherwise, I'm fine with breaking the infinite retry loop at the same
> > time. It looks like Christoph added this function originally so this
> > should probably require his ack as well..
> 
> What do you think Christoph?
> -- 
> Michal Hocko
> SUSE Labs

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#1591205 — [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

From: Michal Hocko <mhocko@suse.com>

Even though kmem_zalloc_greedy is documented it might fail the current
code doesn't really implement this properly and loops on the smallest
allowed size for ever. This is a problem because vzalloc might fail
permanently - we might run out of vmalloc space or since 5d17a73a2ebe
("vmalloc: back off when the current task is killed") when the current
task is killed. The later one makes the failure scenario much more
probable than it used to be because it makes vmalloc() failures
permanent for tasks with fatal signals pending.. Fix this by bailing out
if the minimum size request failed.

This has been noticed by a hung generic/269 xfstest by Xiong Zhou.

fsstress: vmalloc: allocation failure, allocated 12288 of 20480 bytes, mode:0x14080c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO), nodemask=(null)
fsstress cpuset=/ mems_allowed=0-1
CPU: 1 PID: 23460 Comm: fsstress Not tainted 4.10.0-master-45554b2+ #21
Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/05/2016
Call Trace:
 dump_stack+0x63/0x87
 warn_alloc+0x114/0x1c0
 ? alloc_pages_current+0x88/0x120
 __vmalloc_node_range+0x250/0x2a0
 ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
 ? free_hot_cold_page+0x21f/0x280
 vzalloc+0x54/0x60
 ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
 kmem_zalloc_greedy+0x2b/0x40 [xfs]
 xfs_bulkstat+0x11b/0x730 [xfs]
 ? xfs_bulkstat_one_int+0x340/0x340 [xfs]
 ? selinux_capable+0x20/0x30
 ? security_capable+0x48/0x60
 xfs_ioc_bulkstat+0xe4/0x190 [xfs]
 xfs_file_ioctl+0x9dd/0xad0 [xfs]
 ? do_filp_open+0xa5/0x100
 do_vfs_ioctl+0xa7/0x5e0
 SyS_ioctl+0x79/0x90
 do_syscall_64+0x67/0x180
 entry_SYSCALL64_slow_path+0x25/0x25

fsstress keeps looping inside kmem_zalloc_greedy without any way out
because vmalloc keeps failing due to fatal_signal_pending.

Reported-by: Xiong Zhou <xzhou@redhat.com>
Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 fs/xfs/kmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 339c696bbc01..ee95f5c6db45 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
 	size_t		kmsize = maxsize;
 
 	while (!(ptr = vzalloc(kmsize))) {
+		if (kmsize == minsize)
+			break;
 		if ((kmsize >>= 1) <= minsize)
 			kmsize = minsize;
 	}
-- 
2.11.0

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#1591208 — [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is killed

From: Michal Hocko <mhocko@suse.com>

It doesn't really make much sense to retry vmalloc request if the
current task is killed. We should rather bail out as soon as possible
and let it RIP as soon as possible. The current implementation of
vmalloc will fail anyway.

Suggested-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 fs/xfs/kmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index ee95f5c6db45..01c52567a4ff 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -34,7 +34,7 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
 	size_t		kmsize = maxsize;
 
 	while (!(ptr = vzalloc(kmsize))) {
-		if (kmsize == minsize)
+		if (kmsize == minsize || fatal_signal_pending(current))
 			break;
 		if ((kmsize >>= 1) <= minsize)
 			kmsize = minsize;
-- 
2.11.0

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#1591222 — Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is killed

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>

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#1591235 — Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is killed

On Thu, Mar 02, 2017 at 04:45:41PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> It doesn't really make much sense to retry vmalloc request if the
> current task is killed. We should rather bail out as soon as possible
> and let it RIP as soon as possible. The current implementation of
> vmalloc will fail anyway.
> 
> Suggested-by: Brian Foster <bfoster@redhat.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/kmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index ee95f5c6db45..01c52567a4ff 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -34,7 +34,7 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
>  	size_t		kmsize = maxsize;
>  
>  	while (!(ptr = vzalloc(kmsize))) {
> -		if (kmsize == minsize)
> +		if (kmsize == minsize || fatal_signal_pending(current))
>  			break;
>  		if ((kmsize >>= 1) <= minsize)
>  			kmsize = minsize;
> -- 
> 2.11.0
> 
> --
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#1591240 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

On Thu, Mar 02, 2017 at 04:45:40PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> Even though kmem_zalloc_greedy is documented it might fail the current
> code doesn't really implement this properly and loops on the smallest
> allowed size for ever. This is a problem because vzalloc might fail
> permanently - we might run out of vmalloc space or since 5d17a73a2ebe
> ("vmalloc: back off when the current task is killed") when the current
> task is killed. The later one makes the failure scenario much more
> probable than it used to be because it makes vmalloc() failures
> permanent for tasks with fatal signals pending.. Fix this by bailing out
> if the minimum size request failed.
> 
> This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> 
> fsstress: vmalloc: allocation failure, allocated 12288 of 20480 bytes, mode:0x14080c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO), nodemask=(null)
> fsstress cpuset=/ mems_allowed=0-1
> CPU: 1 PID: 23460 Comm: fsstress Not tainted 4.10.0-master-45554b2+ #21
> Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/05/2016
> Call Trace:
>  dump_stack+0x63/0x87
>  warn_alloc+0x114/0x1c0
>  ? alloc_pages_current+0x88/0x120
>  __vmalloc_node_range+0x250/0x2a0
>  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  ? free_hot_cold_page+0x21f/0x280
>  vzalloc+0x54/0x60
>  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  xfs_bulkstat+0x11b/0x730 [xfs]
>  ? xfs_bulkstat_one_int+0x340/0x340 [xfs]
>  ? selinux_capable+0x20/0x30
>  ? security_capable+0x48/0x60
>  xfs_ioc_bulkstat+0xe4/0x190 [xfs]
>  xfs_file_ioctl+0x9dd/0xad0 [xfs]
>  ? do_filp_open+0xa5/0x100
>  do_vfs_ioctl+0xa7/0x5e0
>  SyS_ioctl+0x79/0x90
>  do_syscall_64+0x67/0x180
>  entry_SYSCALL64_slow_path+0x25/0x25
> 
> fsstress keeps looping inside kmem_zalloc_greedy without any way out
> because vmalloc keeps failing due to fatal_signal_pending.
> 
> Reported-by: Xiong Zhou <xzhou@redhat.com>
> Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/kmem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 339c696bbc01..ee95f5c6db45 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
>  	size_t		kmsize = maxsize;
>  
>  	while (!(ptr = vzalloc(kmsize))) {
> +		if (kmsize == minsize)
> +			break;
>  		if ((kmsize >>= 1) <= minsize)
>  			kmsize = minsize;
>  	}
> -- 
> 2.11.0
> 
> --
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