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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

Page 2 of 2 — ← Prev page 1 [2]

#1591256 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

Looks fine,

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

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#1591265 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

I've just realized that Darrick was not on the CC list. Let's add him.
I believe this patch should go in in the current cycle because
5d17a73a2ebe was merged in this merge window and it can be abused...

The other patch [1] is not that urgent.

[1] http://lkml.kernel.org/r/20170302154541.16155-2-mhocko@kernel.org

On Thu 02-03-17 16:45:40, 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>
> ---
>  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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#1591280 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

On Thu, Mar 02, 2017 at 05:16:06PM +0100, Michal Hocko wrote:
> I've just realized that Darrick was not on the CC list. Let's add him.
> I believe this patch should go in in the current cycle because
> 5d17a73a2ebe was merged in this merge window and it can be abused...
> 
> The other patch [1] is not that urgent.
> 
> [1] http://lkml.kernel.org/r/20170302154541.16155-2-mhocko@kernel.org

Both patches look ok to me.  I'll take both patches for rc2.
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

(Annoyingly I missed the whole thread yesterday due to vger slowness, in
case anyone was wondering why I didn't reply.)

--D

> 
> On Thu 02-03-17 16:45:40, 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>
> > ---
> >  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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

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#1592329 — 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>
> ---
>  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;
>  	}

Seems wrong to me - this function used to have lots of callers and
over time we've slowly removed them or replaced them with something
else. I'd suggest removing it completely, replacing the call sites
with kmem_zalloc_large().

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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#1592339 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

On Sat, Mar 04, 2017 at 09:54:44AM +1100, Dave Chinner wrote:
> 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>
> > ---
> >  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;
> >  	}
> 
> Seems wrong to me - this function used to have lots of callers and
> over time we've slowly removed them or replaced them with something
> else. I'd suggest removing it completely, replacing the call sites
> with kmem_zalloc_large().

Heh.  I thought the reason why _greedy still exists (for its sole user
bulkstat) is that bulkstat had the flexibility to deal with receiving
0, 1, or 4 pages.  So yeah, we could just kill it.

But thinking even more stingily about memory, are there applications
that care about being able to bulkstat 16384 inodes at once?  How badly
does bulkstat need to be able to bulk-process more than a page's worth
of inobt records, anyway?

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

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#1592391 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

On Fri, Mar 03, 2017 at 03:19:12PM -0800, Darrick J. Wong wrote:
> On Sat, Mar 04, 2017 at 09:54:44AM +1100, Dave Chinner wrote:
> > 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>
> > > ---
> > >  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;
> > >  	}
> > 
> > Seems wrong to me - this function used to have lots of callers and
> > over time we've slowly removed them or replaced them with something
> > else. I'd suggest removing it completely, replacing the call sites
> > with kmem_zalloc_large().
> 
> Heh.  I thought the reason why _greedy still exists (for its sole user
> bulkstat) is that bulkstat had the flexibility to deal with receiving
> 0, 1, or 4 pages.  So yeah, we could just kill it.

irbuf is sized to minimise AGI locking, but if memory is low
it just uses what it can get. Keep in mind the number of inodes we
need to process is determined by the userspace buffer size, which
can easily be sized to hold tens of thousands of struct
xfs_bulkstat.

> But thinking even more stingily about memory, are there applications
> that care about being able to bulkstat 16384 inodes at once?

IIRC, xfsdump can bulkstat up to 64k inodes per call....

> How badly
> does bulkstat need to be able to bulk-process more than a page's worth
> of inobt records, anyway?

Benchmark it on a busy system doing lots of other AGI work (e.g. a
busy NFS server workload with a working set of tens of millions of
inodes so it doesn't fit in cache) and find out. That's generally
how I answer those sorts of questions...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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#1593313 — Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

On Sat 04-03-17 09:54:44, Dave Chinner wrote:
> 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>
> > ---
> >  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;
> >  	}
> 
> Seems wrong to me - this function used to have lots of callers and
> over time we've slowly removed them or replaced them with something
> else. I'd suggest removing it completely, replacing the call sites
> with kmem_zalloc_large().

I do not really care how this gets fixed. Dropping kmem_zalloc_greedy
sounds like a way to go. I am not familiar with xfs_bulkstat to do an
edicated guess which allocation size to use. So I guess I have to
postpone this to you guys if you prefer that route though.

Thanks!
-- 
Michal Hocko
SUSE Labs

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#1591410

On Thu 02-03-17 10:30:02, Brian Foster wrote:
> On Thu, Mar 02, 2017 at 04:14:11PM +0100, Michal Hocko wrote:
[...]
> > 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

the point is that vmalloc failure modes are an implementation detail
which might change in the future. The fix should be really independent
on the current implementation that is why I think the
fatal_signal_pending is just an optimization.

> 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. ;)

Done

-- 
Michal Hocko
SUSE Labs

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#1591347

On Thu, Mar 02, 2017 at 09:51:31AM -0500, Brian Foster wrote:
> 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..

I just moved the code around, but I'll take a look as well.

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#1591406

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

: 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
: 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.

> 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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#1591167

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?

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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#1591335

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?
-- 
Michal Hocko
SUSE Labs

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#1591103

On Thu, Mar 02, 2017 at 02:27:55PM +0100, Michal Hocko wrote:
> On Thu 02-03-17 08:00:09, Brian Foster wrote:
> > 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.
> 
> As Tetsuo already pointed out, vmalloc cannot really support never-fail
> semantic with the current implementation so the semantic would have
> to be implemented in kmem_zalloc_greedy and the only way to do that
> would be to loop there and this is rather nasty as you can see from the
> reported issue because the vmalloc failure might be permanent so there
> won't be any way to make a forward progress. Breaking out of the loop
> on fatal_signal_pending pending would break the non-failing sementic.
> 

Sure..

> Besides that, there doesn't really seem to be any demand for this
> semantic in the first place so why to make this more complicated than
> necessary?
> 

That may very well be the case. I'm not necessarily against this...

> 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?

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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#1591108

On Thu 02-03-17 08:00:09, Brian Foster wrote:
> 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.

As Tetsuo already pointed out, vmalloc cannot really support never-fail
semantic with the current implementation so the semantic would have
to be implemented in kmem_zalloc_greedy and the only way to do that
would be to loop there and this is rather nasty as you can see from the
reported issue because the vmalloc failure might be permanent so there
won't be any way to make a forward progress. Breaking out of the loop
on fatal_signal_pending pending would break the non-failing sementic.

Besides that, there doesn't really seem to be any demand for this
semantic in the first place so why to make this more complicated than
necessary?

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).

-- 
Michal Hocko
SUSE Labs

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#1591219 — Re: mm allocation failure and hang when running xfstests generic/269 on xfs

Brian Foster wrote:
> 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.

vmalloc() cannot support __GFP_NOFAIL. Therefore, kmem_zalloc_greedy()
cannot support !KM_MAYFAIL. We will change kmem_zalloc_greedy() not to
use vmalloc() when we need to support !KM_MAYFAIL. That won't be now.

> 
> > > 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?
> 

The kmem code looks to me a source of problems. For example,
kmem_alloc() by RESCUER workqueue threads got stuck doing GFP_NOFS allocation.
Due to __GFP_NOWARN, warn_alloc() cannot warn allocation stalls.
Due to order <= PAGE_ALLOC_COSTLY_ORDER, the
"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)"
message cannot be printed because __alloc_pages_nodemask() does not
return. And due to GFP_NOFS without __GFP_HIGH nor __GFP_NOFAIL,
memory cannot be allocated to RESCUER thread which are trying to
allocate memory for reclaiming memory; the result is silent lockup.
(I must stop here, for this is a different thread.)

----------------------------------------
[ 1095.633625] MemAlloc: xfs-data/sda1(451) flags=0x4228060 switches=45509 seq=1 gfp=0x1604240(GFP_NOFS|__GFP_NOWARN|__GFP_COMP|__GFP_NOTRACK) order=0 delay=652073
[ 1095.633626] xfs-data/sda1   R  running task    12696   451      2 0x00000000
[ 1095.633663] Workqueue: xfs-data/sda1 xfs_end_io [xfs]
[ 1095.633665] Call Trace:
[ 1095.633668]  __schedule+0x336/0xe00
[ 1095.633671]  schedule+0x3d/0x90
[ 1095.633672]  schedule_timeout+0x20d/0x510
[ 1095.633675]  ? lock_timer_base+0xa0/0xa0
[ 1095.633678]  schedule_timeout_uninterruptible+0x2a/0x30
[ 1095.633680]  __alloc_pages_slowpath+0x2b5/0xd95
[ 1095.633687]  __alloc_pages_nodemask+0x3e4/0x460
[ 1095.633699]  alloc_pages_current+0x97/0x1b0
[ 1095.633702]  new_slab+0x4cb/0x6b0
[ 1095.633706]  ___slab_alloc+0x3a3/0x620
[ 1095.633728]  ? kmem_alloc+0x96/0x120 [xfs]
[ 1095.633730]  ? ___slab_alloc+0x5c6/0x620
[ 1095.633732]  ? cpuacct_charge+0x38/0x1e0
[ 1095.633767]  ? kmem_alloc+0x96/0x120 [xfs]
[ 1095.633770]  __slab_alloc+0x46/0x7d
[ 1095.633773]  __kmalloc+0x301/0x3b0
[ 1095.633802]  kmem_alloc+0x96/0x120 [xfs]
[ 1095.633804]  ? kfree+0x1fa/0x330
[ 1095.633842]  xfs_log_commit_cil+0x489/0x710 [xfs]
[ 1095.633864]  __xfs_trans_commit+0x83/0x260 [xfs]
[ 1095.633883]  xfs_trans_commit+0x10/0x20 [xfs]
[ 1095.633901]  __xfs_setfilesize+0xdb/0x240 [xfs]
[ 1095.633936]  xfs_setfilesize_ioend+0x89/0xb0 [xfs]
[ 1095.633954]  ? xfs_setfilesize_ioend+0x5/0xb0 [xfs]
[ 1095.633971]  xfs_end_io+0x81/0x110 [xfs]
[ 1095.633973]  process_one_work+0x22b/0x760
[ 1095.633975]  ? process_one_work+0x194/0x760
[ 1095.633997]  rescuer_thread+0x1f2/0x3d0
[ 1095.634002]  kthread+0x10f/0x150
[ 1095.634003]  ? worker_thread+0x4b0/0x4b0
[ 1095.634004]  ? kthread_create_on_node+0x70/0x70
[ 1095.634007]  ret_from_fork+0x31/0x40
[ 1095.634013] MemAlloc: xfs-eofblocks/s(456) flags=0x4228860 switches=15435 seq=1 gfp=0x1400240(GFP_NOFS|__GFP_NOWARN) order=0 delay=293074
[ 1095.634014] xfs-eofblocks/s R  running task    12032   456      2 0x00000000
[ 1095.634037] Workqueue: xfs-eofblocks/sda1 xfs_eofblocks_worker [xfs]
[ 1095.634038] Call Trace:
[ 1095.634040]  ? _raw_spin_lock+0x3d/0x80
[ 1095.634042]  ? vmpressure+0xd0/0x120
[ 1095.634044]  ? vmpressure+0xd0/0x120
[ 1095.634047]  ? vmpressure_prio+0x21/0x30
[ 1095.634049]  ? do_try_to_free_pages+0x70/0x300
[ 1095.634052]  ? try_to_free_pages+0x131/0x3f0
[ 1095.634058]  ? __alloc_pages_slowpath+0x3ec/0xd95
[ 1095.634065]  ? __alloc_pages_nodemask+0x3e4/0x460
[ 1095.634069]  ? alloc_pages_current+0x97/0x1b0
[ 1095.634111]  ? xfs_buf_allocate_memory+0x160/0x2a3 [xfs]
[ 1095.634133]  ? xfs_buf_get_map+0x2be/0x480 [xfs]
[ 1095.634169]  ? xfs_buf_read_map+0x2c/0x400 [xfs]
[ 1095.634204]  ? xfs_trans_read_buf_map+0x186/0x830 [xfs]
[ 1095.634222]  ? xfs_btree_read_buf_block.constprop.34+0x78/0xc0 [xfs]
[ 1095.634239]  ? xfs_btree_lookup_get_block+0x8a/0x180 [xfs]
[ 1095.634257]  ? xfs_btree_lookup+0xd0/0x3f0 [xfs]
[ 1095.634296]  ? kmem_zone_alloc+0x96/0x120 [xfs]
[ 1095.634299]  ? _raw_spin_unlock+0x27/0x40
[ 1095.634315]  ? xfs_bmbt_lookup_eq+0x1f/0x30 [xfs]
[ 1095.634348]  ? xfs_bmap_del_extent+0x1b2/0x1610 [xfs]
[ 1095.634380]  ? kmem_zone_alloc+0x96/0x120 [xfs]
[ 1095.634400]  ? __xfs_bunmapi+0x4db/0xda0 [xfs]
[ 1095.634421]  ? xfs_bunmapi+0x2b/0x40 [xfs]
[ 1095.634459]  ? xfs_itruncate_extents+0x1df/0x780 [xfs]
[ 1095.634502]  ? xfs_rename+0xc70/0x1080 [xfs]
[ 1095.634525]  ? xfs_free_eofblocks+0x1c4/0x230 [xfs]
[ 1095.634546]  ? xfs_inode_free_eofblocks+0x18d/0x280 [xfs]
[ 1095.634565]  ? xfs_inode_ag_walk.isra.13+0x2b5/0x620 [xfs]
[ 1095.634582]  ? xfs_inode_ag_walk.isra.13+0x91/0x620 [xfs]
[ 1095.634618]  ? xfs_inode_clear_eofblocks_tag+0x1a0/0x1a0 [xfs]
[ 1095.634630]  ? radix_tree_next_chunk+0x10b/0x2d0
[ 1095.634635]  ? radix_tree_gang_lookup_tag+0xd7/0x150
[ 1095.634672]  ? xfs_perag_get_tag+0x11d/0x370 [xfs]
[ 1095.634690]  ? xfs_perag_get_tag+0x5/0x370 [xfs]
[ 1095.634709]  ? xfs_inode_ag_iterator_tag+0x71/0xa0 [xfs]
[ 1095.634726]  ? xfs_inode_clear_eofblocks_tag+0x1a0/0x1a0 [xfs]
[ 1095.634744]  ? __xfs_icache_free_eofblocks+0x3b/0x40 [xfs]
[ 1095.634759]  ? xfs_eofblocks_worker+0x27/0x40 [xfs]
[ 1095.634762]  ? process_one_work+0x22b/0x760
[ 1095.634763]  ? process_one_work+0x194/0x760
[ 1095.634784]  ? rescuer_thread+0x1f2/0x3d0
[ 1095.634788]  ? kthread+0x10f/0x150
[ 1095.634789]  ? worker_thread+0x4b0/0x4b0
[ 1095.634790]  ? kthread_create_on_node+0x70/0x70
[ 1095.634793]  ? ret_from_fork+0x31/0x40
----------------------------------------

> Brian
> 
> > -- 
> > Michal Hocko
> > SUSE Labs

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