Re: [RFC PATCH] xfs: avoid deadlock when tigger memory reclam in xfs_map_blocks()

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Jun 4, 2020 at 6:27 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Wed, Jun 03, 2020 at 10:23:55AM -0700, Darrick J. Wong wrote:
> > On Wed, Jun 03, 2020 at 06:10:35AM -0400, Yafang Shao wrote:
> > > Recently there is an XFS deadlock on our server with an old kernel.
> > > The deadlock is caused by allocating memory xfs_map_blocks() while doing
> > > writeback on behalf of memroy reclaim. Although this deadlock happens on an
> > > old kernel, I think it could happen on the newest kernel as well. This
> > > issue only happence once and can't be reproduced, so I haven't tried to
> > > produce it on the newesr kernel.
> > >
> > > Bellow is the call trace of this deadlock. Note that
> > > xfs_iomap_write_allocate() is replaced by xfs_convert_blocks() in
> > > commit 4ad765edb02a ("xfs: move xfs_iomap_write_allocate to xfs_aops.c").
> > >
> > > [480594.790087] INFO: task redis-server:16212 blocked for more than 120 seconds.
> > > [480594.790087] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [480594.790088] redis-server    D ffffffff8168bd60     0 16212  14347 0x00000004
> > > [480594.790090]  ffff880da128f070 0000000000000082 ffff880f94a2eeb0 ffff880da128ffd8
> > > [480594.790092]  ffff880da128ffd8 ffff880da128ffd8 ffff880f94a2eeb0 ffff88103f9d6c40
> > > [480594.790094]  0000000000000000 7fffffffffffffff ffff88207ffc0ee8 ffffffff8168bd60
> > > [480594.790096] Call Trace:
> > > [480594.790101]  [<ffffffff8168dce9>] schedule+0x29/0x70
> > > [480594.790103]  [<ffffffff8168b749>] schedule_timeout+0x239/0x2c0
> > > [480594.790111]  [<ffffffff8168d28e>] io_schedule_timeout+0xae/0x130
> > > [480594.790114]  [<ffffffff8168d328>] io_schedule+0x18/0x20
> > > [480594.790116]  [<ffffffff8168bd71>] bit_wait_io+0x11/0x50
> > > [480594.790118]  [<ffffffff8168b895>] __wait_on_bit+0x65/0x90
> > > [480594.790121]  [<ffffffff811814e1>] wait_on_page_bit+0x81/0xa0
> > > [480594.790125]  [<ffffffff81196ad2>] shrink_page_list+0x6d2/0xaf0
> > > [480594.790130]  [<ffffffff811975a3>] shrink_inactive_list+0x223/0x710
> > > [480594.790135]  [<ffffffff81198225>] shrink_lruvec+0x3b5/0x810
> > > [480594.790139]  [<ffffffff8119873a>] shrink_zone+0xba/0x1e0
> > > [480594.790141]  [<ffffffff81198c20>] do_try_to_free_pages+0x100/0x510
> > > [480594.790143]  [<ffffffff8119928d>] try_to_free_mem_cgroup_pages+0xdd/0x170
> > > [480594.790145]  [<ffffffff811f32de>] mem_cgroup_reclaim+0x4e/0x120
> > > [480594.790147]  [<ffffffff811f37cc>] __mem_cgroup_try_charge+0x41c/0x670
> > > [480594.790153]  [<ffffffff811f5cb6>] __memcg_kmem_newpage_charge+0xf6/0x180
> > > [480594.790157]  [<ffffffff8118c72d>] __alloc_pages_nodemask+0x22d/0x420
> > > [480594.790162]  [<ffffffff811d0c7a>] alloc_pages_current+0xaa/0x170
> > > [480594.790165]  [<ffffffff811db8fc>] new_slab+0x30c/0x320
> > > [480594.790168]  [<ffffffff811dd17c>] ___slab_alloc+0x3ac/0x4f0
> > > [480594.790204]  [<ffffffff81685656>] __slab_alloc+0x40/0x5c
> > > [480594.790206]  [<ffffffff811dfc43>] kmem_cache_alloc+0x193/0x1e0
> > > [480594.790233]  [<ffffffffa04fab67>] kmem_zone_alloc+0x97/0x130 [xfs]
> > > [480594.790247]  [<ffffffffa04f90ba>] _xfs_trans_alloc+0x3a/0xa0 [xfs]
> > > [480594.790261]  [<ffffffffa04f915c>] xfs_trans_alloc+0x3c/0x50 [xfs]
> > > [480594.790276]  [<ffffffffa04e958b>] xfs_iomap_write_allocate+0x1cb/0x390 [xfs]
> > > [480594.790299]  [<ffffffffa04d3616>] xfs_map_blocks+0x1a6/0x210 [xfs]
> > > [480594.790312]  [<ffffffffa04d416b>] xfs_do_writepage+0x17b/0x550 [xfs]
> >
> > xfs_do_writepages doesn't exist anymore.  Does upstream have this
> > problem?  What kernel is this patch targeting?
>
> It does via xfs_bmapi_convert_delalloc() -> xfs_trans_alloc().
>
> I suspect the entire iomap_do_writepage() path should be run under
> GFP_NOFS context given that it is called with a locked page
> cache page and calls ->map_blocks from that context...
>

Agreed, I will send v2.



-- 
Thanks
Yafang