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

From: Yafang Shao <laoar.shao@gmail.com>
To: darrick.wong@oracle.com
Cc: linux-xfs@vger.kernel.org, Yafang Shao <laoar.shao@gmail.com>
Subject: [RFC PATCH] xfs: avoid deadlock when tigger memory reclam in xfs_map_blocks()
Date: Wed,  3 Jun 2020 06:10:35 -0400	[thread overview]
Message-ID: <1591179035-9270-1-git-send-email-laoar.shao@gmail.com> (raw)

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]
[480594.790314]  [<ffffffff8118d881>] write_cache_pages+0x251/0x4d0 [xfs]
[480594.790338]  [<ffffffffa04d3e05>] xfs_vm_writepages+0xc5/0xe0 [xfs]
[480594.790341]  [<ffffffff8118ebfe>] do_writepages+0x1e/0x40
[480594.790343]  [<ffffffff811837b5>] __filemap_fdatawrite_range+0x65/0x80
[480594.790346]  [<ffffffff81183901>] filemap_write_and_wait_range+0x41/0x90
[480594.790360]  [<ffffffffa04df2c6>] xfs_file_fsync+0x66/0x1e0 [xfs]
[480594.790363]  [<ffffffff81231cf5>] do_fsync+0x65/0xa0
[480594.790365]  [<ffffffff81231fe3>] SyS_fdatasync+0x13/0x20
[480594.790367]  [<ffffffff81698d09>] system_call_fastpath+0x16/0x1b

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 fs/xfs/xfs_aops.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 1fd4fb7..3f60766 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -352,6 +352,7 @@ static inline bool xfs_ioend_needs_workqueue(struct iomap_ioend *ioend)
 	struct xfs_iext_cursor	icur;
 	int			retries = 0;
 	int			error = 0;
+	unsigned int		nofs_flag;
 
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -EIO;
@@ -445,8 +446,16 @@ static inline bool xfs_ioend_needs_workqueue(struct iomap_ioend *ioend)
 	xfs_bmbt_to_iomap(ip, &wpc->iomap, &imap, 0);
 	trace_xfs_map_blocks_found(ip, offset, count, whichfork, &imap);
 	return 0;
+
 allocate_blocks:
+	/*
+	 * We can allocate memory here while doing writeback on behalf of
+	 * memory reclaim.  To avoid memory allocation deadlocks set the
+	 * task-wide nofs context for the following operations.
+	 */
+	nofs_flag = memalloc_nofs_save();
 	error = xfs_convert_blocks(wpc, ip, whichfork, offset);
+	memalloc_nofs_restore(nofs_flag);
 	if (error) {
 		/*
 		 * If we failed to find the extent in the COW fork we might have
-- 
1.8.3.1

