Date:	Tue, 21 Jul 2015 11:59:34 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, xfs@....sgi.com
Subject: [regression 4.2-rc3] loop: xfstests xfs/073 deadlocked in low memory
 conditions

Hi Ming,

With the recent merge of the loop device changes, I'm now seeing
XFS deadlock on my single CPU, 1GB RAM VM running xfs/073.

The deadlocked is as follows:

kloopd1: loop_queue_read_work
	xfs_file_iter_read
	lock XFS inode XFS_IOLOCK_SHARED (on image file)
	page cache read (GFP_KERNEL)
	radix tree alloc
	memory reclaim
	reclaim XFS inodes
	log force to unpin inodes
	<wait for log IO completion>

xfs-cil/loop1: <does log force IO work>
	xlog_cil_push
	xlog_write
	<loop issuing log writes>
		xlog_state_get_iclog_space()
		<blocks due to all log buffers under write io>
		<waits for IO completion>

kloopd1: loop_queue_write_work
	xfs_file_write_iter
	lock XFS inode XFS_IOLOCK_EXCL (on image file)
	<wait for inode to be unlocked>

[The full stack traces are below].

i.e. the kloopd, with it's split read and write work queues, has
introduced a dependency through memory reclaim. i.e. that writes
need to be able to progress for reads make progress.

The problem, fundamentally, is that mpage_readpages() does a
GFP_KERNEL allocation, rather than paying attention to the inode's
mapping gfp mask, which is set to GFP_NOFS.

The didn't used to happen, because the loop device used to issue
reads through the splice path and that does:

	error = add_to_page_cache_lru(page, mapping, index,
			GFP_KERNEL & mapping_gfp_mask(mapping));

i.e. it pays attention to the allocation context placed on the
inode and so is doing GFP_NOFS allocations here and avoiding the
recursion problem.

[ CC'd Michal Hocko and the mm list because it's a clear exaple of
why ignoring the mapping gfp mask on any page cache allocation is
a landmine waiting to be tripped over. ]

Cheers,

Dave.

[81248.855166] kworker/u3:0    D ffff88003a8fadc8 11304   930      2 0x00000000
[81248.855166] Workqueue: kloopd1 loop_queue_read_work
[81248.855166]  ffff88003a8fadc8 ffff880003e48000 ffff8800332fdd00 ffff88003a8fadb8
[81248.855166]  ffff88003a8fc000 ffff88003a8faf18 ffff8800332fdd00 ffff88003a8faf10
[81248.855166]  ffffffffffffffff ffff88003a8fade8 ffffffff81db608e ffff88003fc153c0
[81248.855166] Call Trace:
[81248.855166]  [<ffffffff81db608e>] schedule+0x3e/0x90
[81248.855166]  [<ffffffff81dba38f>] schedule_timeout+0x1cf/0x240
[81248.855166]  [<ffffffff810cce16>] ? try_to_wake_up+0x1f6/0x330
[81248.855166]  [<ffffffff81db7534>] wait_for_completion+0xb4/0x120
[81248.855166]  [<ffffffff810cd010>] ? wake_up_q+0x70/0x70
[81248.855166]  [<ffffffff810bc2d9>] flush_work+0xf9/0x170
[81248.855166]  [<ffffffff810ba0d0>] ? destroy_worker+0x90/0x90
[81248.855166]  [<ffffffff81513a2c>] xlog_cil_force_lsn+0xcc/0x250
[81248.855166]  [<ffffffff815126f2>] _xfs_log_force_lsn+0x82/0x2f0
[81248.855166]  [<ffffffff8151298e>] xfs_log_force_lsn+0x2e/0xa0
[81248.855166]  [<ffffffff81501e49>] ? xfs_iunpin_wait+0x19/0x20
[81248.855166]  [<ffffffff814fe686>] __xfs_iunpin_wait+0xb6/0x170
[81248.855166]  [<ffffffff810e0f90>] ? autoremove_wake_function+0x40/0x40
[81248.855166]  [<ffffffff81501e49>] xfs_iunpin_wait+0x19/0x20
[81248.855166]  [<ffffffff814f6df2>] xfs_reclaim_inode+0x72/0x350
[81248.855166]  [<ffffffff814f72e2>] xfs_reclaim_inodes_ag+0x212/0x350
[81248.855166]  [<ffffffff81dbb07e>] ? _raw_spin_unlock+0xe/0x20
[81248.855166]  [<ffffffff81dbb07e>] ? _raw_spin_unlock+0xe/0x20
[81248.855166]  [<ffffffff814f74b3>] xfs_reclaim_inodes_nr+0x33/0x40
[81248.855166]  [<ffffffff81507f19>] xfs_fs_free_cached_objects+0x19/0x20
[81248.855166]  [<ffffffff811cf791>] super_cache_scan+0x191/0x1a0
[81248.855166]  [<ffffffff811912d4>] shrink_slab.part.62.constprop.80+0x1b4/0x380
[81248.855166]  [<ffffffff81194720>] shrink_zone+0x90/0xa0
[81248.855166]  [<ffffffff811948b0>] do_try_to_free_pages+0x180/0x2c0
[81248.855166]  [<ffffffff81194aaa>] try_to_free_pages+0xba/0x160
[81248.855166]  [<ffffffff81189509>] __alloc_pages_nodemask+0x499/0x840
[81248.855166]  [<ffffffff811c3d2f>] new_slab+0x6f/0x2c0
[81248.855166]  [<ffffffff811c5baa>] __slab_alloc.constprop.75+0x3fa/0x580
[81248.855166]  [<ffffffff817be438>] ? __radix_tree_preload+0x48/0xc0
[81248.855166]  [<ffffffff817be438>] ? __radix_tree_preload+0x48/0xc0
[81248.855166]  [<ffffffff811c620e>] kmem_cache_alloc+0x12e/0x160
[81248.855166]  [<ffffffff817be438>] __radix_tree_preload+0x48/0xc0
[81248.855166]  [<ffffffff817be519>] radix_tree_maybe_preload+0x19/0x20
[81248.855166]  [<ffffffff81181b69>] __add_to_page_cache_locked+0x39/0x1f0
[81248.855166]  [<ffffffff81181d68>] add_to_page_cache_lru+0x28/0x80
[81248.855166]  [<ffffffff81209fc9>] mpage_readpages+0xb9/0x130
[81248.855166]  [<ffffffff814e68e0>] ? __xfs_get_blocks+0x840/0x840
[81248.855166]  [<ffffffff814e68e0>] ? __xfs_get_blocks+0x840/0x840
[81248.855166]  [<ffffffff814e409d>] xfs_vm_readpages+0x1d/0x20
[81248.855166]  [<ffffffff8118cfc9>] __do_page_cache_readahead+0x1b9/0x250
[81248.855166]  [<ffffffff8118d13f>] ondemand_readahead+0xdf/0x270
[81248.855166]  [<ffffffff81180fc6>] ? find_get_entry+0x66/0xb0
[81248.855166]  [<ffffffff8118d362>] page_cache_async_readahead+0x92/0xc0
[81248.855166]  [<ffffffff81182c3c>] generic_file_read_iter+0x41c/0x650
[81248.855166]  [<ffffffff81db9664>] ? down_read+0x24/0x40
[81248.855166]  [<ffffffff814f1d66>] xfs_file_read_iter+0xe6/0x2d0
[81248.855166]  [<ffffffff811cba22>] vfs_iter_read+0x62/0xa0
[81248.855166]  [<ffffffff81a98fcd>] loop_handle_cmd.isra.28+0x6dd/0xaa0
[81248.855166]  [<ffffffff810cce16>] ? try_to_wake_up+0x1f6/0x330
[81248.855166]  [<ffffffff81a99472>] loop_queue_read_work+0x12/0x20
[81248.855166]  [<ffffffff810bd02e>] process_one_work+0x14e/0x410
[81248.855166]  [<ffffffff810bd63e>] worker_thread+0x4e/0x460
[81248.855166]  [<ffffffff810bd5f0>] ? rescuer_thread+0x300/0x300
[81248.855166]  [<ffffffff810c288c>] kthread+0xec/0x110
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0
[81248.855166]  [<ffffffff81dbba5f>] ret_from_fork+0x3f/0x70
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0

[81248.855166] kworker/0:0     D ffff88002ed8bb88 13896   948      2 0x00000000
[81248.855166] Workqueue: xfs-cil/loop1 xlog_cil_push_work
[81248.855166]  ffff88002ed8bb88 ffffffff82368540 ffff880003e4be00 ffff88001a467cf0
[81248.855166]  ffff88002ed8c000 ffff880005123cf8 ffff88001a467cf0 ffff880003e4be00
[81248.855166]  ffff880005123cc0 ffff88002ed8bba8 ffffffff81db608e ffff88002ed8bba8
[81248.855166] Call Trace:
[81248.855166]  [<ffffffff81db608e>] schedule+0x3e/0x90
[81248.855166]  [<ffffffff81511266>] xlog_state_get_iclog_space+0xe6/0x330
[81248.855166]  [<ffffffff810cd010>] ? wake_up_q+0x70/0x70
[81248.855166]  [<ffffffff81511666>] xlog_write+0x1b6/0x870
[81248.855166]  [<ffffffff8151316d>] xlog_cil_push+0x24d/0x400
[81248.855166]  [<ffffffff81513335>] xlog_cil_push_work+0x15/0x20
[81248.855166]  [<ffffffff810bd02e>] process_one_work+0x14e/0x410
[81248.855166]  [<ffffffff810bd63e>] worker_thread+0x4e/0x460
[81248.855166]  [<ffffffff810bd5f0>] ? rescuer_thread+0x300/0x300
[81248.855166]  [<ffffffff810bd5f0>] ? rescuer_thread+0x300/0x300
[81248.855166]  [<ffffffff810c288c>] kthread+0xec/0x110
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0
[81248.855166]  [<ffffffff81dbba5f>] ret_from_fork+0x3f/0x70
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0

[81248.855166] kworker/u3:4    D ffff8800290439f8 12456  1066      2 0x00000000
[81248.855166] Workqueue: kloopd1 loop_queue_write_work
[81248.855166]  ffff8800290439f8 ffffffff82368540 ffff8800332f9f00 ffff8800290439e8
[81248.855166]  ffff880029044000 ffffffff00000000 ffff88001366cfd8 ffffffff00000002
[81248.855166]  ffff8800332f9f00 ffff880029043a18 ffffffff81db608e ffff880029043a18
[81248.855166] Call Trace:
[81248.855166]  [<ffffffff81db608e>] schedule+0x3e/0x90
[81248.855166]  [<ffffffff81db9f3d>] rwsem_down_write_failed+0x13d/0x340
[81248.855166]  [<ffffffff810cce16>] ? try_to_wake_up+0x1f6/0x330
[81248.855166]  [<ffffffff814f2e46>] ? xfs_file_buffered_aio_write+0x66/0x250
[81248.855166]  [<ffffffff817c76a3>] call_rwsem_down_write_failed+0x13/0x20
[81248.855166]  [<ffffffff81db96bf>] ? down_write+0x3f/0x60
[81248.855166]  [<ffffffff814fdea4>] xfs_ilock+0x154/0x1d0
[81248.855166]  [<ffffffff814f2e46>] xfs_file_buffered_aio_write+0x66/0x250
[81248.855166]  [<ffffffff8179264d>] ? kblockd_schedule_work+0x1d/0x30
[81248.855166]  [<ffffffff8179dbc5>] ? blk_mq_kick_requeue_list+0x15/0x20
[81248.855166]  [<ffffffff814f3136>] xfs_file_write_iter+0x106/0x120
[81248.855166]  [<ffffffff811cbac3>] vfs_iter_write+0x63/0xa0
[81248.855166]  [<ffffffff81a97828>] lo_write_bvec+0x58/0x100
[81248.855166]  [<ffffffff81a99248>] loop_handle_cmd.isra.28+0x958/0xaa0
[81248.855166]  [<ffffffff81a9941f>] loop_queue_write_work+0x8f/0xd0
[81248.855166]  [<ffffffff810bd02e>] process_one_work+0x14e/0x410
[81248.855166]  [<ffffffff810bd63e>] worker_thread+0x4e/0x460
[81248.855166]  [<ffffffff810bd5f0>] ? rescuer_thread+0x300/0x300
[81248.855166]  [<ffffffff810c288c>] kthread+0xec/0x110
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0
[81248.855166]  [<ffffffff81dbba5f>] ret_from_fork+0x3f/0x70
[81248.855166]  [<ffffffff810c27a0>] ? kthread_create_on_node+0x1b0/0x1b0
-- 
Dave Chinner
david@...morbit.com
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