linux-ext4 - v4.19-rc2: ext4 direct I/O recursive locking complaint

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Date:   Sun, 09 Sep 2018 14:53:29 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     linux-ext4@...r.kernel.org
Subject: v4.19-rc2: ext4 direct I/O recursive locking complaint

Hello,

While running blktests against kernel v4.19-rc2 the circular locking
complaint shown belown appeared. I never saw this complaint for any previous
kernel version, including v4.18. Could this be an ext4 regression?

Thanks,

Bart.

======================================================
WARNING: possible circular locking dependency detected
4.19.0-rc2-dbg+ #1 Not tainted
------------------------------------------------------
kworker/1:2/189 is trying to acquire lock:
00000000fcf597b9 (&sb->s_type->i_mutex_key#16){+.+.}, at:
__generic_file_fsync+0x6a/0xf0

but task is already holding lock:
000000008a4b0074 ((work_completion)(&dio->complete_work)){+.+.}, at:
process_one_work+0x3f6/0xa70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((work_completion)(&dio->complete_work)){+.+.}:
       worker_thread+0x65/0x5a0
       kthread+0x1c5/0x1f0
       ret_from_fork+0x24/0x30

-> #1 ((wq_completion)"dio/%s"sb->s_id){+.+.}:
       drain_workqueue+0xe5/0x210
       destroy_workqueue+0x1c/0x320
       sb_init_dio_done_wq+0x65/0x80
       do_blockdev_direct_IO+0x3b8/0x3d00
       ext4_direct_IO+0x5d9/0xbd0
       generic_file_direct_write+0x10f/0x210
       __generic_file_write_iter+0x117/0x2a0
       ext4_file_write_iter+0x394/0x670
       aio_write+0x235/0x330
       io_submit_one+0x510/0xeb0
       __x64_sys_io_submit+0x122/0x340
       do_syscall_64+0x6c/0x210
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sb->s_type->i_mutex_key#16){+.+.}:
       down_write+0x39/0x70
       __generic_file_fsync+0x6a/0xf0
       ext4_sync_file+0x3c4/0x770
       dio_complete+0x2f6/0x360
       process_one_work+0x4bc/0xa70
       worker_thread+0x65/0x5a0
       kthread+0x1c5/0x1f0
       ret_from_fork+0x24/0x30

other info that might help us debug this:

Chain exists of:
  &sb->s_type->i_mutex_key#16 --> (wq_completion)"dio/%s"sb->s_id -->
(work_completion)(&dio->complete_work)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&dio->complete_work));
                               lock((wq_completion)"dio/%s"sb->s_id);
                               lock((work_completion)(&dio->complete_work));
  lock(&sb->s_type->i_mutex_key#16);

 *** DEADLOCK ***

2 locks held by kworker/1:2/189:
 #0: 00000000ae279ea2 ((wq_completion)"dio/%s"sb->s_id){+.+.}, at:
process_one_work+0x3f6/0xa70
 #1: 000000008a4b0074 ((work_completion)(&dio->complete_work)){+.+.}, at:
process_one_work+0x3f6/0xa70

stack backtrace:
CPU: 1 PID: 189 Comm: kworker/1:2 Not tainted 4.19.0-rc2-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1
04/01/2014
Workqueue: dio/dm-0 dio_aio_complete_work
Call Trace:
 dump_stack+0x7c/0xbb
 print_circular_bug.isra.32+0x1fc/0x209
 __lock_acquire+0x1a54/0x1b20
 lock_acquire+0xbd/0x200
 down_write+0x39/0x70
 __generic_file_fsync+0x6a/0xf0
 ext4_sync_file+0x3c4/0x770
 dio_complete+0x2f6/0x360
 process_one_work+0x4bc/0xa70
 worker_thread+0x65/0x5a0
 kthread+0x1c5/0x1f0
 ret_from_fork+0x24/0x30