[PATCH 08/12] dm: Fix a race condition related to stopping and starting queues

[Mike Snitzer]

On Wed, Oct 26 2016 at  6:54pm -0400,
Bart Van Assche <bart.vanassche at sandisk.com> wrote:

> Ensure that all ongoing dm_mq_queue_rq() and dm_mq_requeue_request()
> calls have stopped before setting the "queue stopped" flag. This
> allows to remove the "queue stopped" test from dm_mq_queue_rq() and
> dm_mq_requeue_request(). This patch fixes a race condition because
> dm_mq_queue_rq() is called without holding the queue lock and hence
> BLK_MQ_S_STOPPED can be set at any time while dm_mq_queue_rq() is
> in progress. This patch prevents that the following hang occurs
> sporadically when using dm-mq:
> 
> INFO: task systemd-udevd:10111 blocked for more than 480 seconds.
> Call Trace:
>  [<ffffffff8161f397>] schedule+0x37/0x90
>  [<ffffffff816239ef>] schedule_timeout+0x27f/0x470
>  [<ffffffff8161e76f>] io_schedule_timeout+0x9f/0x110
>  [<ffffffff8161fb36>] bit_wait_io+0x16/0x60
>  [<ffffffff8161f929>] __wait_on_bit_lock+0x49/0xa0
>  [<ffffffff8114fe69>] __lock_page+0xb9/0xc0
>  [<ffffffff81165d90>] truncate_inode_pages_range+0x3e0/0x760
>  [<ffffffff81166120>] truncate_inode_pages+0x10/0x20
>  [<ffffffff81212a20>] kill_bdev+0x30/0x40
>  [<ffffffff81213d41>] __blkdev_put+0x71/0x360
>  [<ffffffff81214079>] blkdev_put+0x49/0x170
>  [<ffffffff812141c0>] blkdev_close+0x20/0x30
>  [<ffffffff811d48e8>] __fput+0xe8/0x1f0
>  [<ffffffff811d4a29>] ____fput+0x9/0x10
>  [<ffffffff810842d3>] task_work_run+0x83/0xb0
>  [<ffffffff8106606e>] do_exit+0x3ee/0xc40
>  [<ffffffff8106694b>] do_group_exit+0x4b/0xc0
>  [<ffffffff81073d9a>] get_signal+0x2ca/0x940
>  [<ffffffff8101bf43>] do_signal+0x23/0x660
>  [<ffffffff810022b3>] exit_to_usermode_loop+0x73/0xb0
>  [<ffffffff81002cb0>] syscall_return_slowpath+0xb0/0xc0
>  [<ffffffff81624e33>] entry_SYSCALL_64_fastpath+0xa6/0xa8
> 
> Signed-off-by: Bart Van Assche <bart.vanassche at sandisk.com>
> Reviewed-by: Hannes Reinecke <hare at suse.com>
> Reviewed-by: Johannes Thumshirn <jthumshirn at suse.de>
> Reviewed-by: Christoph Hellwig <hch at lst.de>
> Cc: Mike Snitzer <snitzer at redhat.com>

Acked-by: Mike Snitzer <snitzer at redhat.com>