Re: [PATCH 0/4] blk-mq: support to use hw tag for scheduling

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Thu, 2017-05-04 at 00:52 +0800, Ming Lei wrote:
> Looks v4.11 plus your for-linus often triggers the following hang during
> boot, and it seems caused by the change in (blk-mq: unify hctx delayed_ru=
n_work
> and run_work)
>=20
>=20
> BUG: scheduling while atomic: kworker/0:1H/704/0x00000002
> Modules linked in:
> Preemption disabled at:
> [<ffffffffaf5607bb>] virtio_queue_rq+0xdb/0x350
> CPU: 0 PID: 704 Comm: kworker/0:1H Not tainted 4.11.0-04508-ga1f35f46164b=
 #132
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.9.3-1.fc25 04/=
01/2014
> Workqueue: kblockd blk_mq_run_work_fn
> Call Trace:
>  dump_stack+0x65/0x8f
>  ? virtio_queue_rq+0xdb/0x350
>  __schedule_bug+0x76/0xc0
>  __schedule+0x610/0x820
>  ? new_slab+0x2c9/0x590
>  schedule+0x40/0x90
>  schedule_timeout+0x273/0x320
>  ? ___slab_alloc+0x3cb/0x4f0
>  wait_for_completion+0x97/0x100
>  ? wait_for_completion+0x97/0x100
>  ? wake_up_q+0x80/0x80
>  flush_work+0x104/0x1a0
>  ? flush_workqueue_prep_pwqs+0x130/0x130
>  __cancel_work_timer+0xeb/0x160
>  ? vp_notify+0x16/0x20
>  ? virtqueue_add_sgs+0x23c/0x4a0
>  cancel_delayed_work_sync+0x13/0x20
>  blk_mq_stop_hw_queue+0x16/0x20
>  virtio_queue_rq+0x316/0x350
>  blk_mq_dispatch_rq_list+0x194/0x350
>  blk_mq_sched_dispatch_requests+0x118/0x170
>  ? finish_task_switch+0x80/0x1e0
>  __blk_mq_run_hw_queue+0xa3/0xc0
>  blk_mq_run_work_fn+0x2c/0x30
>  process_one_work+0x1e0/0x400
>  worker_thread+0x48/0x3f0
>  kthread+0x109/0x140
>  ? process_one_work+0x400/0x400
>  ? kthread_create_on_node+0x40/0x40
>  ret_from_fork+0x2c/0x40

Callers of blk_mq_quiesce_queue() really need blk_mq_stop_hw_queue() to
cancel delayed work synchronously. The above call stack shows that we have
to do something about the blk_mq_stop_hw_queue() calls from inside .queue_r=
q()
functions for queues for which BLK_MQ_F_BLOCKING has not been set. I'm not
sure what the best approach would be: setting BLK_MQ_F_BLOCKING for queues
that call blk_mq_stop_hw_queue() from inside .queue_rq() or creating two
versions of blk_mq_stop_hw_queue().

Bart.=