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_run_work > and run_work) > > > 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_rq() 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.
