Re: [PATCH] block: don't call blk_mq_run_hw_queues() for dead or dying queues

Hannes Reinecke
2019-03-26T14:08:16Z

On 3/26/19 2:43 PM, Bart Van Assche wrote:
> On 3/26/19 5:07 AM, Hannes Reinecke wrote:
>> When a queue is dying or dead there is no point in calling
>> blk_mq_run_hw_queues() in blk_mq_unquiesce_queue(); in fact, doing
>> so might crash the machine as the queue structures are in the
>> process of being deleted.
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.com>
>> ---
>>   block/blk-mq.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index a9c181603cbd..b1eeba38bc79 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -258,7 +258,8 @@ void blk_mq_unquiesce_queue(struct request_queue *q)
>>       blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
>>       /* dispatch requests which are inserted during quiescing */
>> -    blk_mq_run_hw_queues(q, true);
>> +    if (!blk_queue_dying(q) && !blk_queue_dead(q))
>> +        blk_mq_run_hw_queues(q, true);
>>   }
>>   EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
>
> Hi Hannes,
>
> Please provide more context information. In the "dead" state the queue
> must be run to make sure that all requests that were queued before the
> "dead" state get processed. The blk_cleanup_queue() function is
> responsible for stopping all code that can run the queue after all
> requests have finished and before destruction of the data structures
> needed for request processing starts.
>
I have a crash with two processes competing for the same controller:

#0 0xffffffff983d3bcb in sbitmap_any_bit_set (sb=0xffff8a1b874ba0d8)
at ../lib/sbitmap.c:181
#1 0xffffffff98366c05 in blk_mq_hctx_has_pending (hctx=0xffff8a1b874ba000)
at ../block/blk-mq.c:66
#2 0xffffffff98366c85 in blk_mq_run_hw_queues (q=0xffff8a1b874ba0d8,
async=true) at ../block/blk-mq.c:1292
#3 0xffffffff98366d3a in blk_mq_unquiesce_queue (q=<optimized out>)
at ../block/blk-mq.c:265
#4 0xffffffffc01f3e0e in nvme_start_queues (ctrl=<optimized out>)
at ../drivers/nvme/host/core.c:3658
#5 0xffffffffc01e843c in nvme_fc_delete_association
(ctrl=0xffff8a1f9be5a000)
at ../drivers/nvme/host/fc.c:2843
#6 0xffffffffc01e8544 in nvme_fc_delete_association (ctrl=<optimized out>)
at ../drivers/nvme/host/fc.c:2918
#7 0xffffffffc01e8544 in __nvme_fc_terminate_io (ctrl=0xffff8a1f9be5a000)
at ../drivers/nvme/host/fc.c:2911
#8 0xffffffffc01e8f09 in nvme_fc_reset_ctrl_work (work=0xffff8a1f9be5a6d0)
at ../drivers/nvme/host/fc.c:2927
#9 0xffffffff980a224a in process_one_work (worker=0xffff8a1b73934f00,
work=0xffff8a1f9be5a6d0) at ../kernel/workqueue.c:2092
#10 0xffffffff980a249b in worker_thread (__worker=0xffff8a1b73934f00)
at ../kernel/workqueue.c:2226

#7 0xffffffff986d2e9a in wait_for_completion (x=0xffffa48eca88bc40)
at ../kernel/sched/completion.c:125
#8 0xffffffff980f25ae in __synchronize_srcu (sp=0xffffffff9914fc20
<debugfs_srcu>, do_norm=<optimized out>) at ../kernel/rcu/srcutree.c:851
#9 0xffffffff982d18b1 in debugfs_remove_recursive (dentry=<optimized out>)
at ../fs/debugfs/inode.c:741
#10 0xffffffff98398ac5 in blk_mq_debugfs_unregister_hctx
(hctx=0xffff8a1b7cccc000) at ../block/blk-mq-debugfs.c:897
#11 0xffffffff983661cf in blk_mq_exit_hctx (q=0xffff8a1f825e4040,
set=0xffff8a1f9be5a0c0, hctx=0xffff8a1b7cccc000, hctx_idx=2) at
../block/blk-mq.c:1987
#12 0xffffffff9836946a in blk_mq_exit_hw_queues (nr_queue=<optimized
out>, set=<optimized out>, q=<optimized out>) at ../block/blk-mq.c:2017
#13 0xffffffff9836946a in blk_mq_free_queue (q=0xffff8a1f825e4040)
at ../block/blk-mq.c:2506
#14 0xffffffff9835aac5 in blk_cleanup_queue (q=0xffff8a1f825e4040)
at ../block/blk-core.c:691
#15 0xffffffffc01f5bc8 in nvme_ns_remove (ns=0xffff8a1f819e8f80)
at ../drivers/nvme/host/core.c:3138
#16 0xffffffffc01f6fea in nvme_validate_ns (ctrl=0xffff8a1f9be5a308, nsid=5)
at ../drivers/nvme/host/core.c:3164
#17 0xffffffffc01f9053 in nvme_scan_ns_list (nn=<optimized out>,
ctrl=<optimized out>) at ../drivers/nvme/host/core.c:3202
#18 0xffffffffc01f9053 in nvme_scan_work (work=<optimized out>)
at ../drivers/nvme/host/core.c:3280
#19 0xffffffff980a224a in process_one_work (worker=0xffff8a1b7349f6c0,
work=0xffff8a1f9be5aba0) at ../kernel/workqueue.c:2092

Point is that the queue is already dead by the time nvme_start_queues()
tries to flush existing requests (of which there are none, of course).
I had been looking into synchronizing scan_work and reset_work, but then
I wasn't sure if that wouldn't deadlock somewhere.

Cheers,

Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@suse.de +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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