On 2/24/21 8:20 AM, Chao Leng wrote:

On 2021/2/24 15:06, Hannes Reinecke wrote:

quoted

On 2/24/21 7:42 AM, Chao Leng wrote:

quoted

On 2021/2/23 20:07, Hannes Reinecke wrote:

quoted

Hi all,

one of our customer had been running into a deadlock trying to 
terminate
outstanding KATO commands during reset.
Looking closer at it, I found that we never actually _track_ if a KATO
command is submitted, so we might happily be sending several KATO 
commands
to the same controller simultaneously.

Can you explain how can send KATO commands simultaneously?

Sure.
Call nvme_start_keep_alive() on a dead connection.
Just _after_ the KATO request has been sent,
call nvme_start_keep_alive() again.

Call nvme_start_keep_alive() again? why?
Now just nvme_start_ctrl call nvme_start_keep_alive().
The ka_work will be canceled sync before start reconnection.
Did I miss something?

My point was that there _can_ be a ka_work() entry even when a KATO 
command is running.

And yes, the ka_work entry will be cancelled, but _before_ the 
outstanding commands are cancelled.
And cancelling the ka_work entry might cause the function to be 
executed, which leads to a deadlock if blk_mq_get_request() is blocked
(eg if the queue is already stopped due to recovery)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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