Re: [RFC PATCH] blk-mq: Clean up references when freeing rqs

[John Garry]

On 09/12/2020 01:01, Ming Lei wrote:
> blk_mq_queue_tag_busy_iter() can be run on another request queue just
> between one driver tag is allocated and updating the request map, so one
> extra request reference still can be grabbed.
>
> So looks only holding one queue's usage_counter doesn't help this issue, since
> bt_for_each() always iterates on driver tags wide.
>
> > But I didn't see such a guard for blk_mq_tagset_busy_iter().
> IMO there isn't real difference between the two iteration.

ok, I see. Let me try to recreate that one, which will prob again 
require artificial delays added.

Apart from this, my concern is that we come with for a solution, but 
it's a complicated solution and may not be accepted as this issue is not 
seen as a problem in practice.

Thanks,
John