On Mon, 2018-01-29 at 16:44 -0500, Mike Snitzer wrote: > But regardless of which wins the race, the queue will have been run. > Which is all we care about right? Running the queue is not sufficient. With this patch applied it can happen that the block driver returns BLK_STS_DEV_RESOURCE, that the two or more concurrent queue runs finish before sufficient device resources are available to execute the request and that blk_mq_delay_run_hw_queue() does not get called at all. If no other activity triggers a queue run, e.g. request completion, this will result in a queue stall. Bart.
