Hello James and Steve,

I will add a comment.

Please note that the above patch does not change the behavior of
nvme_stop_queues() except that it causes nvme_stop_queues() to wait
until any ongoing nvme_queue_rq() calls have finished.
blk_resume_queue() does not affect the value of the BLK_MQ_S_STOPPED bit
that has been set by blk_mq_stop_hw_queues(). All it does is to resume
pending blk_queue_enter() calls and to ensure that future
blk_queue_enter() calls do not block. Even after blk_resume_queue() has
been called if a new request is queued queue_rq() won't be invoked
because the BLK_MQ_S_STOPPED bit is still set. Patch "dm: Fix a race
condition related to stopping and starting queues" realizes a similar
change in the dm driver and that change has been tested extensively.

Thanks for the detailed explanation!  I think your code, then, is correct as-is.   And this series doesn't fix the issue I'm hitting, so I'll keep digging. :)

Steve.