On Mon, 31 Jan 2022 15:33:37 -0500, David Jeffery wrote:

When blk_mq_delay_run_hw_queues sets an hctx to run in the future, it can
reset the delay length for an already pending delayed work run_work. This
creates a scenario where multiple hctx may have their queues set to run,
but if one runs first and finds nothing to do, it can reset the delay of
another hctx and stall the other hctx's ability to run requests.

To avoid this I/O stall when an hctx's run_work is already pending,
leave it untouched to run at its current designated time rather than
extending its delay. The work will still run which keeps closed the race
calling blk_mq_delay_run_hw_queues is needed for while also avoiding the
I/O stall.

[...]

Applied, thanks!

[1/1] blk-mq: avoid extending delays of active hctx from blk_mq_delay_run_hw_queues
      commit: 8f5fea65b06de1cc51d4fc23fb4d378d1abd6ed7

Best regards,
-- 
Jens Axboe