Re: [PATCH 1/2] blk-mq: introduce blk_mq_complete_request_sync()

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On 3/17/19 8:29 PM, Ming Lei wrote:
In NVMe's error handler, follows the typical steps for tearing down
hardware:

1) stop blk_mq hw queues
2) stop the real hw queues
3) cancel in-flight requests via
	blk_mq_tagset_busy_iter(tags, cancel_request, ...)
cancel_request():
	mark the request as abort
	blk_mq_complete_request(req);
4) destroy real hw queues

However, there may be race between #3 and #4, because blk_mq_complete_request()
actually completes the request asynchronously.

This patch introduces blk_mq_complete_request_sync() for fixing the
above race.

Other block drivers wait until outstanding requests have completed by calling blk_cleanup_queue() before hardware queues are destroyed. Why can't the NVMe driver follow that approach?

Thanks,

Bart.



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