[dm-devel] [PATCH 1/5] blk-mq: introduce BLK_STS_DEV_RESOURCE

[Bart Van Assche]

On Wed, 2018-01-24 at 00:59 +0800, Ming Lei wrote:
> How is that enough to fix the IO hang when driver returns STS_RESOURCE
> and the queue is idle? If you want to follow previous dm-rq's way of
> call blk_mq_delay_run_hw_queue() in .queue_rq(), the same trick need
> to be applied to other drivers too, right?
> 
> Unfortunately most of STS_RESOURCE don't use this trick, but they need
> to be handled.
> 
> The patch of 'blk-mq: introduce BLK_STS_DEV_RESOURCE' can fix all these
> cases.

The goal of my proposal was to address the race between running the queue and
adding requests back to the dispatch queue only. Regarding the I/O hangs that
can occur if a block driver returns BLK_STS_RESOURCE: since all of these can
be addressed by inserting blk_mq_delay_run_hw_queue() calls in the affected
block drivers I prefer to modify the block drivers instead of making the
blk-mq core even more complicated.

Thanks,

Bart.