[dm-devel] [PATCH 0/3] blk-mq/dm-rq: support BLK_MQ_F_BLOCKING for dm-rq

[Christoph Hellwig]

On Tue, Dec 21, 2021 at 10:14:56PM +0800, Ming Lei wrote:
> Hello,
> 
> dm-rq may be built on blk-mq device which marks BLK_MQ_F_BLOCKING, so
> dm_mq_queue_rq() may become to sleep current context.
> 
> Fixes the issue by allowing dm-rq to set BLK_MQ_F_BLOCKING in case that
> any underlying queue is marked as BLK_MQ_F_BLOCKING.
> 
> DM request queue is allocated before allocating tagset, this way is a
> bit special, so we need to pre-allocate srcu payload, then use the queue
> flag of QUEUE_FLAG_BLOCKING for locking dispatch.

What is the benefit over just forcing bio-based dm-mpath for these
devices?