Hello Ming,

Can you have a look at the attached patch? That patch uses an srcu read
lock for all queue types, whether or not the BLK_MQ_F_BLOCKING flag has
been set. Additionally, I have dropped the QUEUE_FLAG_QUIESCING flag.
Just like previous versions, this patch has been tested.

Hey Bart,

Do we care about the synchronization of queue_rq and/or
blk_mq_run_hw_queue of the hctx is not stopped?

I'm wandering if we can avoid introducing new barriers in the
submission path of its not absolutely needed.