On Thu, Apr 15, 2021 at 06:33:10PM +0800, Ming Lei wrote: > For bio based request queue, the queue usage refcnt is only grabbed > during submission, which isn't consistent with request base queue. > > Queue freezing has been used widely, and turns out it is very useful > to quiesce queue activity. > > Support to freeze bio based request queue by the following approach: > > 1) grab two queue usage refcount for blk-mq before submitting blk-mq > bio, one is for bio, anther is for request; > > 2) add bio flag of BIO_QUEUE_REFFED for making sure that only one > refcnt is grabbed for each bio, so we can put the refcnt when the > bio is going away > > 3) nvme mpath is a bit special, because same bio is used for both > mpath queue and underlying nvme queue. So we put the mpath queue's > usage refcnt before completing the nvme request. RAID needs similar handling too, but it is easy to do, see md_end_io(). -- Ming
