-bouncing mail. That wasn't clever. Apologies. This one is for 4.9. Giuliano. On Mon, 8 Jun 2020 at 11:56, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Jun 08, 2020 at 10:40:30AM +0100, Giuliano Procida wrote: > > From: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx> > > > > commit f5bbbbe4d63577026f908a809f22f5fd5a90ea1f upstream. > > > > For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to > > account the inflight requests. It will access the queue_hw_ctx and > > nr_hw_queues w/o any protection. When updating nr_hw_queues and > > blk_mq_in_flight/rw occur concurrently, panic comes up. > > > > Before update nr_hw_queues, the q will be frozen. So we could use > > q_usage_counter to avoid the race. percpu_ref_is_zero is used here > > so that we will not miss any in-flight request. The access to > > nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are > > under rcu critical section, __blk_mq_update_nr_hw_queues could use > > synchronize_rcu to ensure the zeroed q_usage_counter to be globally > > visible. > > > > Backporting Notes > > > > This is a re-backport, landing synchronize_rcu in the right place. > > You sent this twice? > > And what stable kernel(s) does it go to? > > thanks, > > greg k-h
