-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@linuxfoundation.org wrote:
On Mon, Jun 08, 2020 at 10:40:30AM +0100, Giuliano Procida wrote:
From: Jianchao Wang jianchao.w.wang@oracle.com
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