Re: [PATCH] blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter

[Greg KH <gregkh@linuxfoundation.org>]

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