Re: [PATCH V3 1/1] blk-mq: avoid double ->queue_rq() because of early timeout

[Ming Lei <ming.lei@redhat.com>]

On Wed, Oct 26, 2022 at 01:19:57PM +0800, Ming Lei wrote:
> From: David Jeffery <djeffery@redhat.com>
> 
> David Jeffery found one double ->queue_rq() issue, so far it can
> be triggered in VM use case because of long vmexit latency or preempt
> latency of vCPU pthread or long page fault in vCPU pthread, then block
> IO req could be timed out before queuing the request to hardware but after
> calling blk_mq_start_request() during ->queue_rq(), then timeout handler
> may handle it by requeue, then double ->queue_rq() is caused, and kernel
> panic.
> 
> So far, it is driver's responsibility to cover the race between timeout
> and completion, so it seems supposed to be solved in driver in theory,
> given driver has enough knowledge.
> 
> But it is really one common problem, lots of driver could have similar
> issue, and could be hard to fix all affected drivers, even it isn't easy
> for driver to handle the race. So David suggests this patch by draining
> in-progress ->queue_rq() for solving this issue.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Keith Busch <kbusch@kernel.org>
> Cc: virtualization@lists.linux-foundation.org
> Cc: Bart Van Assche <bvanassche@acm.org>
> Signed-off-by: David Jeffery <djeffery@redhat.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> V3:
> 	- add callback for handle expired only, suggested by Keith Busch

Hi Jens,

Any chance to merge this fix? Either 6.1 or 6.2 is fine for me.


Thanks,
Ming