Re: [Xen-devel] [PATCH] xen-blkfront: fix mq start/stop race

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jul 19, 2017 at 09:19:49AM +0800, Junxiao Bi wrote:
> Hi Roger,
> 
> On 06/23/2017 08:57 PM, Roger Pau Monné wrote:
> > On Thu, Jun 22, 2017 at 09:36:52AM +0800, Junxiao Bi wrote:
> >> When ring buf full, hw queue will be stopped. While blkif interrupt consume
> >> request and make free space in ring buf, hw queue will be started again.
> >> But since start queue is protected by spin lock while stop not, that will
> >> cause a race.
> >>
> >> interrupt:                                      process:
> >> blkif_interrupt()                               blkif_queue_rq()
> >>  kick_pending_request_queues_locked()
> >>   blk_mq_start_stopped_hw_queues()
> >>    clear_bit(BLK_MQ_S_STOPPED, &hctx->state)
> >>                                                  blk_mq_stop_hw_queue(hctx)
> >>    blk_mq_run_hw_queue(hctx, async)
> >>
> >> If ring buf is made empty in this case, interrupt will never come, then the
> >> hw queue will be stopped forever, all processes waiting for the pending io
> >> in the queue will hung.
> >>
> >> Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> >> Reviewed-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> > 
> > Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Looks patch not in mainline. Can you please help merge it?

I'm afraid this needs to be done by Konrad or one of the Linux
maintainers, I don't have an account on kernel.org in order to send
pull requests to Jens.

Roger.

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