RE: [PATCH] block-mq: set both block queue and hardware queue restart bit for restart

Long Li
2017-04-06T03:38:37Z

> From: Bart Van Assche [mailto:Bart.VanAssche@sandisk.com]
> Sent: Wednesday, April 5, 2017 5:32 PM
> To: linux-kernel@vger.kernel.org; linux-block@vger.kernel.org; Long Li
> <longli@microsoft.com>; axboe@kernel.dk
> Cc: Stephen Hemminger <sthemmin@microsoft.com>; KY Srinivasan
> <kys@microsoft.com>; Long Li <longli@microsoft.com>
> Subject: Re: [PATCH] block-mq: set both block queue and hardware queue
> restart bit for restart
>
> On Wed, 2017-04-05 at 17:16 -0700, Long Li wrote:
> > Under heavy I/O, one hardware queue may be unable to dispatch any I/O
> > to the device layer. This poses a problem with restarting this
> > hardware queue on I/O finish in blk_mq_sched_restart_queues(), becaue
> > there is nothing pending that will finish in future on this hardware qeueu.
> This will result in deadlock.
> >
> > With this patch, we check for all possible stalled hardware queues
> > when I/O finishes on any hardware queues. This prevents this deadlock.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> > block/blk-mq-sched.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index
> > 09af8ff..f7f3d44 100644
> > --- a/block/blk-mq-sched.c
> > +++ b/block/blk-mq-sched.c
> > @@ -202,7 +202,7 @@ void blk_mq_sched_dispatch_requests(struct
> blk_mq_hw_ctx *hctx)
> > * needing a restart in that case.
> > */
> > if (!list_empty(&rq_list)) {
> > - blk_mq_sched_mark_restart_hctx(hctx);
> > + blk_mq_sched_mark_restart_queue(hctx);
> > did_work = blk_mq_dispatch_rq_list(hctx, &rq_list);
> > } else if (!has_sched_dispatch) {
> > blk_mq_flush_busy_ctxs(hctx, &rq_list);
>
> Please drop this patch. I'm working on a better solution.

Thank you. Looking forward to your patch.

>
> Thanks,
>
> Bart.