linux-kernel - Re: [PATCH] block-mq: set both block queue and hardware queue restart bit for restart

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Date:   Thu, 6 Apr 2017 00:32:16 +0000
From:   Bart Van Assche <Bart.VanAssche@...disk.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "longli@...hange.microsoft.com" <longli@...hange.microsoft.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "longli@...rosoft.com" <longli@...rosoft.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@...rosoft.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.

Thanks,

Bart.