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

Bart Van Assche
2017-04-06T00:32:28Z

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.

Thanks,

Bart.