On 01/26/2017 12:48 PM, Jens Axboe wrote: > Once we mark the queue as needing a restart, re-check if we can > get a driver tag. This fixes a theoretical issue where the needed > IO completes _after_ blk_mq_get_driver_tag() fails, but before we > manage to set the restart bit. > > Signed-off-by: Jens Axboe <[email protected]> > --- > block/blk-mq.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 223b9b080820..8041ad330289 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -928,7 +928,16 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, > struct list_head *list) > if (!blk_mq_get_driver_tag(rq, &hctx, false)) { > if (!queued && reorder_tags_to_front(list)) > continue; > + > + /* > + * We failed getting a driver tag. Mark the queue(s) > + * as needing a restart. Retry getting a tag again, > + * in case the needed IO completed right before we > + * marked the queue as needing a restart. > + */ > blk_mq_sched_mark_restart(hctx); > + if (!blk_mq_get_driver_tag(rq, &hctx, false)) > + break; > break; > } > list_del_init(&rq->queuelist);
I screwed this up when splitting up the patchset, that last break needs to be removed as well, of course. Updated below: >From 9d68cf9232c06a793e305d10b6d655df4beae928 Mon Sep 17 00:00:00 2001 From: Jens Axboe <[email protected]> Date: Thu, 26 Jan 2017 12:50:36 -0700 Subject: [PATCH 1/4] blk-mq: fix potential race in queue restart and driver tag allocation Once we mark the queue as needing a restart, re-check if we can get a driver tag. This fixes a theoretical issue where the needed IO completes _after_ blk_mq_get_driver_tag() fails, but before we manage to set the restart bit. Signed-off-by: Jens Axboe <[email protected]> --- block/blk-mq.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 223b9b080820..5cf013d87c2e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -928,8 +928,16 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list) if (!blk_mq_get_driver_tag(rq, &hctx, false)) { if (!queued && reorder_tags_to_front(list)) continue; + + /* + * We failed getting a driver tag. Mark the queue(s) + * as needing a restart. Retry getting a tag again, + * in case the needed IO completed right before we + * marked the queue as needing a restart. + */ blk_mq_sched_mark_restart(hctx); - break; + if (!blk_mq_get_driver_tag(rq, &hctx, false)) + break; } list_del_init(&rq->queuelist); -- 2.7.4 -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
