Re: [PATCH 2/5] blk-mq: fix potential race in queue restart and driver tag allocation
From: Jens Axboe <axboe@fb.com>
Date: 2017-01-26 19:52:15
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
On 01/26/2017 12:48 PM, Jens Axboe wrote:
quoted hunk ↗ jump to hunk
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 <axboe@fb.com> --- 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 <axboe@fb.com> 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 <axboe@fb.com> --- 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