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 <axboe@xxxxxx>
> ---
> 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@xxxxxx>
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@xxxxxx>
---
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
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