From 3c782d67c16889d753a79a8da5422c583d7cfd51 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 26 Jan 2017 12:50:36 -0700
Subject: [PATCH] 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>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Tested-by: Hannes Reinecke <hare@suse.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 1f948d5c2715b..fd80101c7591a 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);
--
2.39.5