[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 19:48:33
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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);
--
2.7.4