diff options
authorShaohua Li <shli@fb.com>2015-05-04 14:32:48 -0600
committerJens Axboe <axboe@fb.com>2015-05-04 14:32:48 -0600
commit9ba52e5812e53f20f23600d79449a3ec05a0254f (patch)
parentb2387ddcced8de3e6471a2fb16a409577063016f (diff)
blk-mq: don't lose requests if a stopped queue restarts
Normally if driver is busy to dispatch a request the logic is like below: block layer: driver: __blk_mq_run_hw_queue a. blk_mq_stop_hw_queue b. rq add to ctx->dispatch later: 1. blk_mq_start_hw_queue 2. __blk_mq_run_hw_queue But it's possible step 1-2 runs between a and b. And since rq isn't in ctx->dispatch yet, step 2 will not run rq. The rq might get lost if there are no subsequent requests kick in. Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
1 files changed, 10 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 76f460e36f1d..e68b71b85a7e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -858,6 +858,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
list_splice(&rq_list, &hctx->dispatch);
+ /*
+ * the queue is expected stopped with BLK_MQ_RQ_QUEUE_BUSY, but
+ * it's possible the queue is stopped and restarted again
+ * before this. Queue restart will dispatch requests. And since
+ * requests in rq_list aren't added into hctx->dispatch yet,
+ * the requests in rq_list might get lost.
+ *
+ * blk_mq_run_hw_queue() already checks the STOPPED bit
+ **/
+ blk_mq_run_hw_queue(hctx, true);