blk-mq: call commit_rqs while list empty but error happen

Blk-mq should call commit_rqs once 'bd.last != true' and no more
request will come(so virtscsi can kick the virtqueue, e.g.). We already
do that in 'blk_mq_dispatch_rq_list/blk_mq_try_issue_list_directly' while
list not empty and 'queued > 0'. However, we can seen the same scene
once the last request in list call queue_rq and return error like
BLK_STS_IOERR which will not requeue the request, and lead that list
empty but need call commit_rqs too(Or the request for virtscsi will stay
timeout until other request kick virtqueue).

We found this problem by do fsstress test with offline/online virtscsi
device repeat quickly.

Fixes: d666ba98f849 ("blk-mq: add mq_ops->commit_rqs()")
Reported-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b3d2785..cdced4a 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1412,6 +1412,11 @@ out:
 
        hctx->dispatched[queued_to_index(queued)]++;
 
+       /* If we didn't flush the entire list, we could have told the driver
+        * there was more coming, but that turned out to be a lie.
+        */
+       if ((!list_empty(list) || errors) && q->mq_ops->commit_rqs && queued)
+               q->mq_ops->commit_rqs(hctx);
        /*
         * Any items that need requeuing? Stuff them into hctx->dispatch,
         * that is where we will continue on next queue run.
@@ -1425,14 +1430,6 @@ out:
 
                blk_mq_release_budgets(q, nr_budgets);
 
-               /*
-                * If we didn't flush the entire list, we could have told
-                * the driver there was more coming, but that turned out to
-                * be a lie.
-                */
-               if (q->mq_ops->commit_rqs && queued)
-                       q->mq_ops->commit_rqs(hctx);
-
                spin_lock(&hctx->lock);
                list_splice_tail_init(list, &hctx->dispatch);
                spin_unlock(&hctx->lock);
@@ -2079,6 +2076,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
                struct list_head *list)
 {
        int queued = 0;
+       int errors = 0;
 
        while (!list_empty(list)) {
                blk_status_t ret;
@@ -2095,6 +2093,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
                                break;
                        }
                        blk_mq_end_request(rq, ret);
+                       errors++;
                } else
                        queued++;
        }
@@ -2104,7 +2103,8 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
         * the driver there was more coming, but that turned out to
         * be a lie.
         */
-       if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs && queued)
+       if ((!list_empty(list) || errors) &&
+            hctx->queue->mq_ops->commit_rqs && queued)
                hctx->queue->mq_ops->commit_rqs(hctx);
 }