blk-mq: call blk_mq_start_request from ->queue_rq

When we call blk_mq_start_request from the core blk-mq code before calling into
->queue_rq there is a racy window where the timeout handler can hit before we've
fully set up the driver specific part of the command.

Move the call to blk_mq_start_request into the driver so the driver can start
the request only once it is fully set up.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 13756e016797..83816bf6882f 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -205,6 +205,8 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req,
                 }
         }
 
+        blk_mq_start_request(req);
+
         num = blk_rq_map_sg(hctx->queue, vbr->req, vbr->sg);
         if (num) {
                 if (rq_data_dir(vbr->req) == WRITE)