[PATCH] virtio_blk: Fix signedness bug in virtblk_prep_rq()

[Rafael Mendonca <rafaelmendsr@gmail.com>]

The virtblk_map_data() function returns negative error codes, however, the
'nents' field of vbr->sg_table is an unsigned int, which causes the error
handling not to work correctly.

Fixes: 0e9911fa768f ("virtio-blk: support mq_ops->queue_rqs()")
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
---
 drivers/block/virtio_blk.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 19da5defd734..291f705e61a8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -321,16 +321,18 @@ static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
 					struct virtblk_req *vbr)
 {
 	blk_status_t status;
+	int num;
 
 	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
 	if (unlikely(status))
 		return status;
 
-	vbr->sg_table.nents = virtblk_map_data(hctx, req, vbr);
-	if (unlikely(vbr->sg_table.nents < 0)) {
+	num = virtblk_map_data(hctx, req, vbr);
+	if (unlikely(num < 0)) {
 		virtblk_cleanup_cmd(req);
 		return BLK_STS_RESOURCE;
 	}
+	vbr->sg_table.nents = num;
 
 	blk_mq_start_request(req);
 
-- 
2.34.1