When copy_to_iter() fails in vduse_dev_read_iter(), put the message back
at the head of send_list to preserve FIFO ordering and retry the oldest
pending request first.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
Reported-by: Michael S. Tsirkin <mst@redhat.com>
Suggested-by: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Zhang Tianci <zhangtianci.1997@bytedance.com>
Reviewed-by: Xie Yongji <xieyongji@bytedance.com>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index ae357d014564c..b37f18a0ce6fd 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -194,6 +194,12 @@ static void vduse_enqueue_msg(struct list_head *head,
 	list_add_tail(&msg->list, head);
 }
 
+static void vduse_enqueue_msg_head(struct list_head *head,
+				   struct vduse_dev_msg *msg)
+{
+	list_add(&msg->list, head);
+}
+
 static void vduse_dev_broken(struct vduse_dev *dev)
 {
 	struct vduse_dev_msg *msg, *tmp;
@@ -354,7 +360,7 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	spin_lock(&dev->msg_lock);
 	if (ret != size) {
 		ret = -EFAULT;
-		vduse_enqueue_msg(&dev->send_list, msg);
+		vduse_enqueue_msg_head(&dev->send_list, msg);
 		goto unlock;
 	}
 	vduse_enqueue_msg(&dev->recv_list, msg);
-- 
2.39.5