From: Jason Wang <jasowang@redhat.com>
Date: Mon, 26 Mar 2018 16:10:23 +0800
Subject: vhost_net: add missing lock nesting notation
Git-commit: aaa3149bbee9ba9b4e6f0bd6e3e7d191edeae942
Patch-mainline: v4.16
References: networking-stable-18_04_10

We try to hold TX virtqueue mutex in vhost_net_rx_peek_head_len()
after RX virtqueue mutex is held in handle_rx(). This requires an
appropriate lock nesting notation to calm down deadlock detector.

Fixes: 0308813724606 ("vhost_net: basic polling support")
Reported-by: syzbot+7f073540b1384a614e09@syzkaller.appspotmail.com
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/vhost/net.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -544,7 +544,7 @@ static int vhost_net_rx_peek_head_len(st
 
 	if (!len && vq->busyloop_timeout) {
 		/* Both tx vq and rx socket were polled here */
-		mutex_lock(&vq->mutex);
+		mutex_lock_nested(&vq->mutex, 1);
 		vhost_disable_notify(&net->dev, vq);
 
 		preempt_disable();
@@ -677,7 +677,7 @@ static void handle_rx(struct vhost_net *
 	struct iov_iter fixup;
 	__virtio16 num_buffers;
 
-	mutex_lock(&vq->mutex);
+	mutex_lock_nested(&vq->mutex, 0);
 	sock = vq->private_data;
 	if (!sock)
 		goto out;