[PATCH 4.15 167/168] vhost_net: add missing lock nesting notation

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasow...@redhat.com>


[ Upstream commit aaa3149bbee9ba9b4e6f0bd6e3e7d191edeae942 ]

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+7f073540b1384a614...@syzkaller.appspotmail.com
Signed-off-by: Jason Wang <jasow...@redhat.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/vhost/net.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -618,7 +618,7 @@ 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();
@@ -751,7 +751,7 @@ 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;