netdev - Re: [PATCH net] vhost_net: add missing lock nesting notation

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Date:   Mon, 26 Mar 2018 16:24:20 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] vhost_net: add missing lock nesting notation

On Mon, Mar 26, 2018 at 04:10:23PM +0800, Jason Wang wrote:
> 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@...kaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/vhost/net.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 8139bc7..12bcfba 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -630,7 +630,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
>  
>  	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();
> @@ -763,7 +763,7 @@ static void handle_rx(struct vhost_net *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;
> -- 
> 2.7.4