Subject: Re: [PATCH v4 3/5] vsock/virtio: fix locking in virtio_transport_inc_tx_pkt()

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 17 Jul 2019 10:51:47 -0400

On Wed, Jul 17, 2019 at 01:30:28PM +0200, Stefano Garzarella wrote:
> fwd_cnt and last_fwd_cnt are protected by rx_lock, so we should use
> the same spinlock also if we are in the TX path.
> 
> Move also buf_alloc under the same lock.
> 
> Signed-off-by: Stefano Garzarella <[email-masked]>

Wait a second is this a bugfix?
If it's used under the wrong lock won't values get corrupted?
Won't traffic then stall or more data get to sent than
credits?

> ---
>  include/linux/virtio_vsock.h            | 2 +-
>  net/vmw_vsock/virtio_transport_common.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 49fc9d20bc43..4c7781f4b29b 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -35,7 +35,6 @@ struct virtio_vsock_sock {
>  
>  	/* Protected by tx_lock */
>  	u32 tx_cnt;
> -	u32 buf_alloc;
>  	u32 peer_fwd_cnt;
>  	u32 peer_buf_alloc;
>  
> @@ -43,6 +42,7 @@ struct virtio_vsock_sock {
>  	u32 fwd_cnt;
>  	u32 last_fwd_cnt;
>  	u32 rx_bytes;
> +	u32 buf_alloc;
>  	struct list_head rx_queue;
>  };
>  
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index a85559d4d974..34a2b42313b7 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -210,11 +210,11 @@ static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
>  
>  void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
>  {
> -	spin_lock_bh(&vvs->tx_lock);
> +	spin_lock_bh(&vvs->rx_lock);
>  	vvs->last_fwd_cnt = vvs->fwd_cnt;
>  	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
>  	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
> -	spin_unlock_bh(&vvs->tx_lock);
> +	spin_unlock_bh(&vvs->rx_lock);
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);
>  
> -- 
> 2.20.1