Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control_buf access

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 28, 2024 at 03:52:26PM +0800, Heng Qi wrote:
> Refactored the handling of control_buf to be within the cvq_lock
> critical section, mitigating race conditions between reading device
> responses and new command submissions.
> 
> Fixes: 6f45ab3e0409 ("virtio_net: Add a lock for the command VQ.")
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>


I don't get what does this change. status can change immediately
after you drop the mutex, can it not? what exactly is the
race conditions you are worried about?

> ---
>  drivers/net/virtio_net.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6b0512a628e0..3d8407d9e3d2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
>  {
>  	struct scatterlist *sgs[5], hdr, stat;
>  	u32 out_num = 0, tmp, in_num = 0;
> +	bool ret;
>  	int err;
>  
>  	/* Caller should know better */
> @@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
>  	}
>  
>  unlock:
> +	ret = vi->ctrl->status == VIRTIO_NET_OK;
>  	mutex_unlock(&vi->cvq_lock);
> -	return vi->ctrl->status == VIRTIO_NET_OK;
> +	return ret;
>  }
>  
>  static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> -- 
> 2.32.0.3.g01195cf9f