netdev - Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control

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Message-ID: <20240528114547-mutt-send-email-mst@kernel.org>
Date: Tue, 28 May 2024 11:46:28 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jiri Pirko <jiri@...nulli.us>, Daniel Jurgens <danielj@...dia.com>
Subject: Re: [PATCH net 2/2] virtio_net: fix missing lock protection on
 control_buf access

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@...ux.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