netdev - Re: [PATCH net 1/2] tun: handle ubuf refcount correctly when meet erros

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Date:   Wed, 30 Nov 2016 15:57:48 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        wangyunjian@...wei.com
Subject: Re: [PATCH net 1/2] tun: handle ubuf refcount correctly when meet
 erros

On Wed, Nov 30, 2016 at 01:17:51PM +0800, Jason Wang wrote:
> We trigger uarg->callback() immediately after we decide do datacopy
> even if caller want to do zerocopy. This will cause the callback
> (vhost_net_zerocopy_callback) decrease the refcount. But when we meet
> an error afterwards, the error handling in vhost handle_tx() will try
> to decrease it again. This is wrong and fix this by delay the
> uarg->callback() until we're sure there's no errors.
> 
> Reported-by: wangyunjian <wangyunjian@...wei.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

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

> ---
> The patch is needed for -stable.
> ---
>  drivers/net/tun.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 8093e39..db6acec 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1246,13 +1246,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  
>  	if (zerocopy)
>  		err = zerocopy_sg_from_iter(skb, from);
> -	else {
> +	else
>  		err = skb_copy_datagram_from_iter(skb, 0, from, len);
> -		if (!err && msg_control) {
> -			struct ubuf_info *uarg = msg_control;
> -			uarg->callback(uarg, false);
> -		}
> -	}
>  
>  	if (err) {
>  		this_cpu_inc(tun->pcpu_stats->rx_dropped);
> @@ -1298,6 +1293,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  		skb_shinfo(skb)->destructor_arg = msg_control;
>  		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
>  		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
> +	} else if (msg_control) {
> +		struct ubuf_info *uarg = msg_control;
> +		uarg->callback(uarg, false);
>  	}
>  
>  	skb_reset_network_header(skb);
> -- 
> 2.7.4