linux-kernel - Re: [PATCH net-next] tun/macvtap: use consume_skb() instead of kfree_skb() in tun/macvtap_do

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Message-ID: <1416983160.29427.52.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 25 Nov 2014 22:26:00 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com
Subject: Re: [PATCH net-next] tun/macvtap: use consume_skb() instead of
 kfree_skb() in tun/macvtap_do_read()

On Wed, 2014-11-26 at 14:08 +0800, Jason Wang wrote:
> To be more friendly with drop monitor, we should use comsume_skb() instead
> of kfree_skb() in tun/macvtap_do_read(). Otherwise, the packets will be
> marked as dropped.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/macvtap.c | 2 +-
>  drivers/net/tun.c     | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 42a80d3..74d1b23 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -862,7 +862,7 @@ static ssize_t macvtap_do_read(struct macvtap_queue *q,
>  		}
>  		iov_iter_init(&iter, READ, iv, segs, len);
>  		ret = macvtap_put_user(q, skb, &iter);
> -		kfree_skb(skb);
> +		consume_skb(skb);
>  		break;
>  	}
>  
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index ac53a73..d7edeaf 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1363,7 +1363,7 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
>  
>  	iov_iter_init(&iter, READ, iv, segs, len);
>  	ret = tun_put_user(tun, tfile, skb, &iter);
> -	kfree_skb(skb);
> +	consume_skb(skb);
>  
>  	return ret;
>  }


These patches keep going on, but they are wrong.

If you care about drop monitor, then you want to not hide drops but
precisely report them.

Surely tun_put_user() can return an error, and then packet _is_ dropped.



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