netdev - Re: [PATCHv2] ipv4: Do not cache routing failures due to disabled forwarding.

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Date:	Thu, 18 Sep 2014 08:17:08 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Nicolas Cavallari <nicolas.cavallari@...en-communications.fr>
cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCHv2] ipv4: Do not cache routing failures due to disabled
 forwarding.


	Hello,

On Mon, 15 Sep 2014, Nicolas Cavallari wrote:

> If we cache them, the kernel will reuse them, independently of
> whether forwarding is enabled or not.  Which means that if forwarding is
> disabled on the input interface where the first routing request comes
> from, then that unreachable result will be cached and reused for
> other interfaces, even if forwarding is enabled on them.
> 
> This can be verified with two interfaces A and B and an output interface
> C, where B has forwarding enabled, but not A and trying
> ip route get $dst iif A from $src && ip route get $dst iif B from $src
> 
> Signed-off-by: Nicolas Cavallari <nicolas.cavallari@...en-communications.fr>

	Looks good to me,

Reviewed-by: Julian Anastasov <ja@....bg>

	Still, I fail to see how the compiler optimizes
the jump, 'goto local_input' still jumps to res.fi check.
I tried even likely() after 'local_input:" checks for
res.fi and !itag but the 'if (res.fi) {' block is still
moved below and reached with jnz. I expected likely() to
prefer the res.fi != NULL path.

> ---
> v2: simplify patch using julian anastasov's suggestion.
> 
>  net/ipv4/route.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 234a43e..b09fda8 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1798,6 +1798,7 @@ local_input:
>  no_route:
>  	RT_CACHE_STAT_INC(in_no_route);
>  	res.type = RTN_UNREACHABLE;
> +	res.fi = NULL;
>  	goto local_input;
>  
>  	/*
> -- 
> 2.1.0

Regards

--
Julian Anastasov <ja@....bg>
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