netdev - Re: [PATCH 1/2] net/ipv6: always honour route mtu during forwarding

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Date:   Thu, 8 Oct 2020 09:31:11 -0700
From:   David Ahern <dsahern@...il.com>
To:     Maciej Żenczykowski <zenczykowski@...il.com>,
        Maciej Żenczykowski <maze@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        Sunmeet Gill <sgill@...cinc.com>,
        Vinay Paradkar <vparadka@....qualcomm.com>,
        Tyler Wear <twear@...cinc.com>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH 1/2] net/ipv6: always honour route mtu during forwarding

On 10/7/20 8:31 PM, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <maze@...gle.com>
> 
> This matches the new ipv4 behaviour as of commit:
>   commit 02a1b175b0e92d9e0fa5df3957ade8d733ceb6a0
>   Author: Maciej Żenczykowski <maze@...gle.com>
>   Date:   Wed Sep 23 13:18:15 2020 -0700
> 
>   net/ipv4: always honour route mtu during forwarding

just summarize that as:
commit 02a1b175b0e9 ("net/ipv4: always honour route mtu during forwarding")



> diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
> index 2a5277758379..598415743f46 100644
> --- a/include/net/ip6_route.h
> +++ b/include/net/ip6_route.h
> @@ -311,19 +311,13 @@ static inline bool rt6_duplicate_nexthop(struct fib6_info *a, struct fib6_info *
>  static inline unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
>  {
>  	struct inet6_dev *idev;
> -	unsigned int mtu;
> +	unsigned int mtu = dst_metric_raw(dst, RTAX_MTU);

newline here for readability

> +	if (mtu)
> +		return mtu;
>  
> -	if (dst_metric_locked(dst, RTAX_MTU)) {
> -		mtu = dst_metric_raw(dst, RTAX_MTU);
> -		if (mtu)
> -			return mtu;
> -	}
> -
> -	mtu = IPV6_MIN_MTU;
>  	rcu_read_lock();
>  	idev = __in6_dev_get(dst->dev);
> -	if (idev)
> -		mtu = idev->cnf.mtu6;
> +	mtu = idev ? idev->cnf.mtu6 : IPV6_MIN_MTU;
>  	rcu_read_unlock();
>  
>  	return mtu;
> 

besides the nit comments, the change looks fine to me. Please add test
cases to tools/testing/selftests/net/pmtu.sh for this change.