netdev - Re: [PATCH net] ipv4: lock mtu in fnhe when received PMTU < net.ipv4.route.min

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Message-Id: <20180309.160619.741646019216536916.davem@davemloft.net>
Date:   Fri, 09 Mar 2018 16:06:19 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, sbrivio@...hat.com
Subject: Re: [PATCH net] ipv4: lock mtu in fnhe when received PMTU <
 net.ipv4.route.min_pmtu

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Fri,  9 Mar 2018 17:43:21 +0100

> diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
> index f80524396c06..77d0a78cf7d2 100644
> --- a/include/net/ip_fib.h
> +++ b/include/net/ip_fib.h
> @@ -59,6 +59,7 @@ struct fib_nh_exception {
>  	int				fnhe_genid;
>  	__be32				fnhe_daddr;
>  	u32				fnhe_pmtu;
> +	bool				fnhe_mtu_locked;
>  	__be32				fnhe_gw;
>  	unsigned long			fnhe_expires;
>  	struct rtable __rcu		*fnhe_rth_input;
> diff --git a/include/net/route.h b/include/net/route.h
> index 1eb9ce470e25..729bb5e61e9a 100644
> --- a/include/net/route.h
> +++ b/include/net/route.h
> @@ -64,6 +64,7 @@ struct rtable {
>  
>  	/* Miscellaneous cached information */
>  	u32			rt_pmtu;
> +	bool			rt_mtu_locked;
>  
>  	u32			rt_table_id;
>  

Please use a flag bit for this, we've worked hard to shrink these
datastructures as much as possible.

I think if you just choose an unused RTCF_* bit (f.e. 0x02000000) for
the state, you can use that because values propagate into the
rtable->rt_flags, and do not propagate out.  So you should be able to
use it in this way privately inside the kernel.

Thanks.