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

[David Miller]

From: Sabrina Dubroca <s...@queasysnail.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.