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

[David Miller]

From: Sabrina Dubroca 
Date: Mon, 12 Mar 2018 17:05:28 +0100

> 2018-03-09, 16:06:19 -0500, David Miller wrote:
>> From: Sabrina Dubroca 
>> Date: Fri,  9 Mar 2018 17:43:21 +0100
>> 
>> I think if you just choose an unused RTCF_* bit (f.e. 0x0200) 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.
> 
> What about a bitfield?
> 
> - u32 rt_pmtu;
> + u32 rt_mtu_locked:1,
> + rt_pmtu:31;

I guess that's fine.

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

[Sabrina Dubroca]

2018-03-09, 16:06:19 -0500, David Miller wrote:
> From: Sabrina Dubroca 
> 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;
> > +   boolfnhe_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;
> > +   boolrt_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.

Oops, sorry.

> I think if you just choose an unused RTCF_* bit (f.e. 0x0200) 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.

What about a bitfield?

-   u32 rt_pmtu;
+   u32 rt_mtu_locked:1,
+   rt_pmtu:31;

Since it's going to be private to the kernel, I'd rather not use a
value that's in uapi, especially considering that they're almost all
used (unless we start recycling).

-- 
Sabrina

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

[David Miller]

From: Sabrina Dubroca 
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;
> + boolfnhe_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;
> + boolrt_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. 0x0200) 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.