[PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[Stefano Brivio]

Commit 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6
tunnels") introduced a check to avoid updating PMTU when
collect_md mode is enabled.

Later, commit f15ca723c1eb ("net: don't call update_pmtu
unconditionally") dropped this check, I guess inadvertently.
Restore it.

Fixes: f15ca723c1eb ("net: don't call update_pmtu unconditionally")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 net/ipv6/ip6_tunnel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index a0b6932c3afd..6f05e0f74bdf 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1136,7 +1136,8 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 	mtu = max(mtu, skb->protocol == htons(ETH_P_IPV6) ?
 		       IPV6_MIN_MTU : IPV4_MIN_MTU);
 
-	skb_dst_update_pmtu(skb, mtu);
+	if (!t->parms.collect_md)
+		skb_dst_update_pmtu(skb, mtu);
 	if (skb->len - t->tun_hlen - eth_hlen > mtu && !skb_is_gso(skb)) {
 		*pmtu = mtu;
 		err = -EMSGSIZE;
-- 
2.19.1

Re: [PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[Nicolas Dichtel]

Le 12/10/2018 à 14:32, Stefano Brivio a écrit :
> Commit 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6
> tunnels") introduced a check to avoid updating PMTU when
> collect_md mode is enabled.
> 
> Later, commit f15ca723c1eb ("net: don't call update_pmtu
> unconditionally") dropped this check, I guess inadvertently.
I removed it because update_pmtu() is not set for md_dst_op, thus I assume this
check was done for that purpose.

Could you explain in your commit log which problem your patch fixes?

Re: [PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[Stefano Brivio]

On Fri, 12 Oct 2018 17:58:55 +0200
Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:

> Le 12/10/2018 à 14:32, Stefano Brivio a écrit :
> > Commit 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6
> > tunnels") introduced a check to avoid updating PMTU when
> > collect_md mode is enabled.
> > 
> > Later, commit f15ca723c1eb ("net: don't call update_pmtu
> > unconditionally") dropped this check, I guess inadvertently.  
> I removed it because update_pmtu() is not set for md_dst_op, thus I assume this
> check was done for that purpose.

Ha, sounds reasonable, yes.

> Could you explain in your commit log which problem your patch fixes?

Nothing really.

The change in f15ca723c1eb looked accidental and I thought it doesn't
make sense to update the PMTU in that case, but I didn't figure out
it's not actually done anyway.

Maybe it makes things a bit more readable, in that case I'd target it
for net-next. What do you think?

-- 
Stefano

Re: [PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[Nicolas Dichtel]

Le 12/10/2018 à 18:34, Stefano Brivio a écrit :
> On Fri, 12 Oct 2018 17:58:55 +0200
> Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:
[snip]
>> Could you explain in your commit log which problem your patch fixes?
> 
> Nothing really.
> 
> The change in f15ca723c1eb looked accidental and I thought it doesn't
> make sense to update the PMTU in that case, but I didn't figure out
> it's not actually done anyway.
> 
> Maybe it makes things a bit more readable, in that case I'd target it
> for net-next. What do you think?
> 
I don't think that this patch helps. The purpose of the skb_dst_update_pmtu()
helper is to hide those things. If one day, update_pmtu is defined for
md_dst_op, I bet that we won't remove this test.


Regards,
Nicolas

Re: [PATCH net] ip6_tunnel: Don't update PMTU on tunnels with collect_md

[Stefano Brivio]

On Mon, 15 Oct 2018 10:48:05 +0200
Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:

> Le 12/10/2018 à 18:34, Stefano Brivio a écrit :
> > On Fri, 12 Oct 2018 17:58:55 +0200
> > Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:  
> [snip]
> >> Could you explain in your commit log which problem your patch fixes?  
> > 
> > Nothing really.
> > 
> > The change in f15ca723c1eb looked accidental and I thought it doesn't
> > make sense to update the PMTU in that case, but I didn't figure out
> > it's not actually done anyway.
> > 
> > Maybe it makes things a bit more readable, in that case I'd target it
> > for net-next. What do you think?
> >   
> I don't think that this patch helps. The purpose of the skb_dst_update_pmtu()
> helper is to hide those things. If one day, update_pmtu is defined for
> md_dst_op, I bet that we won't remove this test.

I see, makes sense.

David, please drop this patch, and sorry for the noise.

-- 
Stefano