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Message-ID: <11723218.PRMC7IWbep@minako> Date: Thu, 30 Aug 2018 23:49:08 +0200 From: Jan Janssen <medhefgo@....de> To: dsahern@...nel.org Cc: netdev@...r.kernel.org, David Ahern <dsahern@...il.com> Subject: Re: [PATCH net] net/ipv6: Only update MTU metric if it set On Donnerstag, 30. August 2018 23:15:43 CEST dsahern@...nel.org wrote: > From: David Ahern <dsahern@...il.com> > > Jan reported a regression after an update to 4.18.5. In this case ipv6 > default route is setup by systemd-networkd based on data from an RA. The > RA contains an MTU of 1492 which is used when the route is first inserted > but then systemd-networkd pushes down updates to the default route > without the mtu set. > > Prior to the change to fib6_info, metrics such as MTU were held in the > dst_entry and rt6i_pmtu in rt6_info contained an update to the mtu if > any. ip6_mtu would look at rt6i_pmtu first and use it if set. If not, > the value from the metrics is used if it is set and finally falling > back to the idev value. > > After the fib6_info change metrics are contained in the fib6_info struct > and there is no equivalent to rt6i_pmtu. To maintain consistency with > the old behavior the new code should only reset the MTU in the metrics > if the route update has it set. > > Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info") > Reported-by: Jan Janssen <medhefgo@....de> > Signed-off-by: David Ahern <dsahern@...il.com> > --- > net/ipv6/ip6_fib.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c > index d212738e9d10..f43d278e0040 100644 > --- a/net/ipv6/ip6_fib.c > +++ b/net/ipv6/ip6_fib.c > @@ -987,7 +987,10 @@ static int fib6_add_rt2node(struct fib6_node *fn, > struct fib6_info *rt, fib6_clean_expires(iter); > else > fib6_set_expires(iter, rt->expires); > - fib6_metric_set(iter, RTAX_MTU, rt->fib6_pmtu); > + > + if (rt->fib6_pmtu) > + fib6_metric_set(iter, RTAX_MTU, > + rt->fib6_pmtu); > return -EEXIST; > } > /* If we have the same destination and the same metric, I just tested this and can confirm that it fixes my problem. You mentioned that systemd-networkd is doing something silly here, so I was wondering if you could make a bug report to fix the underlying issue? I don't mind doing it myself but you're the expert and can explain things better. Thank you for fixing this.
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