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Date: Thu, 07 May 2020 17:30:04 -0700 (PDT) From: David Miller <davem@...emloft.net> To: zenczykowski@...il.com Cc: maze@...gle.com, netdev@...r.kernel.org, edumazet@...gle.com, willemb@...gle.com, lucien.xin@...il.com, hannes@...essinduktion.org Subject: Re: [PATCH] Revert "ipv6: add mtu lock check in __ip6_rt_update_pmtu" From: Maciej Żenczykowski <zenczykowski@...il.com> Date: Tue, 5 May 2020 11:57:23 -0700 > From: Maciej Żenczykowski <maze@...gle.com> > > This reverts commit 19bda36c4299ce3d7e5bce10bebe01764a655a6d: > > | ipv6: add mtu lock check in __ip6_rt_update_pmtu > | > | Prior to this patch, ipv6 didn't do mtu lock check in ip6_update_pmtu. > | It leaded to that mtu lock doesn't really work when receiving the pkt > | of ICMPV6_PKT_TOOBIG. > | > | This patch is to add mtu lock check in __ip6_rt_update_pmtu just as ipv4 > | did in __ip_rt_update_pmtu. > > The above reasoning is incorrect. IPv6 *requires* icmp based pmtu to work. > There's already a comment to this effect elsewhere in the kernel: > > $ git grep -p -B1 -A3 'RTAX_MTU lock' > net/ipv6/route.c=4813= > > static int rt6_mtu_change_route(struct fib6_info *f6i, void *p_arg) > ... > /* In IPv6 pmtu discovery is not optional, > so that RTAX_MTU lock cannot disable it. > We still use this lock to block changes > caused by addrconf/ndisc. > */ > > This reverts to the pre-4.9 behaviour. > > Signed-off-by: Maciej Żenczykowski <maze@...gle.com> > Fixes: 19bda36c4299 ("ipv6: add mtu lock check in __ip6_rt_update_pmtu") I've thought about this some more and decided to apply this and queue it up for -stable, thank you.
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