On Wed, 2016-03-16 at 22:38 -0400, David Miller wrote: > From: Eric Dumazet <eric.duma...@gmail.com> > Date: Wed, 16 Mar 2016 17:22:07 -0700 > > > One of the issue is that IPV6_MTU getsockopt() will not check the dst, > > but simply use __sk_dst_get() : It will then report old mtu. > > That's a bug. > > ipv4 does it right with a proper sk_dst_get() and so should > ipv6.
Using rcu + __sk_dst_get() (in IPv6) is absolutely equivalent to sk_dst_get() + dst_release() (in IPv4), modulo atomic ops on dst refcnt... Presumably IPv6 implementation using rcu is slightly better if this getsockopt() is badly needed, but apparently nobody cares. sk_dst_check() is a different beast. The problem is that dst_mtu(dst) is not able to perform a route lookup by itself. Do we really want to use ip6_sk_dst_lookup_flow() and its associated setup for this IP6_MTU thing, and maybe other points we might use an obsolete dst ? Looking at the complexity of udpv6_sendmsg() and rawv6_sendmsg() I really wonder if it is worth extracting the route logic.
