From: Ido Schimmel Date: Thu, 11 Jun 2026 15:46:03 +0000 (+0300) Subject: ipv6: Select best matching nexthop object in fib6_table_lookup() X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=484bb9d164df397a53e0f533b262b27b1590efcb;p=thirdparty%2Flinux.git ipv6: Select best matching nexthop object in fib6_table_lookup() Currently, when using multipath routes without nexthop objects, fib6_table_lookup() selects the nexthop with the highest score. This means that when both a source address and an oif are specified, the nexthop that is chosen is the one that matches in terms of oif: # sysctl -wq net.ipv6.conf.all.forwarding=1 # ip address add 2001:db8:2::1/64 dev lo # ip route add 2001:db8:10::/64 nexthop via fe80::1 dev dummy1 nexthop via fe80::2 dev dummy2 # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:10::${i} from 2001:db8:2::1 oif dummy1; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy1 # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:10::${i} from 2001:db8:2::1 oif dummy2; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy2 When using nexthop objects, fib6_table_lookup() selects the first matching nexthop and not necessarily the one with the highest score: # ip nexthop add id 1 via fe80::1 dev dummy1 # ip nexthop add id 2 via fe80::2 dev dummy2 # ip nexthop add id 3 group 1/2 # ip route add 2001:db8:20::/64 nhid 3 # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:20::${i} from 2001:db8:2::1 oif dummy1; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy1 # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:20::${i} from 2001:db8:2::1 oif dummy2; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy1 This is not very significant right now because the nexthop is later overwritten during path selection in fib6_select_path(). However, the next patch is going to skip path selection when we have an oif match during output route lookup. As a preparation for this change, align the nexthop object behavior with the legacy one and make sure that fib6_table_lookup() always selects the best matching nexthop. Do that by always returning 0 from rt6_nh_find_match() in order not to terminate the loop in nexthop_for_each_fib6_nh() and storing in arg->nh the best matching nexthop so far. Behavior after the change: # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:20::${i} from 2001:db8:2::1 oif dummy1; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy1 # perf record -e fib6:fib6_table_lookup -- bash -c "for i in {1..100}; do ip route get 2001:db8:20::${i} from 2001:db8:2::1 oif dummy2; done > /dev/null" # perf script | grep -o dummy[0-9] | sort | uniq -c 100 dummy2 Signed-off-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/20260611154605.992528-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 8259c7527aa4..09dac3aa8778 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -819,9 +819,11 @@ static int rt6_nh_find_match(struct fib6_nh *nh, void *_arg) { struct fib6_nh_frl_arg *arg = _arg; - arg->nh = nh; - return find_match(nh, arg->flags, arg->oif, arg->strict, - arg->mpri, arg->do_rr); + if (find_match(nh, arg->flags, arg->oif, arg->strict, arg->mpri, + arg->do_rr)) + arg->nh = nh; + + return 0; } static void __find_rr_leaf(struct fib6_info *f6i_start, @@ -861,11 +863,10 @@ static void __find_rr_leaf(struct fib6_info *f6i_start, res->nh = nexthop_fib6_nh(f6i->nh); return; } - if (nexthop_for_each_fib6_nh(f6i->nh, rt6_nh_find_match, - &arg)) { - matched = true; - nh = arg.nh; - } + nexthop_for_each_fib6_nh(f6i->nh, rt6_nh_find_match, + &arg); + matched = !!arg.nh; + nh = arg.nh; } else { nh = f6i->fib6_nh; if (find_match(nh, f6i->fib6_flags, oif, strict,