Re: [PATCH net] route: check sysctl_fib_multipath_use_neigh earlier than hash

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Sun,  1 Apr 2018 22:40:35 +0800

> Prior to this patch, when one packet is hashed into path [1]
> (hash <= nh_upper_bound) and it's neigh is dead, it will try
> path [2]. However, if path [2]'s neigh is alive but it's
> hash > nh_upper_bound, it will not return this alive path.
> This packet will never be sent even if path [2] is alive.
> 
>  3.3.3.1/24:
>   nexthop via 1.1.1.254 dev eth1 weight 1 <--[1] (dead neigh)
>   nexthop via 2.2.2.254 dev eth2 weight 1 <--[2]
> 
> With sysctl_fib_multipath_use_neigh set is supposed to find an
> available path respecting to the l3/l4 hash. But if there is
> no available route with this hash, it should at least return
> an alive route even with other hash.
> 
> This patch is to fix it by processing fib_multipath_use_neigh
> earlier than the hash check, so that it will at least return
> an alive route if there is when fib_multipath_use_neigh is
> enabled. It's also compatible with before when there are alive
> routes with the l3/l4 hash.
> 
> Fixes: a6db4494d218 ("net: ipv4: Consider failed nexthops in multipath routes")
> Reported-by: Jianlin Shi <jishi@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks.