Hello,
On Fri, 1 Apr 2016, David Ahern wrote:
> v3
> - Julian comments: changed use of dead in documentation to failed,
> init state to NUD_REACHABLE which simplifies fib_good_nh, use of
> nh_dev for neighbor lookup, fallback to first entry which is what
> current logic does
>
> v2
> - use rcu locking to avoid refcnts per Eric's suggestion
> - only consider neighbor info for nh_scope == RT_SCOPE_LINK per Julian's
> comment
> - drop the 'state == NUD_REACHABLE' from the state check since it is
> part of NUD_VALID (comment from Julian)
> - wrapped the use of the neigh in a sysctl
>
> Documentation/networking/ip-sysctl.txt | 10 ++++++++++
> include/net/netns/ipv4.h | 3 +++
> net/ipv4/fib_semantics.c | 32 ++++++++++++++++++++++++++++----
> net/ipv4/sysctl_net_ipv4.c | 11 +++++++++++
> 4 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index d97268e8ff10..e08abf96824a 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -1559,21 +1559,45 @@ int fib_sync_up(struct net_device *dev, unsigned int
> nh_flags)
> }
>
> #ifdef CONFIG_IP_ROUTE_MULTIPATH
> +static bool fib_good_nh(const struct fib_nh *nh)
> +{
> + int state = NUD_REACHABLE;
> +
> + if (nh->nh_scope == RT_SCOPE_LINK) {
> + struct neighbour *n = NULL;
NULL is not needed anymore.
> +
> + rcu_read_lock_bh();
> +
> + n = __neigh_lookup_noref(&arp_tbl, &nh->nh_gw, nh->nh_dev);
> + if (n)
> + state = n->nud_state;
> +
> + rcu_read_unlock_bh();
> + }
> +
> + return !!(state & NUD_VALID);
> +}
>
> void fib_select_multipath(struct fib_result *res, int hash)
> {
> struct fib_info *fi = res->fi;
> + struct net *net = fi->fib_net;
> + unsigned char first_nhsel = 0;
Looking at fib_table_lookup() res->nh_sel is not 0
in all cases. I personally don't like that we do not
fallback properly but to make this logic more correct we
can use something like this:
bool first = false;
>
> for_nexthops(fi) {
> if (hash > atomic_read(&nh->nh_upper_bound))
> continue;
>
> - res->nh_sel = nhsel;
> - return;
> + if (!net->ipv4.sysctl_fib_multipath_use_neigh ||
> + fib_good_nh(nh)) {
> + res->nh_sel = nhsel;
> + return;
> + }
> + if (!first_nhsel)
> + first_nhsel = nhsel;
if (!first) {
res->nh_sel = nhsel;
first = true;
}
> } endfor_nexthops(fi);
>
> - /* Race condition: route has just become dead. */
> - res->nh_sel = 0;
> + res->nh_sel = first_nhsel;
And then this is not needed anymore. Even setting
to 0 was not needed because 0 is not better than current
nh_sel when both are DEAD/LINKDOWN.
Regards
--
Julian Anastasov <j...@ssi.bg>
