ipv6: remove one read_lock()/read_unlock() pair in rt6_check_neigh()

commit c486640aa710ddd06c13a7f7162126e1552e8842 upstream.

rt6_check_neigh() uses read_lock() to protect n->nud_state reading.

This seems overkill and causes false sharing.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 0a9f854bfa50c1ef6d3da6db4c9a8a19eddc141a..0bcdb675ba2c190b82919767b726ca6c795e3449 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -690,16 +690,16 @@ static enum rt6_nud_state rt6_check_neigh(const struct fib6_nh *fib6_nh)
        neigh = __ipv6_neigh_lookup_noref(fib6_nh->fib_nh_dev,
                                          &fib6_nh->fib_nh_gw6);
        if (neigh) {
-               read_lock(&neigh->lock);
-               if (neigh->nud_state & NUD_VALID)
+               u8 nud_state = READ_ONCE(neigh->nud_state);
+
+               if (nud_state & NUD_VALID)
                        ret = RT6_NUD_SUCCEED;
 #ifdef CONFIG_IPV6_ROUTER_PREF
-               else if (!(neigh->nud_state & NUD_FAILED))
+               else if (!(nud_state & NUD_FAILED))
                        ret = RT6_NUD_SUCCEED;
                else
                        ret = RT6_NUD_FAIL_PROBE;
 #endif
-               read_unlock(&neigh->lock);
        } else {
                ret = IS_ENABLED(CONFIG_IPV6_ROUTER_PREF) ?
                      RT6_NUD_SUCCEED : RT6_NUD_FAIL_DO_RR;