[PATCH net-next 6/6] ipv6: avoid cache line dirtying in ipv6_dev_get_saddr()

[Eric Dumazet]

By extending the rcu section a bit, we can avoid these
very expensive in6_ifa_put()/in6_ifa_hold() calls
done in __ipv6_dev_get_saddr() and ipv6_dev_get_saddr()

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/ipv6/addrconf.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 
20c3ca777529fc49ebf749ca6f7d8c2451258d55..cab3faad2bf1354c1241a11ac27178ea675aed55
 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1608,11 +1608,6 @@ static int __ipv6_dev_get_saddr(struct net *net,
                                }
                                break;
                        } else if (minihiscore < miniscore) {
-                               if (hiscore->ifa)
-                                       in6_ifa_put(hiscore->ifa);
-
-                               in6_ifa_hold(score->ifa);
-
                                swap(hiscore, score);
                                hiscore_idx = 1 - hiscore_idx;
 
@@ -1660,6 +1655,7 @@ int ipv6_dev_get_saddr(struct net *net, const struct 
net_device *dst_dev,
        int dst_type;
        bool use_oif_addr = false;
        int hiscore_idx = 0;
+       int ret = 0;
 
        dst_type = __ipv6_addr_type(daddr);
        dst.addr = daddr;
@@ -1735,15 +1731,14 @@ int ipv6_dev_get_saddr(struct net *net, const struct 
net_device *dst_dev,
        }
 
 out:
-       rcu_read_unlock();
-
        hiscore = &scores[hiscore_idx];
        if (!hiscore->ifa)
-               return -EADDRNOTAVAIL;
+               ret = -EADDRNOTAVAIL;
+       else
+               *saddr = hiscore->ifa->addr;
 
-       *saddr = hiscore->ifa->addr;
-       in6_ifa_put(hiscore->ifa);
-       return 0;
+       rcu_read_unlock();
+       return ret;
 }
 EXPORT_SYMBOL(ipv6_dev_get_saddr);
 
-- 
2.14.2.920.gcf0c67979c-goog