[PATCH net-next v2] sctp: Avoid enqueuing addr events redundantly

[Gilad Naaman <gnaaman@xxxxxxxxxxxxx>]

Avoid modifying or enqueuing new events if it's possible to tell that no
one will consume them.

Since enqueueing requires searching the current queue for opposite
events for the same address, adding addresses en-masse turns this
inetaddr_event into a bottle-neck, as it will get slower and slower
with each address added.

Signed-off-by: Gilad Naaman <gnaaman@xxxxxxxxxxxxx>
---
Changes in v2:
 - Reorder list removal to avoid race with new sessions
---
 net/sctp/ipv6.c     |  2 +-
 net/sctp/protocol.c | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index f7b809c0d142..b96c849545ae 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -103,10 +103,10 @@ static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
 			    ipv6_addr_equal(&addr->a.v6.sin6_addr,
 					    &ifa->addr) &&
 			    addr->a.v6.sin6_scope_id == ifa->idev->dev->ifindex) {
-				sctp_addr_wq_mgmt(net, addr, SCTP_ADDR_DEL);
 				found = 1;
 				addr->valid = 0;
 				list_del_rcu(&addr->list);
+				sctp_addr_wq_mgmt(net, addr, SCTP_ADDR_DEL);
 				break;
 			}
 		}
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index 39ca5403d4d7..8b9a1b96695e 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -738,6 +738,20 @@ void sctp_addr_wq_mgmt(struct net *net, struct sctp_sockaddr_entry *addr, int cm
 	 */
 
 	spin_lock_bh(&net->sctp.addr_wq_lock);
+
+	/* Avoid searching the queue or modifying it if there are no consumers,
+	 * as it can lead to performance degradation if addresses are modified
+	 * en-masse.
+	 *
+	 * If the queue already contains some events, update it anyway to avoid
+	 * ugly races between new sessions and new address events.
+	 */
+	if (list_empty(&net->sctp.auto_asconf_splist) &&
+	    list_empty(&net->sctp.addr_waitq)) {
+		spin_unlock_bh(&net->sctp.addr_wq_lock);
+		return;
+	}
+
 	/* Offsets existing events in addr_wq */
 	addrw = sctp_addr_wq_lookup(net, addr);
 	if (addrw) {
@@ -808,10 +822,10 @@ static int sctp_inetaddr_event(struct notifier_block *this, unsigned long ev,
 			if (addr->a.sa.sa_family == AF_INET &&
 					addr->a.v4.sin_addr.s_addr ==
 					ifa->ifa_local) {
-				sctp_addr_wq_mgmt(net, addr, SCTP_ADDR_DEL);
 				found = 1;
 				addr->valid = 0;
 				list_del_rcu(&addr->list);
+				sctp_addr_wq_mgmt(net, addr, SCTP_ADDR_DEL);
 				break;
 			}
 		}
-- 
2.34.1