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

Commit Message

Gilad Naaman Oct. 28, 2024, 8:10 a.m. UTC

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 <[e-mail]>
---
 net/sctp/protocol.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Patch

diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index 39ca5403d4d7..2e548961b740 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) {