From 9e68841939170ae132935e26e5e200066b1f62c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Claus=20Lensb=C3=B8l?= <claus@tailscale.com>
Date: Wed, 8 Apr 2026 09:01:07 -0400
Subject: [PATCH] control/controlclient: avoid calls to ms.netmap() (#19281)
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Instead of generating the full netmap, just fetch the peers out the the
existing peers map.

The extra usage was introduced with netmap caching, but there is no need
to call the netmap to get this information, rather the existing peermap
can be used.

Updates #12639

Signed-off-by: Claus Lensbøl <claus@tailscale.com>
---
 control/controlclient/map.go      | 24 ++++++++++--------------
 control/controlclient/map_test.go |  7 +++----
 2 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/control/controlclient/map.go b/control/controlclient/map.go
index 4c58ae8af..c8cbdbce5 100644
--- a/control/controlclient/map.go
+++ b/control/controlclient/map.go
@@ -408,10 +408,9 @@ type updateStats struct {
 // removeUnwantedDiscoUpdates goes over the patchified updates and reject items
 // where the node is offline and has last been seen before the recorded last seen.
 func (ms *mapSession) removeUnwantedDiscoUpdates(resp *tailcfg.MapResponse) {
-	existingMap := ms.netmap()
-	if existingMap == nil {
-		return
-	}
+	ms.peersMu.RLock()
+	defer ms.peersMu.RUnlock()
+
 	acceptedDiscoUpdates := resp.PeersChangedPatch[:0]
 
 	for _, change := range resp.PeersChangedPatch {
@@ -430,14 +429,13 @@ func (ms *mapSession) removeUnwantedDiscoUpdates(resp *tailcfg.MapResponse) {
 			continue
 		}
 
-		peerIdx := existingMap.PeerIndexByNodeID(change.NodeID)
+		existingNode, ok := ms.peers[change.NodeID]
 		// Accept if:
 		// - Cannot find the peer, don't have enough data
-		if peerIdx < 0 {
+		if !ok {
 			acceptedDiscoUpdates = append(acceptedDiscoUpdates, change)
 			continue
 		}
-		existingNode := existingMap.Peers[peerIdx]
 
 		// Accept if:
 		// - lastSeen moved forward in time.
@@ -456,13 +454,12 @@ func (ms *mapSession) removeUnwantedDiscoUpdates(resp *tailcfg.MapResponse) {
 // local netmap has a newer key learned via TSMP, overwrite the update with the
 // key from TSMP.
 func (ms *mapSession) removeUnwantedDiscoUpdatesFromFullNetmapUpdate(resp *tailcfg.MapResponse) {
+	ms.peersMu.RLock()
+	defer ms.peersMu.RUnlock()
+
 	if len(resp.Peers) == 0 {
 		return
 	}
-	existingMap := ms.netmap()
-	if existingMap == nil {
-		return
-	}
 	for _, peer := range resp.Peers {
 		if peer.DiscoKey.IsZero() {
 			continue
@@ -470,14 +467,13 @@ func (ms *mapSession) removeUnwantedDiscoUpdatesFromFullNetmapUpdate(resp *tailc
 
 		// Accept if:
 		// - peer is new
-		peerIdx := existingMap.PeerIndexByNodeID(peer.ID)
-		if peerIdx < 0 {
+		existingNode, ok := ms.peers[peer.ID]
+		if !ok {
 			continue
 		}
 
 		// Accept if:
 		// - disco key has not changed
-		existingNode := existingMap.Peers[peerIdx]
 		if existingNode.DiscoKey() == peer.DiscoKey {
 			continue
 		}
diff --git a/control/controlclient/map_test.go b/control/controlclient/map_test.go
index 5eee931f3..f057345d9 100644
--- a/control/controlclient/map_test.go
+++ b/control/controlclient/map_test.go
@@ -696,13 +696,12 @@ func TestUpdateDiscoForNode(t *testing.T) {
 			ms.updateDiscoForNode(node.ID, node.Key, newKey.Public(), tt.updateLastSeen, tt.updateOnline)
 			<-nu.done
 
-			nm := ms.netmap()
-			peerIdx := nm.PeerIndexByNodeID(node.ID)
-			if peerIdx == -1 {
+			peer, ok := ms.peers[node.ID]
+			if !ok {
 				t.Fatal("node not found")
 			}
 
-			updated := nm.Peers[peerIdx].DiscoKey().Compare(newKey.Public()) == 0
+			updated := peer.DiscoKey().Compare(newKey.Public()) == 0
 			if updated != tt.wantUpdate {
 				t.Fatalf("Disco key update: %t, wanted update: %t", updated, tt.wantUpdate)
 			}