wgengine: remove all peer status from open timeout diagnostics

Avoid contention from fetching status for all peers, and instead fetch
status for a single peer.

Updates tailscale/coral#72
Signed-off-by: James Tucker <james@tailscale.com>

wgengine/pendopen.go

@@ -9,7 +9,6 @@
 	"runtime"
 	"time"
 
-	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/flowtrack"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/tsaddr"
@@ -157,28 +156,8 @@ func (e *userspaceEngine) onOpenTimeout(flow flowtrack.Tuple) {
 		return
 	}
 
-	// We don't care if this information is perfectly up-to-date, since
-	// we're just using it to print debug information.
-	//
-	// In tailscale/coral#72, we see a goroutine profile with thousands of
-	// goroutines blocked on the mutex in getStatus here, so we wrap it in
-	// a singleflight and accept stale information to reduce contention.
-	st, err, _ := e.getStatusSf.Do(struct{}{}, e.getStatus)
-
-	var ps *ipnstate.PeerStatusLite
-	if err == nil {
-		for _, v := range st.Peers {
-			if v.NodeKey == n.Key {
-				v := v // copy
-				ps = &v
-				break
-			}
-		}
-	} else {
-		e.logf("open-conn-track: timeout opening %v to node %v; failed to get engine status: %v", flow, n.Key.ShortString(), err)
-		return
-	}
-	if ps == nil {
+	ps, found := e.getPeerStatusLite(n.Key)
+	if !found {
 		onlyZeroRoute := true // whether peerForIP returned n only because its /0 route matched
 		for _, r := range n.AllowedIPs {
 			if r.Bits() != 0 && r.Contains(flow.Dst.Addr()) {

wgengine/userspace.go

@@ -982,25 +982,30 @@ func (e *userspaceEngine) getStatusCallback() StatusCallback {
 
 var ErrEngineClosing = errors.New("engine closing; no status")
 
+func (e *userspaceEngine) getPeerStatusLite(pk key.NodePublic) (status ipnstate.PeerStatusLite, ok bool) {
+	e.wgLock.Lock()
+	if e.wgdev == nil {
+		e.wgLock.Unlock()
+		return status, false
+	}
+	peer := e.wgdev.LookupPeer(pk.Raw32())
+	e.wgLock.Unlock()
+	if peer == nil {
+		return status, false
+	}
+	status.NodeKey = pk
+	status.RxBytes = int64(wgint.PeerRxBytes(peer))
+	status.TxBytes = int64(wgint.PeerTxBytes(peer))
+	status.LastHandshake = time.Unix(0, wgint.PeerLastHandshakeNano(peer))
+	return status, true
+}
+
 func (e *userspaceEngine) getStatus() (*Status, error) {
 	// Grab derpConns before acquiring wgLock to not violate lock ordering;
 	// the DERPs method acquires magicsock.Conn.mu.
 	// (See comment in userspaceEngine's declaration.)
 	derpConns := e.magicConn.DERPs()
 
-	e.wgLock.Lock()
-	wgdev := e.wgdev
-	e.wgLock.Unlock()
-
-	// Assume that once created, wgdev is typically not replaced in-flight.
-	if wgdev == nil {
-		// RequestStatus was invoked before the wgengine has
-		// finished initializing. This can happen when wgegine
-		// provides a callback to magicsock for endpoint
-		// updates that calls RequestStatus.
-		return nil, nil
-	}
-
 	e.mu.Lock()
 	closing := e.closing
 	peerKeys := make([]key.NodePublic, len(e.peerSequence))
@@ -1013,18 +1018,9 @@ func (e *userspaceEngine) getStatus() (*Status, error) {
 
 	peers := make([]ipnstate.PeerStatusLite, 0, len(peerKeys))
 	for _, key := range peerKeys {
-		// LookupPeer is internally locked in wgdev.
-		peer := wgdev.LookupPeer(key.Raw32())
-		if peer == nil {
-			continue
+		if status, found := e.getPeerStatusLite(key); found {
+			peers = append(peers, status)
 		}
-
-		var p ipnstate.PeerStatusLite
-		p.NodeKey = key
-		p.RxBytes = int64(wgint.PeerRxBytes(peer))
-		p.TxBytes = int64(wgint.PeerTxBytes(peer))
-		p.LastHandshake = time.Unix(0, wgint.PeerLastHandshakeNano(peer))
-		peers = append(peers, p)
 	}
 
 	return &Status{

wgengine/watchdog_test.go

@@ -5,14 +5,9 @@
 package wgengine
 
 import (
-	"fmt"
-	"regexp"
 	"runtime"
-	"strings"
 	"testing"
 	"time"
-
-	"tailscale.com/tstest"
 )
 
 func TestWatchdog(t *testing.T) {
@@ -42,49 +37,4 @@ func TestWatchdog(t *testing.T) {
 		e.RequestStatus()
 		e.Close()
 	})
-
-	t.Run("watchdog fires on blocked getStatus", func(t *testing.T) {
-		t.Parallel()
-		e, err := NewFakeUserspaceEngine(t.Logf, 0)
-		if err != nil {
-			t.Fatal(err)
-		}
-		t.Cleanup(e.Close)
-		usEngine := e.(*userspaceEngine)
-		e = NewWatchdog(e)
-		wdEngine := e.(*watchdogEngine)
-		wdEngine.maxWait = maxWaitMultiple * 100 * time.Millisecond
-
-		logBuf := new(tstest.MemLogger)
-		fatalCalled := make(chan struct{})
-		wdEngine.logf = logBuf.Logf
-		wdEngine.fatalf = func(format string, args ...any) {
-			t.Logf("FATAL: %s", fmt.Sprintf(format, args...))
-			fatalCalled <- struct{}{}
-		}
-
-		usEngine.wgLock.Lock() // blocks getStatus so the watchdog will fire
-
-		go e.RequestStatus()
-
-		select {
-		case <-fatalCalled:
-			logs := logBuf.String()
-			if !strings.Contains(logs, "goroutine profile: total ") {
-				t.Errorf("fatal called without watchdog stacks, got: %s", logs)
-			}
-			re := regexp.MustCompile(`(?m)^\s*in-flight\[\d+\]: name=RequestStatus duration=.* start=.*$`)
-			if !re.MatchString(logs) {
-				t.Errorf("fatal called without in-flight list, got: %s", logs)
-			}
-
-			// expected
-		case <-time.After(3 * time.Second):
-			t.Fatalf("watchdog failed to fire")
-		}
-
-		usEngine.wgLock.Unlock()
-		wdEngine.fatalf = t.Fatalf
-		wdEngine.Close()
-	})
 }