Fix concurrency issues in controlclient, ipn, types/logger (#456)

Signed-Off-By: Dmytro Shynkevych <dmytro@tailscale.com>

types/logger/logger.go

@@ -127,18 +127,23 @@ func RateLimitedFn(logf Logf, f time.Duration, burst int, maxCache int) Logf {
 // since the last time this identical line was logged.
 func LogOnChange(logf Logf, maxInterval time.Duration, timeNow func() time.Time) Logf {
 	var (
+		mu          sync.Mutex
 		sLastLogged string
 		tLastLogged = timeNow()
 	)
 
 	return func(format string, args ...interface{}) {
 		s := fmt.Sprintf(format, args...)
+
+		mu.Lock()
 		if s == sLastLogged && timeNow().Sub(tLastLogged) < maxInterval {
+			mu.Unlock()
 			return
 		}
-
 		sLastLogged = s
 		tLastLogged = timeNow()
+		mu.Unlock()
+
 		logf(s)
 	}
 

types/logger/logger_test.go

@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"fmt"
 	"log"
+	"sync"
 	"testing"
 	"time"
 )
@@ -117,3 +118,31 @@ func TestArgWriter(t *testing.T) {
 		t.Errorf("got %q; want %q", got, want)
 	}
 }
+
+func TestSynchronization(t *testing.T) {
+	timeNow := testTimer(1 * time.Second)
+	tests := []struct {
+		name string
+		logf Logf
+	}{
+		{"RateLimitedFn", RateLimitedFn(t.Logf, 1*time.Minute, 2, 50)},
+		{"LogOnChange", LogOnChange(t.Logf, 5*time.Second, timeNow)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var wg sync.WaitGroup
+			wg.Add(2)
+
+			f := func() {
+				tt.logf("1 2 3 4 5")
+				wg.Done()
+			}
+
+			go f()
+			go f()
+
+			wg.Wait()
+		})
+	}
+}