fix sync.Once usage instead of adding a mutex lock

entry.go

@@ -156,20 +156,23 @@ func getPackageName(f string) string {
 
 // getCaller retrieves the name of the first non-logrus calling function
 func getCaller() *runtime.Frame {
+
+	// cache this package's fully-qualified name
+	callerInitOnce.Do(func() {
+		pcs := make([]uintptr, 2)
+		_ = runtime.Callers(0, pcs)
+		logrusPackage = getPackageName(runtime.FuncForPC(pcs[1]).Name())
+
+		// now that we have the cache, we can skip a minimum count of known-logrus functions
+		// XXX this is dubious, the number of frames may vary
+		minimumCallerDepth = knownLogrusFrames
+	})
+
 	// Restrict the lookback frames to avoid runaway lookups
 	pcs := make([]uintptr, maximumCallerDepth)
 	depth := runtime.Callers(minimumCallerDepth, pcs)
 	frames := runtime.CallersFrames(pcs[:depth])
 
-	// cache this package's fully-qualified name
-	callerInitOnce.Do(func() {
-		logrusPackage = getPackageName(runtime.FuncForPC(pcs[0]).Name())
-
-		// now that we have the cache, we can skip a minimum count of known-logrus functions
-		// XXX this is dubious, the number of frames may vary store an entry in a logger interface
-		minimumCallerDepth = knownLogrusFrames
-	})
-
 	for f, again := frames.Next(); again; f, again = frames.Next() {
 		pkg := getPackageName(f.Function)
 
@@ -206,9 +209,7 @@ func (entry Entry) log(level Level, msg string) {
 	entry.Level = level
 	entry.Message = msg
 	if entry.Logger.ReportCaller {
-		entry.Logger.mu.Lock()
 		entry.Caller = getCaller()
-		entry.Logger.mu.Unlock()
 	}
 
 	entry.fireHooks()