Do not acquire lock for file.Sync() fsync call

klog.go

@@ -1012,6 +1012,7 @@ func (l *loggingT) exit(err error) {
 		return
 	}
 	l.flushAll()
+	l.syncAll()
 	OsExit(2)
 }
 
@@ -1225,24 +1226,36 @@ func (l *loggingT) lockAndFlushAll() {
 	l.mu.Lock()
 	l.flushAll()
 	l.mu.Unlock()
+	// Some environments are slow when syncing and holding the lock might cause contention.
+	l.syncAll()
 }
 
-// flushAll flushes all the logs and attempts to "sync" their data to disk.
+// flushAll flushes all the logs
 // l.mu is held.
 func (l *loggingT) flushAll() {
 	// Flush from fatal down, in case there's trouble flushing.
 	for s := severity.FatalLog; s >= severity.InfoLog; s-- {
 		file := l.file[s]
 		if file != nil {
 			_ = file.Flush() // ignore error
-			_ = file.Sync()  // ignore error
 		}
 	}
 	if logging.loggerOptions.flush != nil {
 		logging.loggerOptions.flush()
 	}
 }
 
+// syncAll attempts to "sync" their data to disk.
+func (l *loggingT) syncAll() {
+	// Flush from fatal down, in case there's trouble flushing.
+	for s := severity.FatalLog; s >= severity.InfoLog; s-- {
+		file := l.file[s]
+		if file != nil {
+			_ = file.Sync() // ignore error
+		}
+	}
+}
+
 // CopyStandardLogTo arranges for messages written to the Go "log" package's
 // default logs to also appear in the Google logs for the named and lower
 // severities.  Subsequent changes to the standard log's default output location