log_writer_file: fix race condition for fast consecutive stop & start calls

src/modules/logger/log_writer_file.cpp

@@ -83,6 +83,18 @@ LogWriterFile::~LogWriterFile()
 
 void LogWriterFile::start_log(LogType type, const char *filename)
 {
+	// At this point we don't expect the file to be open, but it can happen for very fast consecutive stop & start
+	// calls. In that case we wait for the thread to close the file first.
+	lock();
+
+	while (_buffers[(int)type].fd() >= 0) {
+		unlock();
+		system_usleep(5000);
+		lock();
+	}
+
+	unlock();
+
 	if (type == LogType::Full) {
 		// register the current file with the hardfault handler: if the system crashes,
 		// the hardfault handler will append the crash log to that file on the next reboot.