log_writer_file: do not call close() with mutex held

Generally not an issue, but if close() takes long, or even busy-loops due
to an underlying bug in the OS, it will block the main thread too.

src/modules/logger/log_writer_file.cpp

@@ -443,13 +443,19 @@ void LogWriterFile::run()
 
 						if (!buffer._should_run && written == static_cast<int>(available) && !is_part) {
 							/* Stop only when all data written */
+							pthread_mutex_unlock(&_mtx);
 							buffer.close_file();
+							pthread_mutex_lock(&_mtx);
+							buffer.reset();
 						}
 
 					} else {
 						PX4_ERR("write failed (%i)", errno);
 						buffer._should_run = false;
+						pthread_mutex_unlock(&_mtx);
 						buffer.close_file();
+						pthread_mutex_lock(&_mtx);
+						buffer.reset();
 					}
 
 				} else if (call_fsync && buffer._should_run) {
@@ -458,7 +464,10 @@ void LogWriterFile::run()
 					pthread_mutex_lock(&_mtx);
 
 				} else if (available == 0 && !buffer._should_run) {
+					pthread_mutex_unlock(&_mtx);
 					buffer.close_file();
+					pthread_mutex_lock(&_mtx);
+					buffer.reset();
 				}
 
 				/* if split into 2 parts, write the second part immediately as well */
@@ -687,12 +696,8 @@ ssize_t LogWriterFile::LogFileBuffer::write_to_file(const void *buffer, size_t s
 
 void LogWriterFile::LogFileBuffer::close_file()
 {
-	_head = 0;
-	_count = 0;
-
 	if (_fd >= 0) {
 		int res = close(_fd);
-		_fd = -1;
 
 		if (res) {
 			PX4_WARN("closing log file failed (%i)", errno);
@@ -703,5 +708,12 @@ void LogWriterFile::LogFileBuffer::close_file()
 	}
 }
 
+void LogWriterFile::LogFileBuffer::reset()
+{
+	_head = 0;
+	_count = 0;
+	_fd = -1;
+}
+
 }
 }

src/modules/logger/log_writer_file.h

@@ -171,6 +171,8 @@ private:
 
 		void close_file();
 
+		void reset();
+
 		size_t get_read_ptr(void **ptr, bool *is_part);
 
 		/**