Lock standard output when composing log message (#15798)

Single log message is created by calling printf function multiple number
of times. In case of using log subsystem from more than one thread, the
log message might be corrupted. In order to prevent that, it is advised
to use flockfile()/funlockfile() for given stream.

src/platform/Linux/Logging.cpp

@@ -37,12 +37,18 @@ void ENFORCE_FORMAT(3, 0) LogV(const char * module, uint8_t category, const char
     // indicate the error occurred during getting time.
     gettimeofday(&tv, nullptr);
 
+    // Lock standard output, so a single log line will not be corrupted in case
+    // where multiple threads are using logging subsystem at the same time.
+    flockfile(stdout);
+
     printf("[%" PRIu64 ".%06" PRIu64 "][%lld:%lld] CHIP:%s: ", static_cast<uint64_t>(tv.tv_sec), static_cast<uint64_t>(tv.tv_usec),
            static_cast<long long>(syscall(SYS_getpid)), static_cast<long long>(syscall(SYS_gettid)), module);
     vprintf(msg, v);
     printf("\n");
     fflush(stdout);
 
+    funlockfile(stdout);
+
     // Let the application know that a log message has been emitted.
     DeviceLayer::OnLogOutput();
 }