bitbake: bitbake-worker: Fix silent hang issue caused by unexpected stdout content

This patch addresses an issue in bitbake-worker where stdout,
reserved for status reporting, is improperly accessed by child processes.

The problem occurs during the execution of parseRecipe,
which calls anonymous functions. If these functions use print-like operations,
they can inadvertently output data to stdout. This unexpected data can cause
the runqueue to hang silently, if the stdout buffer is flushed
before exec_task is executed.

To prevent this, the patch redirects stdout to /dev/null and ensures it is
flushed prior to the execution of exec_task.

(Bitbake rev: 08f3e677d6af27a41a918aaa9da9c1c9b20a0b95)

Signed-off-by: Yang Xu <yang.xu@mediatek.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake-worker

@@ -237,9 +237,11 @@ def fork_off_task(cfg, data, databuilder, workerdata, extraconfigdata, runtask):
             # Let SIGHUP exit as SIGTERM
             signal.signal(signal.SIGHUP, sigterm_handler)
 
-            # No stdin
-            newsi = os.open(os.devnull, os.O_RDWR)
-            os.dup2(newsi, sys.stdin.fileno())
+            # No stdin & stdout
+            # stdout is used as a status report channel and must not be used by child processes.
+            dumbio = os.open(os.devnull, os.O_RDWR)
+            os.dup2(dumbio, sys.stdin.fileno())
+            os.dup2(dumbio, sys.stdout.fileno())
 
             if umask is not None:
                 os.umask(umask)
@@ -305,6 +307,10 @@ def fork_off_task(cfg, data, databuilder, workerdata, extraconfigdata, runtask):
                 if not quieterrors:
                     logger.critical(traceback.format_exc())
                 os._exit(1)
+
+            sys.stdout.flush()
+            sys.stderr.flush()
+
             try:
                 if dry_run:
                     return 0