spawn: setup _exit finally block before fork

This is the most reliable way to handle the race condition.

1 files changed, 26 insertions, 17 deletions

diff --git a/pym/portage/process.py b/pym/portage/process.py
index a3461f474..fbfbde049 100644
--- a/pym/portage/process.py
+++ b/pym/portage/process.py
@@ -256,24 +256,33 @@ def spawn(mycommand, env={}, opt_name=None, fd_pipes=None, returnpid=False,
 		fd_pipes[1] = pw
 		fd_pipes[2] = pw
 
-	pid = os.fork()
+	parent_pid = os.getpid()
+	pid = None
+	try:
+		pid = os.fork()
 
-	if pid == 0:
-		try:
-			_exec(binary, mycommand, opt_name, fd_pipes,
-			      env, gid, groups, uid, umask, pre_exec)
-		except SystemExit:
-			raise
-		except Exception as e:
-			# We need to catch _any_ exception so that it doesn't
-			# propagate out of this function and cause exiting
-			# with anything other than os._exit()
-			writemsg("%s:\n   %s\n" % (e, " ".join(mycommand)), noiselevel=-1)
-			traceback.print_exc()
-			sys.stderr.flush()
-		finally:
-			# Call os._exit() from finally block, in order to suppress any
-			# finally blocks from earlier in the call stack. See bug #345289.
+		if pid == 0:
+			try:
+				_exec(binary, mycommand, opt_name, fd_pipes,
+					env, gid, groups, uid, umask, pre_exec)
+			except SystemExit:
+				raise
+			except Exception as e:
+				# We need to catch _any_ exception so that it doesn't
+				# propagate out of this function and cause exiting
+				# with anything other than os._exit()
+				writemsg("%s:\n   %s\n" % (e, " ".join(mycommand)),
+					noiselevel=-1)
+				traceback.print_exc()
+				sys.stderr.flush()
+
+	finally:
+		if pid == 0 or (pid is None and os.getpid() != parent_pid):
+			# Call os._exit() from a finally block in order
+			# to suppress any finally blocks from earlier
+			# in the call stack (see bug #345289). This
+			# finally block has to be setup before the fork
+			# in order to avoid a race condition.
 			os._exit(1)
 
 	if not isinstance(pid, int):