kunit: tool: copy caller args in run_kernel to prevent mutation

run_kernel() appended KUnit flags directly to the caller-provided args
list. When exec_tests() calls run_kernel() repeatedly (e.g. with
--run_isolated), each call mutated the same list, causing later runs
to inherit stale filter_glob values and duplicate kunit.enable flags.

Fix this by copying args at the start of run_kernel(). Add a regression
test that calls run_kernel() twice with the same list and verifies the
original remains unchanged.

Fixes: ff9e09a ("kunit: tool: support running each suite/test separately")
Signed-off-by: Shuvam Pandey <shuvampandey1@gmail.com>
Reviewed-by: David Gow <david@davidgow.net>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: shuv-amp

tools/testing/kunit/kunit_kernel.py

@@ -346,8 +346,10 @@ def build_kernel(self, jobs: int, build_dir: str, make_options: Optional[List[st
 		return self.validate_config(build_dir)
 
 	def run_kernel(self, args: Optional[List[str]]=None, build_dir: str='', filter_glob: str='', filter: str='', filter_action: Optional[str]=None, timeout: Optional[int]=None) -> Iterator[str]:
-		if not args:
-			args = []
+		# Copy to avoid mutating the caller-supplied list. exec_tests() reuses
+		# the same args across repeated run_kernel() calls (e.g. --run_isolated),
+		# so appending to the original would accumulate stale flags on each call.
+		args = list(args) if args else []
 		if filter_glob:
 			args.append('kunit.filter_glob=' + filter_glob)
 		if filter:

tools/testing/kunit/kunit_tool_test.py

@@ -503,6 +503,32 @@ def fake_start(unused_args, unused_build_dir):
 			with open(kunit_kernel.get_outfile_path(build_dir), 'rt') as outfile:
 				self.assertEqual(outfile.read(), 'hi\nbye\n', msg='Missing some output')
 
+	def test_run_kernel_args_not_mutated(self):
+		"""Verify run_kernel() copies args so callers can reuse them."""
+		start_calls = []
+
+		def fake_start(start_args, unused_build_dir):
+			start_calls.append(list(start_args))
+			return subprocess.Popen(['printf', 'KTAP version 1\n'],
+						text=True, stdout=subprocess.PIPE)
+
+		with tempfile.TemporaryDirectory('') as build_dir:
+			tree = kunit_kernel.LinuxSourceTree(build_dir,
+					kunitconfig_paths=[os.devnull])
+			with mock.patch.object(tree._ops, 'start', side_effect=fake_start), \
+			     mock.patch.object(kunit_kernel.subprocess, 'call'):
+				kernel_args = ['mem=1G']
+				for _ in tree.run_kernel(args=kernel_args, build_dir=build_dir,
+							 filter_glob='suite.test1'):
+					pass
+				for _ in tree.run_kernel(args=kernel_args, build_dir=build_dir,
+							 filter_glob='suite.test2'):
+					pass
+				self.assertEqual(kernel_args, ['mem=1G'],
+					'run_kernel() should not modify caller args')
+				self.assertIn('kunit.filter_glob=suite.test1', start_calls[0])
+				self.assertIn('kunit.filter_glob=suite.test2', start_calls[1])
+
 	def test_build_reconfig_no_config(self):
 		with tempfile.TemporaryDirectory('') as build_dir:
 			with open(kunit_kernel.get_kunitconfig_path(build_dir), 'w') as f: