diff mbox series

[v2,3/3] kunit: tool: fix unintentional statefulness in run_kernel()

Message ID 20210204173045.1138504-4-dlatypov@google.com (mailing list archive)
State Superseded
Delegated to: Brendan Higgins
Headers show
Series kunit: support running subsets of test suites from kunit.py | expand

Commit Message

Daniel Latypov Feb. 4, 2021, 5:30 p.m. UTC 
This is a bug that has been present since the first version of this
code.
Using [] as a default parameter is dangerous, since it's mutable.

Example using the REPL:
>>> def bad(param = []):
...     param.append(len(param))
...     print(param)
...
>>> bad()
[0]
>>> bad()
[0, 1]

This wasn't a concern in the past since it would just keep appending the
same values to it.

E.g. before, `args` would just grow in size like:
  [mem=1G', 'console=tty']
  [mem=1G', 'console=tty', mem=1G', 'console=tty']

But with now filter_glob, this is more dangerous, e.g.
  run_kernel(filter_glob='my-test*') # default modified here
  run_kernel()			     # filter_glob still applies here!
That earlier `filter_glob` will affect all subsequent calls that don't
specify `args`.

Note: currently the kunit tool only calls run_kernel() at most once, so
it's not possible to trigger any negative side-effects right now.

Fixes: 6ebf5866f2e8 ("kunit: tool: add Python wrappers for running KUnit tests")
Signed-off-by: Daniel Latypov <dlatypov@google.com>
---
 tools/testing/kunit/kunit_kernel.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Brendan Higgins Feb. 4, 2021, 7:52 p.m. UTC | #1 
On Thu, Feb 4, 2021 at 9:31 AM Daniel Latypov <dlatypov@google.com> wrote:
>
> This is a bug that has been present since the first version of this
> code.
> Using [] as a default parameter is dangerous, since it's mutable.
>
> Example using the REPL:
> >>> def bad(param = []):
> ...     param.append(len(param))
> ...     print(param)
> ...
> >>> bad()
> [0]
> >>> bad()
> [0, 1]
>
> This wasn't a concern in the past since it would just keep appending the
> same values to it.
>
> E.g. before, `args` would just grow in size like:
>   [mem=1G', 'console=tty']
>   [mem=1G', 'console=tty', mem=1G', 'console=tty']
>
> But with now filter_glob, this is more dangerous, e.g.
>   run_kernel(filter_glob='my-test*') # default modified here
>   run_kernel()                       # filter_glob still applies here!
> That earlier `filter_glob` will affect all subsequent calls that don't
> specify `args`.
>
> Note: currently the kunit tool only calls run_kernel() at most once, so
> it's not possible to trigger any negative side-effects right now.
>
> Fixes: 6ebf5866f2e8 ("kunit: tool: add Python wrappers for running KUnit tests")
> Signed-off-by: Daniel Latypov <dlatypov@google.com>

Whoah, nice catch! I didn't even know that was a thing!

Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
diff mbox series

Patch

diff --git a/tools/testing/kunit/kunit_kernel.py b/tools/testing/kunit/kunit_kernel.py
index 71b1942f5ccd..6dd3cf6e8efa 100644
--- a/tools/testing/kunit/kunit_kernel.py
+++ b/tools/testing/kunit/kunit_kernel.py
@@ -199,7 +199,9 @@  class LinuxSourceTree(object):
 			return False
 		return self.validate_config(build_dir)
 
-	def run_kernel(self, args=[], build_dir='', filter_glob='', timeout=None) -> Iterator[str]:
+	def run_kernel(self, args=None, build_dir='', filter_glob='', timeout=None) -> Iterator[str]:
+		if not args:
+			args = []
 		args.extend(['mem=1G', 'console=tty'])
 		if filter_glob:
 			args.append('kunit.filter_glob='+filter_glob)