linux-kernel - [PATCH] kunit: Set the current KUnit context when cleaning up

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Message-ID: <20230415091401.681395-1-davidgow@google.com>
Date:   Sat, 15 Apr 2023 17:14:01 +0800
From:   David Gow <davidgow@...gle.com>
To:     Brendan Higgins <brendan.higgins@...ux.dev>,
        Rae Moar <rmoar@...gle.com>,
        Daniel Latypov <dlatypov@...gle.com>, maxime@...no.tech,
        Benjamin Berg <benjamin@...solutions.net>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Gow <davidgow@...gle.com>
Subject: [PATCH] kunit: Set the current KUnit context when cleaning up

KUnit tests run in a kthread, with the current->kunit_test pointer set
to the test's context. This allows the kunit_get_current_test() and
kunit_fail_current_test() macros to work. Normally, this pointer is
still valid during test shutdown (i.e., the suite->exit function, and
any resource cleanup). However, if the test has exited early (e.g., due
to a failed assertion), the cleanup is done in the parent KUnit thread,
which does not have an active context.

Fix this by setting the active KUnit context for the duration of the
test shutdown procedure. When the test exits normally, this does
nothing. When run from the KUits previous value (probably NULL)
afterwards.

This should make it easier to get access to the KUnit context,
particularly from within resource cleanup functions, which may, for
example, need access to data in test->priv.

Signed-off-by: David Gow <davidgow@...gle.com>
---

This becomes useful with the current kunit_add_action() implementation,
as actions do not get the KUnit context passed in by default:
https://lore.kernel.org/linux-kselftest/CABVgOSmjs0wLUa4=ErkB9tH8p6A1P6N33befv63whF+hECRExQ@mail.gmail.com/

I think it's probably correct anyway, though, so we should either do
this, or totally rule out using kunit_get_current_test() here at all, by
resetting current->kunit_test to NULL before running cleanup even in
the normal case.

I've only given this the most cursory testing so far (I'm not sure how
much of the executor innards I want to expose to be able to actually
write a proper test for it), so more eyes and/or suggestions are
welcome.

Cheers,
-- David

---
 lib/kunit/test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index e2910b261112..2d7cad249863 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -392,10 +392,21 @@ static void kunit_case_internal_cleanup(struct kunit *test)
 static void kunit_run_case_cleanup(struct kunit *test,
 				   struct kunit_suite *suite)
 {
+	/*
+	 * If we're no-longer running from within the test kthread() because it failed
+	 * or timed out, we still need the context to be okay when running exit and
+	 * cleanup functions.
+	 */
+	struct kunit *old_current = current->kunit_test;
+
+	current->kunit_test = test;
 	if (suite->exit)
 		suite->exit(test);

 	kunit_case_internal_cleanup(test);
+
+	/* Restore the thread's previous test context (probably NULL or test). */
+	current->kunit_test = old_current;
 }

 struct kunit_try_catch_context {
-- 
2.40.0.634.g4ca3ef3211-goog