[PATCH v3 1/4] kunit: Always run cleanup from a test kthread

[David Gow <davidgow@google.com>]

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.

Instead, in the event test terminates early, run the test exit and
cleanup from a new 'cleanup' kthread, which sets current->kunit_test,
and better isolates the rest of KUnit from issues which arise in test
cleanup.

If a test cleanup function itself aborts (e.g., due to an assertion
failing), there will be no further attempts to clean up: an error will
be logged and the test failed. For example:
	 # example_simple_test: test aborted during cleanup. continuing without cleaning up

This should also 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@google.com>
---

This is an updated version of / replacement of "kunit: Set the current
KUnit context when cleaning up", which instead creates a new kthread
for cleanup tasks if the original test kthread is aborted. This protects
us from failed assertions during cleanup, if the test exited early.

Changes since v2:
https://lore.kernel.org/linux-kselftest/20230419085426.1671703-1-davidgow@google.com/
- Always run cleanup in its own kthread
  - Therefore, never attempt to re-run it if it exits
  - Thanks, Benjamin.
Changes since v1:
https://lore.kernel.org/linux-kselftest/20230415091401.681395-1-davidgow@google.com/
- Move cleanup execution to another kthread
  - (Thanks, Benjamin, for pointing out the assertion issues)

---
 lib/kunit/test.c | 55 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index e2910b261112..2025e51941e6 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -419,10 +419,50 @@ static void kunit_try_run_case(void *data)
 	 * thread will resume control and handle any necessary clean up.
 	 */
 	kunit_run_case_internal(test, suite, test_case);
-	/* This line may never be reached. */
+}
+
+static void kunit_try_run_case_cleanup(void *data)
+{
+	struct kunit_try_catch_context *ctx = data;
+	struct kunit *test = ctx->test;
+	struct kunit_suite *suite = ctx->suite;
+
+	current->kunit_test = test;
+
 	kunit_run_case_cleanup(test, suite);
 }
 
+static void kunit_catch_run_case_cleanup(void *data)
+{
+	struct kunit_try_catch_context *ctx = data;
+	struct kunit *test = ctx->test;
+	int try_exit_code = kunit_try_catch_get_result(&test->try_catch);
+
+	/* It is always a failure if cleanup aborts. */
+	kunit_set_failure(test);
+
+	if (try_exit_code) {
+		/*
+		 * Test case could not finish, we have no idea what state it is
+		 * in, so don't do clean up.
+		 */
+		if (try_exit_code == -ETIMEDOUT) {
+			kunit_err(test, "test case cleanup timed out\n");
+		/*
+		 * Unknown internal error occurred preventing test case from
+		 * running, so there is nothing to clean up.
+		 */
+		} else {
+			kunit_err(test, "internal error occurred during test case cleanup: %d\n",
+				  try_exit_code);
+		}
+		return;
+	}
+
+	kunit_err(test, "test aborted during cleanup. continuing without cleaning up\n");
+}
+
+
 static void kunit_catch_run_case(void *data)
 {
 	struct kunit_try_catch_context *ctx = data;
@@ -448,12 +488,6 @@ static void kunit_catch_run_case(void *data)
 		}
 		return;
 	}
-
-	/*
-	 * Test case was run, but aborted. It is the test case's business as to
-	 * whether it failed or not, we just need to clean up.
-	 */
-	kunit_run_case_cleanup(test, suite);
 }
 
 /*
@@ -478,6 +512,13 @@ static void kunit_run_case_catch_errors(struct kunit_suite *suite,
 	context.test_case = test_case;
 	kunit_try_catch_run(try_catch, &context);
 
+	/* Now run the cleanup */
+	kunit_try_catch_init(try_catch,
+			     test,
+			     kunit_try_run_case_cleanup,
+			     kunit_catch_run_case_cleanup);
+	kunit_try_catch_run(try_catch, &context);
+
 	/* Propagate the parameter result to the test case. */
 	if (test->status == KUNIT_FAILURE)
 		test_case->status = KUNIT_FAILURE;
-- 
2.40.0.634.g4ca3ef3211-goog