kunit: Handle thread creation error

Previously, if a thread creation failed (e.g. -ENOMEM), the function was
called (kunit_catch_run_case or kunit_catch_run_case_cleanup) without
marking the test as failed.  Instead, fill try_result with the error
code returned by kthread_run(), which will mark the test as failed and
print "internal error occurred...".

Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240408074625.65017-2-mic@digikod.netSigned-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/kunit/try-catch.c

@@ -69,6 +69,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
 				  try_catch,
 				  "kunit_try_catch_thread");
 	if (IS_ERR(task_struct)) {
+		try_catch->try_result = PTR_ERR(task_struct);
 		try_catch->catch(try_catch->context);
 		return;
 	}