[PATCH v4 RESEND 6/7] kunit: Print last test location on fault

["Mickaël Salaün" <mic@digikod.net>]

This helps identify the location of test faults with opportunistic calls
to _KUNIT_SAVE_LOC().  This can be useful while writing tests or
debugging them.  It is possible to call KUNIT_SUCCESS() to explicit save
last location.

Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Cc: Rae Moar <rmoar@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240408074625.65017-7-mic@digikod.net
---

Changes since v3:
* Improve the try-fault error message as suggested by David.

Changes since v2:
* Extend the commit message according to discussion with David.

Changes since v1:
* Add Kees's Reviewed-by.
---
 include/kunit/test.h  | 24 +++++++++++++++++++++---
 lib/kunit/try-catch.c | 10 +++++++---
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/include/kunit/test.h b/include/kunit/test.h
index fcb4a4940ace..f3aa66eb0087 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -301,6 +301,8 @@ struct kunit {
 	struct list_head resources; /* Protected by lock. */
 
 	char status_comment[KUNIT_STATUS_COMMENT_SIZE];
+	/* Saves the last seen test. Useful to help with faults. */
+	struct kunit_loc last_seen;
 };
 
 static inline void kunit_set_failure(struct kunit *test)
@@ -567,6 +569,15 @@ void __printf(2, 3) kunit_log_append(struct string_stream *log, const char *fmt,
 #define kunit_err(test, fmt, ...) \
 	kunit_printk(KERN_ERR, test, fmt, ##__VA_ARGS__)
 
+/*
+ * Must be called at the beginning of each KUNIT_*_ASSERTION().
+ * Cf. KUNIT_CURRENT_LOC.
+ */
+#define _KUNIT_SAVE_LOC(test) do {					       \
+	WRITE_ONCE(test->last_seen.file, __FILE__);			       \
+	WRITE_ONCE(test->last_seen.line, __LINE__);			       \
+} while (0)
+
 /**
  * KUNIT_SUCCEED() - A no-op expectation. Only exists for code clarity.
  * @test: The test context object.
@@ -575,7 +586,7 @@ void __printf(2, 3) kunit_log_append(struct string_stream *log, const char *fmt,
  * words, it does nothing and only exists for code clarity. See
  * KUNIT_EXPECT_TRUE() for more information.
  */
-#define KUNIT_SUCCEED(test) do {} while (0)
+#define KUNIT_SUCCEED(test) _KUNIT_SAVE_LOC(test)
 
 void __noreturn __kunit_abort(struct kunit *test);
 
@@ -601,14 +612,16 @@ void __kunit_do_failed_assertion(struct kunit *test,
 } while (0)
 
 
-#define KUNIT_FAIL_ASSERTION(test, assert_type, fmt, ...)		       \
+#define KUNIT_FAIL_ASSERTION(test, assert_type, fmt, ...) do {		       \
+	_KUNIT_SAVE_LOC(test);						       \
 	_KUNIT_FAILED(test,						       \
 		      assert_type,					       \
 		      kunit_fail_assert,				       \
 		      kunit_fail_assert_format,				       \
 		      {},						       \
 		      fmt,						       \
-		      ##__VA_ARGS__)
+		      ##__VA_ARGS__);					       \
+} while (0)
 
 /**
  * KUNIT_FAIL() - Always causes a test to fail when evaluated.
@@ -637,6 +650,7 @@ void __kunit_do_failed_assertion(struct kunit *test,
 			      fmt,					       \
 			      ...)					       \
 do {									       \
+	_KUNIT_SAVE_LOC(test);						       \
 	if (likely(!!(condition_) == !!expected_true_))			       \
 		break;							       \
 									       \
@@ -698,6 +712,7 @@ do {									       \
 		.right_text = #right,					       \
 	};								       \
 									       \
+	_KUNIT_SAVE_LOC(test);						       \
 	if (likely(__left op __right))					       \
 		break;							       \
 									       \
@@ -758,6 +773,7 @@ do {									       \
 		.right_text = #right,					       \
 	};								       \
 									       \
+	_KUNIT_SAVE_LOC(test);						       \
 	if (likely((__left) && (__right) && (strcmp(__left, __right) op 0)))   \
 		break;							       \
 									       \
@@ -791,6 +807,7 @@ do {									       \
 		.right_text = #right,					       \
 	};								       \
 									       \
+	_KUNIT_SAVE_LOC(test);						       \
 	if (likely(__left && __right))					       \
 		if (likely(memcmp(__left, __right, __size) op 0))	       \
 			break;						       \
@@ -815,6 +832,7 @@ do {									       \
 do {									       \
 	const typeof(ptr) __ptr = (ptr);				       \
 									       \
+	_KUNIT_SAVE_LOC(test);						       \
 	if (!IS_ERR_OR_NULL(__ptr))					       \
 		break;							       \
 									       \
diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
index 7a3910dd78a6..fa687278ccc9 100644
--- a/lib/kunit/try-catch.c
+++ b/lib/kunit/try-catch.c
@@ -96,9 +96,13 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
 
 	if (exit_code == -EFAULT)
 		try_catch->try_result = 0;
-	else if (exit_code == -EINTR)
-		kunit_err(test, "try faulted\n");
-	else if (exit_code == -ETIMEDOUT)
+	else if (exit_code == -EINTR) {
+		if (test->last_seen.file)
+			kunit_err(test, "try faulted: last line seen %s:%d\n",
+				  test->last_seen.file, test->last_seen.line);
+		else
+			kunit_err(test, "try faulted\n");
+	} else if (exit_code == -ETIMEDOUT)
 		kunit_err(test, "try timed out\n");
 	else if (exit_code)
 		kunit_err(test, "Unknown error: %d\n", exit_code);
-- 
2.44.0