[PATCH 3/3] rv/reactors: add KUnit tests for reactor_panic

[wen.yang@linux.dev]

From: Wen Yang <wen.yang@linux.dev>

Add KUnit tests for the panic reactor covering:
- Reactor registration and unregistration lifecycle
- Panic notifier chain reachability

The real rv_panic_reaction() calls vpanic(), which is __noreturn and
halts the system. KUnit cannot test across that boundary. Instead, the
test drives atomic_notifier_call_chain(&panic_notifier_list, ...) directly
with a high-priority mock notifier that returns NOTIFY_STOP, verifying
that the panic notification propagates without triggering real handlers
(kdump, watchdog, reboot).

The mock notifier busy-waits to simulate real handler execution time
(e.g., crash_save_vmcoreinfo, emergency_restart preamble) under the
panic context constraints.

Signed-off-by: Wen Yang <wen.yang@linux.dev>
---
 kernel/trace/rv/Kconfig               |  10 +++
 kernel/trace/rv/Makefile              |   1 +
 kernel/trace/rv/reactor_panic_kunit.c | 106 ++++++++++++++++++++++++++
 3 files changed, 117 insertions(+)
 create mode 100644 kernel/trace/rv/reactor_panic_kunit.c

diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index ff47895c897f..6c6c43c5f86c 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -121,3 +121,13 @@ config RV_REACT_PANIC
 	help
 	  Enables the panic reactor. The panic reactor emits a printk()
 	  message if an exception is found and panic()s the system.
+
+config RV_REACT_PANIC_KUNIT
+	bool "KUnit tests for reactor_panic" if !KUNIT_ALL_TESTS
+	depends on RV_REACT_PANIC && KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds KUnit tests for the panic reactor. These are only
+	  for development and testing, not for regular kernel use cases.
+
+	  If unsure, say N.
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index ef0a2dcb927c..2ebfe5e5068c 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -25,3 +25,4 @@ obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
 obj-$(CONFIG_RV_REACT_PRINTK_KUNIT) += reactor_printk_kunit.o
 obj-$(CONFIG_RV_REACT_PANIC) += reactor_panic.o
+obj-$(CONFIG_RV_REACT_PANIC_KUNIT) += reactor_panic_kunit.o
diff --git a/kernel/trace/rv/reactor_panic_kunit.c b/kernel/trace/rv/reactor_panic_kunit.c
new file mode 100644
index 000000000000..f9a09ae7aaad
--- /dev/null
+++ b/kernel/trace/rv/reactor_panic_kunit.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for reactor_panic
+ *
+ */
+
+#include <kunit/test.h>
+#include <linux/rv.h>
+#include <linux/panic_notifier.h>
+#include <linux/notifier.h>
+#include <linux/limits.h>
+#include <linux/sched/clock.h>
+#include <linux/processor.h>
+
+/* Simulated execution time for mock panic notifier (nanoseconds). */
+#define RV_PANIC_NOTIFIER_EXEC_NS	2000000ULL
+
+/* Test state */
+static struct {
+	bool notifier_called;
+} panic_test_state;
+
+/*
+ * Mock panic notifier callback.
+ *
+ * Runs at INT_MAX priority and returns NOTIFY_STOP to prevent real panic
+ * handlers (kdump, watchdog) from executing during the test.  Busy-waits
+ * RV_PANIC_NOTIFIER_EXEC_NS to simulate a real handler's execution time.
+ */
+static int mock_panic_notifier_fn(struct notifier_block *nb,
+				  unsigned long action, void *data)
+{
+	char *msg = data;
+	u64 start = sched_clock();
+
+	panic_test_state.notifier_called = true;
+	pr_emerg("KUnit: reactor_panic test intercepted panic notifier: %s\n",
+		 msg ? msg : "(no message)");
+
+	while (sched_clock() - start < RV_PANIC_NOTIFIER_EXEC_NS)
+		cpu_relax();
+
+	return NOTIFY_STOP;
+}
+
+static struct notifier_block mock_panic_nb = {
+	.notifier_call	= mock_panic_notifier_fn,
+	.priority	= INT_MAX,
+};
+
+static struct rv_reactor mock_panic_reactor = {
+	.name		= "test_panic",
+	.description	= "test panic reactor",
+};
+
+static int reactor_panic_kunit_init(struct kunit *test)
+{
+	panic_test_state.notifier_called = false;
+	return 0;
+}
+
+/* Test 1: register and unregister reactor */
+static void test_panic_register_unregister(struct kunit *test)
+{
+	int ret;
+
+	ret = rv_register_reactor(&mock_panic_reactor);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_STREQ(test, mock_panic_reactor.name, "test_panic");
+
+	rv_unregister_reactor(&mock_panic_reactor);
+}
+
+/*
+ * Test 2: panic notifier chain is reachable.
+ *
+ * vpanic() calls atomic_notifier_call_chain(&panic_notifier_list, ...).
+ * Drive the chain directly to verify panic notifiers receive the notification —
+ * the observable side-effect of reactor_panic without halting the system.
+ */
+static void test_panic_notifier_called(struct kunit *test)
+{
+	atomic_notifier_chain_register(&panic_notifier_list, &mock_panic_nb);
+	atomic_notifier_call_chain(&panic_notifier_list, 0,
+				   "panic violation message");
+	atomic_notifier_chain_unregister(&panic_notifier_list, &mock_panic_nb);
+
+	KUNIT_EXPECT_TRUE(test, panic_test_state.notifier_called);
+}
+
+static struct kunit_case reactor_panic_kunit_cases[] = {
+	KUNIT_CASE(test_panic_register_unregister),
+	KUNIT_CASE(test_panic_notifier_called),
+	{}
+};
+
+static struct kunit_suite reactor_panic_kunit_suite = {
+	.name		= "rv_reactor_panic",
+	.init		= reactor_panic_kunit_init,
+	.test_cases	= reactor_panic_kunit_cases,
+};
+
+kunit_test_suite(reactor_panic_kunit_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit tests for reactor_panic");
-- 
2.25.1