rv: Add KUnit tests for reactor registration and dispatch

Add KUnit tests covering the reactor register/unregister lifecycle
(including duplicate and name-length rejection) and rv_react() dispatch
(a no-op without a callback, exactly one invocation with one).  The
mdelay() callback keeps the CPU busy so a timer interrupt lands inside
rv_react()'s lockdep context, exercising the LD_WAIT_SPIN wait type
from the previous patch; a spurious lockdep splat there would show up
in the test output.

The dispatch tests rely on reacting_on being enabled, since rv_react()
returns early when it is off.

Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Wen Yang <wen.yang@linux.dev>
Link: https://lore.kernel.org/r/7d213b110815da45595ad8cd7bcce5641fac3404.1789412799.git.wen.yang@linux.dev
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>

kernel/trace/rv/Kconfig

@@ -113,6 +113,18 @@ config RV_REACT_PANIC
 	  Enables the panic reactor. The panic reactor emits a printk()
 	  message if an exception is found and panic()s the system.
 
+config RV_REACTORS_KUNIT
+	tristate "KUnit tests for RV reactors" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	depends on RV_REACTORS
+	default KUNIT_ALL_TESTS
+	help
+	  Enable KUnit tests for RV reactor registration and dispatch.
+	  These tests verify the register/unregister lifecycle, duplicate
+	  rejection, and that rv_react() correctly invokes callbacks.
+
+	  If unsure, say N.
+
 config RV_MONITORS_KUNIT_TEST
 	tristate "KUnit tests for RV monitors" if !KUNIT_ALL_TESTS
 	depends on KUNIT && RV && RV_REACTORS

kernel/trace/rv/Makefile

@@ -25,4 +25,5 @@ obj-$(CONFIG_RV_MON_WAKEUP) += monitors/wakeup/wakeup.o
 obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
 obj-$(CONFIG_RV_REACT_PANIC) += reactor_panic.o
+obj-$(CONFIG_RV_REACTORS_KUNIT) += rv_reactors_kunit.o
 obj-$(CONFIG_RV_MONITORS_KUNIT_TEST) += rv_monitors_test.o

kernel/trace/rv/rv_reactors_kunit.c

@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for RV reactor registration and dispatch.
+ *
+ * The dispatch tests rely on reacting_on being enabled, since rv_react()
+ * returns early when it is off. It is on by default when the suites run
+ * built-in; as a module, re-enable it if disabled via
+ * /sys/kernel/tracing/rv/reacting_on.
+ */
+
+#include <kunit/test.h>
+#include <linux/build_bug.h>
+#include <linux/rv.h>
+#include <linux/delay.h>
+#include "rv.h"
+
+static struct rv_reactor test_reactor = {
+	.name		= "kunit_test_reactor",
+	.description	= "KUnit test reactor",
+};
+
+static void reactor_teardown(void *arg)
+{
+	rv_unregister_reactor(&test_reactor);
+}
+
+static void register_test_reactor(struct kunit *test)
+{
+	KUNIT_ASSERT_EQ(test, rv_register_reactor(&test_reactor), 0);
+	KUNIT_ASSERT_EQ(test,
+			kunit_add_action_or_reset(test, reactor_teardown, NULL), 0);
+}
+
+static void test_double_register(struct kunit *test)
+{
+	register_test_reactor(test);
+	KUNIT_EXPECT_EQ(test, rv_register_reactor(&test_reactor), -EINVAL);
+}
+
+static const char long_reactor_name[] = "kunit_reactor_name_too_long_xxx_";
+static_assert(sizeof(long_reactor_name) - 1 >= MAX_RV_REACTOR_NAME_SIZE,
+	       "long_reactor_name must be at least MAX_RV_REACTOR_NAME_SIZE chars");
+
+static void test_name_too_long(struct kunit *test)
+{
+	static struct rv_reactor long_reactor = {
+		.name = long_reactor_name,
+	};
+
+	KUNIT_EXPECT_EQ(test, rv_register_reactor(&long_reactor), -EINVAL);
+}
+
+static struct kunit_case rv_reactor_registration_cases[] = {
+	KUNIT_CASE(test_double_register),
+	KUNIT_CASE(test_name_too_long),
+	{}
+};
+
+static struct kunit_suite rv_reactor_registration_suite = {
+	.name		= "rv_reactor_registration",
+	.test_cases	= rv_reactor_registration_cases,
+};
+
+static int react_call_count;
+
+__printf(1, 0) static void mock_react(const char *msg, va_list args)
+{
+	react_call_count++;
+	/* Busy-wait so a timer interrupt fires inside rv_react(). */
+	mdelay(20);
+}
+
+static void test_react_no_callback(struct kunit *test)
+{
+	struct rv_monitor monitor = {
+		.name = "kunit_null_react",
+	};
+
+	react_call_count = 0;
+	rv_react(&monitor, "no callback");
+
+	KUNIT_EXPECT_EQ(test, react_call_count, 0);
+}
+
+static void test_react_callback_invoked(struct kunit *test)
+{
+	struct rv_monitor monitor = {
+		.name	= "kunit_dispatch_monitor",
+		.react	= mock_react,
+	};
+
+	react_call_count = 0;
+	rv_react(&monitor, "callback invocation test");
+	KUNIT_EXPECT_EQ(test, react_call_count, 1);
+}
+
+static struct kunit_case rv_react_dispatch_cases[] = {
+	KUNIT_CASE(test_react_no_callback),
+	KUNIT_CASE(test_react_callback_invoked),
+	{}
+};
+
+static struct kunit_suite rv_react_dispatch_suite = {
+	.name		= "rv_react_dispatch",
+	.test_cases	= rv_react_dispatch_cases,
+};
+
+kunit_test_suites(&rv_reactor_registration_suite, &rv_react_dispatch_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit tests for RV reactor registration and dispatch");