runtime verifier updates for v7.4:

- Improve lockdep annotation for reactors
 
   Reactors are not supposed to take locks, so they fit the LD_WAIT_FREE
   lockdep class. However, reactors may run in preemptible context and
   if the preempting code (tick or simply the scheduler) takes locks, we
   see a lockdep splat. Switch to LD_WAIT_SPIN to avoid the splat while
   documenting that reactors should still not take locks.
 
 - Add KUnit tests for reactors
 
   Add KUnit test cases to validate registration and reaction, this
   requires exporting some symbols and other minor fixes.
 
 - Use the right rv_this variable in the wakeup monitor
 
   LTL monitors were updated to use the generic rv_this static variable
   but this change wasn't propagated to the newly introduced wakeup
   monitor. This broke reactors for the monitor: update the it.
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Merge tag 'trace-rv-v7.4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull runtime verifier updates from Steven Rostedt:

 - Improve lockdep annotation for reactors

   Reactors are not supposed to take locks, so they fit the LD_WAIT_FREE
   lockdep class. However, reactors may run in preemptible context and
   if the preempting code (tick or simply the scheduler) takes locks, we
   see a lockdep splat. Switch to LD_WAIT_SPIN to avoid the splat while
   documenting that reactors should still not take locks.

 - Add KUnit tests for reactors

   Add KUnit test cases to validate registration and reaction, this
   requires exporting some symbols and other minor fixes.

 - Use the right rv_this variable in the wakeup monitor

   LTL monitors were updated to use the generic rv_this static variable
   but this change wasn't propagated to the newly introduced wakeup
   monitor. This broke reactors for the monitor: update the it.

* tag 'trace-rv-v7.4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  rv/rtapp/wakeup: Use "rv_this" the rv_monitor variable
  rv: Add KUnit tests for reactor registration and dispatch
  rv: Export rv_register_reactor() and rv_unregister_reactor()
  rv: Propagate rv_register_reactor() error from reactor init
  rv: Use LD_WAIT_SPIN as the reactor lockdep wait type

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/monitors/wakeup/wakeup.c

@@ -128,7 +128,7 @@ static void disable_wakeup(void)
 	ltl_monitor_destroy();
 }
 
-static struct rv_monitor rv_wakeup = {
+static struct rv_monitor rv_this = {
 	.name = "wakeup",
 	.description = "Monitor that real-time tasks are not woken by lower-priority tasks",
 	.enable = enable_wakeup,
@@ -137,12 +137,12 @@ static struct rv_monitor rv_wakeup = {
 
 static int __init register_wakeup(void)
 {
-	return rv_register_monitor(&rv_wakeup, &rv_rtapp);
+	return rv_register_monitor(&rv_this, &rv_rtapp);
 }
 
 static void __exit unregister_wakeup(void)
 {
-	rv_unregister_monitor(&rv_wakeup);
+	rv_unregister_monitor(&rv_this);
 }
 
 module_init(register_wakeup);

kernel/trace/rv/reactor_panic.c

@@ -26,8 +26,7 @@ static struct rv_reactor rv_panic = {
 
 static int __init register_react_panic(void)
 {
-	rv_register_reactor(&rv_panic);
-	return 0;
+	return rv_register_reactor(&rv_panic);
 }
 
 static void __exit unregister_react_panic(void)

kernel/trace/rv/reactor_printk.c

@@ -25,8 +25,7 @@ static struct rv_reactor rv_printk = {
 
 static int __init register_react_printk(void)
 {
-	rv_register_reactor(&rv_printk);
-	return 0;
+	return rv_register_reactor(&rv_printk);
 }
 
 static void __exit unregister_react_printk(void)

kernel/trace/rv/rv_reactors.c

@@ -314,6 +314,7 @@ int rv_register_reactor(struct rv_reactor *reactor)
 	guard(mutex)(&rv_interface_lock);
 	return __rv_register_reactor(reactor);
 }
+EXPORT_SYMBOL_GPL(rv_register_reactor);
 
 /**
  * rv_unregister_reactor - unregister a rv reactor.
@@ -327,6 +328,7 @@ int rv_unregister_reactor(struct rv_reactor *reactor)
 	list_del(&reactor->list);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(rv_unregister_reactor);
 
 /*
  * reacting_on interface.
@@ -465,7 +467,15 @@ int init_rv_reactors(struct dentry *root_dir)
 
 void rv_react(struct rv_monitor *monitor, const char *msg, ...)
 {
-	static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_FREE);
+	/*
+	 * Reactors must not explicitly take locks, so they should be
+	 * LD_WAIT_FREE.  However, reactor callbacks can run with preemption
+	 * enabled, meaning the preempting code (e.g. the scheduler taking
+	 * rq->__lock at LD_WAIT_SPIN) may violate that constraint.  Use
+	 * LD_WAIT_SPIN to avoid false-positive lockdep reports.
+	 * But you should still NOT be using locks in reactors.
+	 */
+	static DEFINE_WAIT_OVERRIDE_MAP(rv_react_map, LD_WAIT_SPIN);
 	va_list args;
 
 	if (!rv_reacting_on() || !monitor->react)

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");