ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 112 insertions, 0 deletions

diff --git a/drivers/base/test/root-device-test.c b/drivers/base/test/root-device-test.c
new file mode 100644
index 000000000..9aea23c91
--- /dev/null
+++ b/drivers/base/test/root-device-test.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright 2023 Maxime Ripard <mripard@kernel.org>
+
+#include <kunit/resource.h>
+
+#include <linux/device.h>
+
+#define DEVICE_NAME "test"
+
+struct test_priv {
+	bool probe_done;
+	bool release_done;
+	wait_queue_head_t release_wq;
+	struct device *dev;
+};
+
+static int root_device_devm_init(struct kunit *test)
+{
+	struct test_priv *priv;
+
+	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv);
+	init_waitqueue_head(&priv->release_wq);
+
+	test->priv = priv;
+
+	return 0;
+}
+
+static void devm_device_action(void *ptr)
+{
+	struct test_priv *priv = ptr;
+
+	priv->release_done = true;
+	wake_up_interruptible(&priv->release_wq);
+}
+
+#define RELEASE_TIMEOUT_MS	100
+
+/*
+ * Tests that a bus-less, non-probed device will run its device-managed
+ * actions when unregistered.
+ */
+static void root_device_devm_register_unregister_test(struct kunit *test)
+{
+	struct test_priv *priv = test->priv;
+	int ret;
+
+	priv->dev = root_device_register(DEVICE_NAME);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv->dev);
+
+	ret = devm_add_action_or_reset(priv->dev, devm_device_action, priv);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	root_device_unregister(priv->dev);
+
+	ret = wait_event_interruptible_timeout(priv->release_wq, priv->release_done,
+					       msecs_to_jiffies(RELEASE_TIMEOUT_MS));
+	KUNIT_EXPECT_GT(test, ret, 0);
+}
+
+static void devm_put_device_action(void *ptr)
+{
+	struct test_priv *priv = ptr;
+
+	put_device(priv->dev);
+	priv->release_done = true;
+	wake_up_interruptible(&priv->release_wq);
+}
+
+/*
+ * Tests that a bus-less, non-probed device will run its device-managed
+ * actions when unregistered, even if someone still holds a reference to
+ * it.
+ */
+static void root_device_devm_register_get_unregister_with_devm_test(struct kunit *test)
+{
+	struct test_priv *priv = test->priv;
+	int ret;
+
+	priv->dev = root_device_register(DEVICE_NAME);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv->dev);
+
+	get_device(priv->dev);
+
+	ret = devm_add_action_or_reset(priv->dev, devm_put_device_action, priv);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	root_device_unregister(priv->dev);
+
+	ret = wait_event_interruptible_timeout(priv->release_wq, priv->release_done,
+					       msecs_to_jiffies(RELEASE_TIMEOUT_MS));
+	KUNIT_EXPECT_GT(test, ret, 0);
+}
+
+static struct kunit_case root_device_devm_tests[] = {
+	KUNIT_CASE(root_device_devm_register_unregister_test),
+	KUNIT_CASE(root_device_devm_register_get_unregister_with_devm_test),
+	{}
+};
+
+static struct kunit_suite root_device_devm_test_suite = {
+	.name = "root-device-devm",
+	.init = root_device_devm_init,
+	.test_cases = root_device_devm_tests,
+};
+
+kunit_test_suite(root_device_devm_test_suite);
+
+MODULE_DESCRIPTION("Test module for root devices");
+MODULE_AUTHOR("Maxime Ripard <mripard@kernel.org>");
+MODULE_LICENSE("GPL");