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, 219 insertions, 0 deletions

diff --git a/drivers/leds/uleds.c b/drivers/leds/uleds.c
new file mode 100644
index 000000000..6affa581b
--- /dev/null
+++ b/drivers/leds/uleds.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Userspace driver for the LED subsystem
+ *
+ * Copyright (C) 2016 David Lechner <david@lechnology.com>
+ *
+ * Based on uinput.c: Aristeu Sergio Rozanski Filho <aris@cathedrallabs.org>
+ */
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/leds.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+
+#include <uapi/linux/uleds.h>
+
+#define ULEDS_NAME	"uleds"
+
+enum uleds_state {
+	ULEDS_STATE_UNKNOWN,
+	ULEDS_STATE_REGISTERED,
+};
+
+struct uleds_device {
+	struct uleds_user_dev	user_dev;
+	struct led_classdev	led_cdev;
+	struct mutex		mutex;
+	enum uleds_state	state;
+	wait_queue_head_t	waitq;
+	int			brightness;
+	bool			new_data;
+};
+
+static struct miscdevice uleds_misc;
+
+static void uleds_brightness_set(struct led_classdev *led_cdev,
+				 enum led_brightness brightness)
+{
+	struct uleds_device *udev = container_of(led_cdev, struct uleds_device,
+						 led_cdev);
+
+	if (udev->brightness != brightness) {
+		udev->brightness = brightness;
+		udev->new_data = true;
+		wake_up_interruptible(&udev->waitq);
+	}
+}
+
+static int uleds_open(struct inode *inode, struct file *file)
+{
+	struct uleds_device *udev;
+
+	udev = kzalloc_obj(*udev);
+	if (!udev)
+		return -ENOMEM;
+
+	udev->led_cdev.name = udev->user_dev.name;
+	udev->led_cdev.brightness_set = uleds_brightness_set;
+
+	mutex_init(&udev->mutex);
+	init_waitqueue_head(&udev->waitq);
+	udev->state = ULEDS_STATE_UNKNOWN;
+
+	file->private_data = udev;
+	stream_open(inode, file);
+
+	return 0;
+}
+
+static ssize_t uleds_write(struct file *file, const char __user *buffer,
+			   size_t count, loff_t *ppos)
+{
+	struct uleds_device *udev = file->private_data;
+	const char *name;
+	int ret;
+
+	if (count == 0)
+		return 0;
+
+	ret = mutex_lock_interruptible(&udev->mutex);
+	if (ret)
+		return ret;
+
+	if (udev->state == ULEDS_STATE_REGISTERED) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	if (count != sizeof(struct uleds_user_dev)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (copy_from_user(&udev->user_dev, buffer,
+			   sizeof(struct uleds_user_dev))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	name = udev->user_dev.name;
+	if (!name[0] || !strcmp(name, ".") || !strcmp(name, "..") ||
+	    strnchr(name, sizeof(udev->user_dev.name), '/') ||
+	    !strnchr(name, sizeof(udev->user_dev.name), '\0')) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (udev->user_dev.max_brightness <= 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+	udev->led_cdev.max_brightness = udev->user_dev.max_brightness;
+
+	ret = devm_led_classdev_register(uleds_misc.this_device,
+					 &udev->led_cdev);
+	if (ret < 0)
+		goto out;
+
+	udev->new_data = true;
+	udev->state = ULEDS_STATE_REGISTERED;
+	ret = count;
+
+out:
+	mutex_unlock(&udev->mutex);
+
+	return ret;
+}
+
+static ssize_t uleds_read(struct file *file, char __user *buffer, size_t count,
+			  loff_t *ppos)
+{
+	struct uleds_device *udev = file->private_data;
+	ssize_t retval;
+
+	if (count < sizeof(udev->brightness))
+		return 0;
+
+	do {
+		retval = mutex_lock_interruptible(&udev->mutex);
+		if (retval)
+			return retval;
+
+		if (udev->state != ULEDS_STATE_REGISTERED) {
+			retval = -ENODEV;
+		} else if (!udev->new_data && (file->f_flags & O_NONBLOCK)) {
+			retval = -EAGAIN;
+		} else if (udev->new_data) {
+			if (copy_to_user(buffer, &udev->brightness,
+					 sizeof(udev->brightness))) {
+				retval = -EFAULT;
+			} else {
+				udev->new_data = false;
+				retval = sizeof(udev->brightness);
+			}
+		}
+
+		mutex_unlock(&udev->mutex);
+
+		if (retval)
+			break;
+
+		if (!(file->f_flags & O_NONBLOCK))
+			retval = wait_event_interruptible(udev->waitq,
+					udev->new_data ||
+					udev->state != ULEDS_STATE_REGISTERED);
+	} while (retval == 0);
+
+	return retval;
+}
+
+static __poll_t uleds_poll(struct file *file, poll_table *wait)
+{
+	struct uleds_device *udev = file->private_data;
+
+	poll_wait(file, &udev->waitq, wait);
+
+	if (udev->new_data)
+		return EPOLLIN | EPOLLRDNORM;
+
+	return 0;
+}
+
+static int uleds_release(struct inode *inode, struct file *file)
+{
+	struct uleds_device *udev = file->private_data;
+
+	if (udev->state == ULEDS_STATE_REGISTERED) {
+		udev->state = ULEDS_STATE_UNKNOWN;
+		devm_led_classdev_unregister(uleds_misc.this_device,
+					     &udev->led_cdev);
+	}
+	kfree(udev);
+
+	return 0;
+}
+
+static const struct file_operations uleds_fops = {
+	.owner		= THIS_MODULE,
+	.open		= uleds_open,
+	.release	= uleds_release,
+	.read		= uleds_read,
+	.write		= uleds_write,
+	.poll		= uleds_poll,
+};
+
+static struct miscdevice uleds_misc = {
+	.fops		= &uleds_fops,
+	.minor		= MISC_DYNAMIC_MINOR,
+	.name		= ULEDS_NAME,
+};
+
+module_misc_device(uleds_misc);
+
+MODULE_AUTHOR("David Lechner <david@lechnology.com>");
+MODULE_DESCRIPTION("Userspace driver for the LED subsystem");
+MODULE_LICENSE("GPL");