gpiolib: use a mutex to protect the list of GPIO devices

The global list of GPIO devices is never modified or accessed from
atomic context so it's fine to protect it using a mutex. Add a new
global lock dedicated to the gpio_devices list and use it whenever
accessing or modifying it.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpiolib-sysfs.c

@@ -766,6 +766,25 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
 	return 0;
 }
 
+int gpiochip_sysfs_register_all(void)
+{
+	struct gpio_device *gdev;
+	int ret;
+
+	guard(mutex)(&gpio_devices_lock);
+
+	list_for_each_entry(gdev, &gpio_devices, list) {
+		if (gdev->mockdev)
+			continue;
+
+		ret = gpiochip_sysfs_register(gdev);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 {
 	struct gpio_desc *desc;
@@ -791,8 +810,6 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 static int __init gpiolib_sysfs_init(void)
 {
 	int status;
-	unsigned long	flags;
-	struct gpio_device *gdev;
 
 	status = class_register(&gpio_class);
 	if (status < 0)
@@ -804,26 +821,6 @@ static int __init gpiolib_sysfs_init(void)
 	 * We run before arch_initcall() so chip->dev nodes can have
 	 * registered, and so arch_initcall() can always gpiod_export().
 	 */
-	spin_lock_irqsave(&gpio_lock, flags);
-	list_for_each_entry(gdev, &gpio_devices, list) {
-		if (gdev->mockdev)
-			continue;
-
-		/*
-		 * TODO we yield gpio_lock here because
-		 * gpiochip_sysfs_register() acquires a mutex. This is unsafe
-		 * and needs to be fixed.
-		 *
-		 * Also it would be nice to use gpio_device_find() here so we
-		 * can keep gpio_chips local to gpiolib.c, but the yield of
-		 * gpio_lock prevents us from doing this.
-		 */
-		spin_unlock_irqrestore(&gpio_lock, flags);
-		status = gpiochip_sysfs_register(gdev);
-		spin_lock_irqsave(&gpio_lock, flags);
-	}
-	spin_unlock_irqrestore(&gpio_lock, flags);
-
-	return status;
+	return gpiochip_sysfs_register_all();
 }
 postcore_initcall(gpiolib_sysfs_init);

drivers/gpio/gpiolib-sysfs.h

@@ -8,6 +8,7 @@ struct gpio_device;
 #ifdef CONFIG_GPIO_SYSFS
 
 int gpiochip_sysfs_register(struct gpio_device *gdev);
+int gpiochip_sysfs_register_all(void);
 void gpiochip_sysfs_unregister(struct gpio_device *gdev);
 
 #else
@@ -17,6 +18,11 @@ static inline int gpiochip_sysfs_register(struct gpio_device *gdev)
 	return 0;
 }
 
+static inline int gpiochip_sysfs_register_all(void)
+{
+	return 0;
+}
+
 static inline void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 {
 }

drivers/gpio/gpiolib.c

@@ -2,6 +2,7 @@
 
 #include <linux/acpi.h>
 #include <linux/bitmap.h>
+#include <linux/cleanup.h>
 #include <linux/compat.h>
 #include <linux/debugfs.h>
 #include <linux/device.h>
@@ -15,6 +16,7 @@
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/seq_file.h>
@@ -94,7 +96,9 @@ DEFINE_SPINLOCK(gpio_lock);
 
 static DEFINE_MUTEX(gpio_lookup_lock);
 static LIST_HEAD(gpio_lookup_list);
+
 LIST_HEAD(gpio_devices);
+DEFINE_MUTEX(gpio_devices_lock);
 
 static DEFINE_MUTEX(gpio_machine_hogs_mutex);
 static LIST_HEAD(gpio_machine_hogs);
@@ -126,20 +130,15 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label)
 struct gpio_desc *gpio_to_desc(unsigned gpio)
 {
 	struct gpio_device *gdev;
-	unsigned long flags;
-
-	spin_lock_irqsave(&gpio_lock, flags);
 
+	scoped_guard(mutex, &gpio_devices_lock) {
 		list_for_each_entry(gdev, &gpio_devices, list) {
 			if (gdev->base <= gpio &&
-		    gdev->base + gdev->ngpio > gpio) {
-			spin_unlock_irqrestore(&gpio_lock, flags);
+			    gdev->base + gdev->ngpio > gpio)
 				return &gdev->descs[gpio - gdev->base];
 		}
 	}
 
-	spin_unlock_irqrestore(&gpio_lock, flags);
-
 	if (!gpio_is_valid(gpio))
 		pr_warn("invalid GPIO %d\n", gpio);
 
@@ -412,25 +411,20 @@ static int gpiodev_add_to_list_unlocked(struct gpio_device *gdev)
 static struct gpio_desc *gpio_name_to_desc(const char * const name)
 {
 	struct gpio_device *gdev;
-	unsigned long flags;
 
 	if (!name)
 		return NULL;
 
-	spin_lock_irqsave(&gpio_lock, flags);
+	guard(mutex)(&gpio_devices_lock);
 
 	list_for_each_entry(gdev, &gpio_devices, list) {
 		struct gpio_desc *desc;
 
 		for_each_gpio_desc(gdev->chip, desc) {
-			if (desc->name && !strcmp(desc->name, name)) {
-				spin_unlock_irqrestore(&gpio_lock, flags);
+			if (desc->name && !strcmp(desc->name, name))
 				return desc;
 		}
 	}
-	}
-
-	spin_unlock_irqrestore(&gpio_lock, flags);
 
 	return NULL;
 }
@@ -669,11 +663,9 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
 static void gpiodev_release(struct device *dev)
 {
 	struct gpio_device *gdev = to_gpio_device(dev);
-	unsigned long flags;
 
-	spin_lock_irqsave(&gpio_lock, flags);
+	scoped_guard(mutex, &gpio_devices_lock)
 		list_del(&gdev->list);
-	spin_unlock_irqrestore(&gpio_lock, flags);
 
 	ida_free(&gpio_ida, gdev->id);
 	kfree_const(gdev->label);
@@ -831,7 +823,6 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			       struct lock_class_key *request_key)
 {
 	struct gpio_device *gdev;
-	unsigned long flags;
 	unsigned int i;
 	int base = 0;
 	int ret = 0;
@@ -896,8 +887,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
 	gdev->ngpio = gc->ngpio;
 
-	spin_lock_irqsave(&gpio_lock, flags);
-
+	scoped_guard(mutex, &gpio_devices_lock) {
 		/*
 		 * TODO: this allocates a Linux GPIO number base in the global
 		 * GPIO numberspace for this chip. In the long run we want to
@@ -906,10 +896,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		 * of the sysfs interface anyways.
 		 */
 		base = gc->base;
+
 		if (base < 0) {
 			base = gpiochip_find_base_unlocked(gc->ngpio);
 			if (base < 0) {
-			spin_unlock_irqrestore(&gpio_lock, flags);
 				ret = base;
 				base = 0;
 				goto err_free_label;
@@ -929,15 +919,13 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
 		ret = gpiodev_add_to_list_unlocked(gdev);
 		if (ret) {
-		spin_unlock_irqrestore(&gpio_lock, flags);
 			chip_err(gc, "GPIO integer space overlap, cannot add chip\n");
 			goto err_free_label;
 		}
 
 		for (i = 0; i < gc->ngpio; i++)
 			gdev->descs[i].gdev = gdev;
-
-	spin_unlock_irqrestore(&gpio_lock, flags);
+	}
 
 	BLOCKING_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
 	BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
@@ -1029,9 +1017,8 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		goto err_print_message;
 	}
 err_remove_from_list:
-	spin_lock_irqsave(&gpio_lock, flags);
+	scoped_guard(mutex, &gpio_devices_lock)
 		list_del(&gdev->list);
-	spin_unlock_irqrestore(&gpio_lock, flags);
 err_free_label:
 	kfree_const(gdev->label);
 err_free_descs:
@@ -1140,7 +1127,7 @@ struct gpio_device *gpio_device_find(void *data,
 	 */
 	might_sleep();
 
-	guard(spinlock_irqsave)(&gpio_lock);
+	guard(mutex)(&gpio_devices_lock);
 
 	list_for_each_entry(gdev, &gpio_devices, list) {
 		if (gdev->chip && match(gdev->chip, data))
@@ -4756,35 +4743,33 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
 
 static void *gpiolib_seq_start(struct seq_file *s, loff_t *pos)
 {
-	unsigned long flags;
 	struct gpio_device *gdev = NULL;
 	loff_t index = *pos;
 
 	s->private = "";
 
-	spin_lock_irqsave(&gpio_lock, flags);
-	list_for_each_entry(gdev, &gpio_devices, list)
-		if (index-- == 0) {
-			spin_unlock_irqrestore(&gpio_lock, flags);
+	guard(mutex)(&gpio_devices_lock);
+
+	list_for_each_entry(gdev, &gpio_devices, list) {
+		if (index-- == 0)
 			return gdev;
 	}
-	spin_unlock_irqrestore(&gpio_lock, flags);
 
 	return NULL;
 }
 
 static void *gpiolib_seq_next(struct seq_file *s, void *v, loff_t *pos)
 {
-	unsigned long flags;
 	struct gpio_device *gdev = v;
 	void *ret = NULL;
 
-	spin_lock_irqsave(&gpio_lock, flags);
+	scoped_guard(mutex, &gpio_devices_lock) {
 		if (list_is_last(&gdev->list, &gpio_devices))
 			ret = NULL;
 		else
-		ret = list_first_entry(&gdev->list, struct gpio_device, list);
-	spin_unlock_irqrestore(&gpio_lock, flags);
+			ret = list_first_entry(&gdev->list, struct gpio_device,
+					       list);
+	}
 
 	s->private = "\n";
 	++*pos;

drivers/gpio/gpiolib.h

@@ -15,6 +15,7 @@
 #include <linux/gpio/consumer.h> /* for enum gpiod_flags */
 #include <linux/gpio/driver.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/notifier.h>
 #include <linux/rwsem.h>
 
@@ -136,6 +137,7 @@ int gpiod_set_transitory(struct gpio_desc *desc, bool transitory);
 
 extern spinlock_t gpio_lock;
 extern struct list_head gpio_devices;
+extern struct mutex gpio_devices_lock;
 
 void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action);