gpiolib: replace the GPIO device mutex with a read-write semaphore

There are only two spots where we modify (add to or remove objects from)
the GPIO device list. Readers should be able to access it concurrently.
Replace the mutex with a read-write semaphore and adjust the locking
operations accordingly.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 2d29ae37d953d28e27ff8dace992bc0cf6913656..4dbf298bb5dda0f3fadc58843707d593a1adbc5c 100644 (file)
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -773,7 +773,7 @@ int gpiochip_sysfs_register_all(void)
        struct gpio_device *gdev;
        int ret;
 
-       guard(mutex)(&gpio_devices_lock);
+       guard(rwsem_read)(&gpio_devices_sem);
 
        list_for_each_entry(gdev, &gpio_devices, list) {
                if (gdev->mockdev)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e019c4243809bbcb11ac88dea131484026d7b94b..4c93cf73a8260569de5287a4b2ae231dc54dbab6 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -85,7 +85,7 @@ static DEFINE_MUTEX(gpio_lookup_lock);
 static LIST_HEAD(gpio_lookup_list);
 
 LIST_HEAD(gpio_devices);
-DEFINE_MUTEX(gpio_devices_lock);
+DECLARE_RWSEM(gpio_devices_sem);
 
 static DEFINE_MUTEX(gpio_machine_hogs_mutex);
 static LIST_HEAD(gpio_machine_hogs);
@@ -118,7 +118,7 @@ struct gpio_desc *gpio_to_desc(unsigned gpio)
 {
        struct gpio_device *gdev;
 
-       scoped_guard(mutex, &gpio_devices_lock) {
+       scoped_guard(rwsem_read, &gpio_devices_sem) {
                list_for_each_entry(gdev, &gpio_devices, list) {
                        if (gdev->base <= gpio &&
                            gdev->base + gdev->ngpio > gpio)
@@ -402,7 +402,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
        if (!name)
                return NULL;
 
-       guard(mutex)(&gpio_devices_lock);
+       guard(rwsem_read)(&gpio_devices_sem);
 
        list_for_each_entry(gdev, &gpio_devices, list) {
                struct gpio_desc *desc;
@@ -871,7 +871,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
        gdev->ngpio = gc->ngpio;
 
-       scoped_guard(mutex, &gpio_devices_lock) {
+       scoped_guard(rwsem_write, &gpio_devices_sem) {
                /*
                 * TODO: this allocates a Linux GPIO number base in the global
                 * GPIO numberspace for this chip. In the long run we want to
@@ -1001,7 +1001,7 @@ err_free_gpiochip_mask:
                goto err_print_message;
        }
 err_remove_from_list:
-       scoped_guard(mutex, &gpio_devices_lock)
+       scoped_guard(rwsem_write, &gpio_devices_sem)
                list_del(&gdev->list);
 err_free_label:
        kfree_const(gdev->label);
@@ -1065,7 +1065,7 @@ void gpiochip_remove(struct gpio_chip *gc)
                dev_crit(&gdev->dev,
                         "REMOVING GPIOCHIP WITH GPIOS STILL REQUESTED\n");
 
-       scoped_guard(mutex, &gpio_devices_lock)
+       scoped_guard(rwsem_write, &gpio_devices_sem)
                list_del(&gdev->list);
 
        /*
@@ -1114,7 +1114,7 @@ struct gpio_device *gpio_device_find(void *data,
         */
        might_sleep();
 
-       guard(mutex)(&gpio_devices_lock);
+       guard(rwsem_read)(&gpio_devices_sem);
 
        list_for_each_entry(gdev, &gpio_devices, list) {
                if (gdev->chip && match(gdev->chip, data))
@@ -4730,7 +4730,7 @@ static void *gpiolib_seq_start(struct seq_file *s, loff_t *pos)
 
        s->private = "";
 
-       guard(mutex)(&gpio_devices_lock);
+       guard(rwsem_read)(&gpio_devices_sem);
 
        list_for_each_entry(gdev, &gpio_devices, list) {
                if (index-- == 0)
@@ -4745,7 +4745,7 @@ static void *gpiolib_seq_next(struct seq_file *s, void *v, loff_t *pos)
        struct gpio_device *gdev = v;
        void *ret = NULL;
 
-       scoped_guard(mutex, &gpio_devices_lock) {
+       scoped_guard(rwsem_read, &gpio_devices_sem) {
                if (list_is_last(&gdev->list, &gpio_devices))
                        ret = NULL;
                else

diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 0ce7451a6b24a4269c18124818177b168ba1e7d7..97df54abf57ac0f2a740d72bf37965b299d87927 100644 (file)
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -137,7 +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;
+extern struct rw_semaphore gpio_devices_sem;
 
 void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action);