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a=openpgp; fpr=169DEB6C0BC3C46013D2C79F11A72EA01471D772 From: Bartosz Golaszewski Atomic notifiers call rcu_synchronize() in atomic_notifier_chain_unregister() causing a considerable delay in some circumstances. Replace the atomic notifier with the raw variant and provide synchronization with a read-write spinlock. Fixes: fcc8b637c542 ("gpiolib: switch the line state notifier to atomic") Reported-by: David Jander Closes: https://lore.kernel.org/all/20250311110034.53959031@erd003.prtnl/ Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib-cdev.c | 15 +++++++++------ drivers/gpio/gpiolib.c | 8 +++++--- drivers/gpio/gpiolib.h | 5 ++++- 3 files changed, 18 insertions(+), 10 deletions(-) --- base-commit: 0a2f889128969dab41861b6e40111aa03dc57014 change-id: 20250311-gpiolib-line-state-raw-notifier-70c1ad3e99eb Best regards, diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index 40f76a90fd7d..107d75558b5a 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -2729,8 +2729,9 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file) cdev->gdev = gpio_device_get(gdev); cdev->lineinfo_changed_nb.notifier_call = lineinfo_changed_notify; - ret = atomic_notifier_chain_register(&gdev->line_state_notifier, - &cdev->lineinfo_changed_nb); + scoped_guard(write_lock_irqsave, &gdev->line_state_lock) + ret = raw_notifier_chain_register(&gdev->line_state_notifier, + &cdev->lineinfo_changed_nb); if (ret) goto out_free_bitmap; @@ -2754,8 +2755,9 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file) blocking_notifier_chain_unregister(&gdev->device_notifier, &cdev->device_unregistered_nb); out_unregister_line_notifier: - atomic_notifier_chain_unregister(&gdev->line_state_notifier, - &cdev->lineinfo_changed_nb); + scoped_guard(write_lock_irqsave, &gdev->line_state_lock) + raw_notifier_chain_unregister(&gdev->line_state_notifier, + &cdev->lineinfo_changed_nb); out_free_bitmap: gpio_device_put(gdev); bitmap_free(cdev->watched_lines); @@ -2779,8 +2781,9 @@ static int gpio_chrdev_release(struct inode *inode, struct file *file) blocking_notifier_chain_unregister(&gdev->device_notifier, &cdev->device_unregistered_nb); - atomic_notifier_chain_unregister(&gdev->line_state_notifier, - &cdev->lineinfo_changed_nb); + scoped_guard(write_lock_irqsave, &gdev->line_state_lock) + raw_notifier_chain_unregister(&gdev->line_state_notifier, + &cdev->lineinfo_changed_nb); bitmap_free(cdev->watched_lines); gpio_device_put(gdev); kfree(cdev); diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index e5eb3f0ee071..b8197502a5ac 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -1075,7 +1075,8 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data, } } - ATOMIC_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier); + rwlock_init(&gdev->line_state_lock); + RAW_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier); BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier); ret = init_srcu_struct(&gdev->srcu); @@ -4361,8 +4362,9 @@ EXPORT_SYMBOL_GPL(gpiod_set_array_value_cansleep); void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action) { - atomic_notifier_call_chain(&desc->gdev->line_state_notifier, - action, desc); + guard(read_lock_irqsave)(&desc->gdev->line_state_lock); + + raw_notifier_call_chain(&desc->gdev->line_state_notifier, action, desc); } /** diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h index a738e6c647d8..58f64056de77 100644 --- a/drivers/gpio/gpiolib.h +++ b/drivers/gpio/gpiolib.h @@ -16,6 +16,7 @@ #include #include #include +#include #include #include @@ -47,6 +48,7 @@ * @list: links gpio_device:s together for traversal * @line_state_notifier: used to notify subscribers about lines being * requested, released or reconfigured + * @line_state_lock: RW-spinlock protecting the line state notifier * @line_state_wq: used to emit line state events from a separate thread in * process context * @device_notifier: used to notify character device wait queues about the GPIO @@ -75,7 +77,8 @@ struct gpio_device { const char *label; void *data; struct list_head list; - struct atomic_notifier_head line_state_notifier; + struct raw_notifier_head line_state_notifier; + rwlock_t line_state_lock; struct workqueue_struct *line_state_wq; struct blocking_notifier_head device_notifier; struct srcu_struct srcu;