Re: [PATCH] gpiolib: clear the event clock flags when a line is released

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] gpio: data race in gpiod_free_commit() causes debounce corruption
--

commit 9516d6cf1c2a072b1bec8e797ac66548d0323b06
Author: Adrian Ambrozewicz <aambrozewicz@nvidia.com>

gpiolib: clear the event clock flags when a line is released

This commit ensures that the GPIOD_FLAG_EVENT_CLOCK_REALTIME and
GPIOD_FLAG_EVENT_CLOCK_HTE flags are cleared when a GPIO line is released.
It modifies gpiod_free_commit() to clear these flags alongside others so
that they do not leak into the line info for a freed line.

> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 772c6f04f489b..c6cee872e4ae5 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2679,6 +2679,8 @@ void gpiod_free_commit(struct gpio_desc *desc)
>  		clear_bit(GPIOD_FLAG_BIAS_DISABLE, &flags);
>  		clear_bit(GPIOD_FLAG_EDGE_RISING, &flags);
>  		clear_bit(GPIOD_FLAG_EDGE_FALLING, &flags);
> +		clear_bit(GPIOD_FLAG_EVENT_CLOCK_REALTIME, &flags);
> +		clear_bit(GPIOD_FLAG_EVENT_CLOCK_HTE, &flags);
>  		clear_bit(GPIOD_FLAG_IS_HOGGED, &flags);
>  #ifdef CONFIG_OF_DYNAMIC
>  		WRITE_ONCE(desc->hog, NULL);

[Severity: High]
Does this code cause debounce corruption by clearing ownership too early?

In gpiod_free_commit(), the ownership synchronization token
(GPIOD_FLAG_REQUESTED) is cleared in desc->flags via a WRITE_ONCE() before
the function finishes cleaning up ancillary state (debounce_period_us) and
emitting the GPIO_V2_LINE_CHANGED_RELEASED notification:

drivers/gpio/gpiolib.c:gpiod_free_commit() {
    ...
		WRITE_ONCE(desc->flags, flags);
#ifdef CONFIG_GPIO_CDEV
		WRITE_ONCE(desc->debounce_period_us, 0);
#endif
		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_RELEASED);
    ...
}

This allows a concurrent request (e.g., from GPIO_V2_GET_LINE_IOCTL via
linereq_create()) to successfully acquire the GPIO line:

drivers/gpio/gpiolib.c:gpiod_request_commit() {
    ...
	if (test_and_set_bit(GPIOD_FLAG_REQUESTED, &desc->flags))
		return -EBUSY;
    ...
}

It can then configure a new debounce_period_us:

drivers/gpio/gpiolib-cdev.c:edge_detector_setup() {
    ...
		WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);
    ...
}

The original freeing thread then resumes and overwrites the newly requested
line's debounce_period_us with 0. This completely breaks software debouncing,
causing a 0-delay software debounce that will trigger its delayed work
immediately on every hardware edge. This could lead to an interrupt storm
and CPU soft lockup.

Additionally, this sends an out-of-order RELEASED notification to userspace
for a line that is currently fully requested and active.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012-gpiolib-event-clock-v1-1-aambrozewicz@nvidia.com?part=1