Re: [bug report] gpiolib: use a mutex to protect the list of GPIO devices

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Jan 15, 2024 at 11:50:52AM +0300, Dan Carpenter wrote:
> Hello Bartosz Golaszewski,
> 
> The patch 65a828bab158: "gpiolib: use a mutex to protect the list of
> GPIO devices" from Dec 15, 2023 (linux-next), leads to the following
> Smatch static checker warning:
> 
> 	drivers/net/wireless/ath/ath9k/hw.c:2836 ath9k_hw_gpio_get()
> 	warn: sleeping in atomic context
> 
> drivers/net/wireless/ath/ath9k/hw.c
>     2826                         val = MS_REG_READ(AR9285, gpio);
>     2827                 else if (AR_SREV_9280(ah))
>     2828                         val = MS_REG_READ(AR928X, gpio);
>     2829                 else if (AR_DEVID_7010(ah))
>     2830                         val = REG_READ(ah, AR7010_GPIO_IN) & BIT(gpio);
>     2831                 else if (AR_SREV_9300_20_OR_LATER(ah))
>     2832                         val = REG_READ(ah, AR_GPIO_IN(ah)) & BIT(gpio);
>     2833                 else
>     2834                         val = MS_REG_READ(AR, gpio);
>     2835         } else if (BIT(gpio) & ah->caps.gpio_requested) {
> --> 2836                 val = gpio_get_value(gpio) & BIT(gpio);
>                                ^^^^^^^^^^^^^^
> 
>     2837         } else {
>     2838                 WARN_ON(1);
>     2839         }
>     2840 
>     2841         return !!val;
>     2842 }
> 
> Before gpio_get_value() took a spinlock but now it takes a mutex
> (actually a rw semaphor now).  The call tree where we are in atomic
> context is:
> 
> ath_btcoex_period_timer() <- disables preempt
> -> ath_detect_bt_priority()
>    -> ath9k_hw_gpio_get()
> 
> Another warning this change causes is:
> 
> drivers/input/keyboard/matrix_keypad.c:95 enable_row_irqs() warn: sleeping in atomic context
> matrix_keypad_scan() <- disables preempt
> -> enable_row_irqs()
> 
> drivers/input/keyboard/matrix_keypad.c:108 disable_row_irqs() warn: sleeping in atomic context
> matrix_keypad_interrupt() <- disables preempt
> -> disable_row_irqs()

Now that that operation becomes heavier we should convert row GPIOs into
interrupt numbers in probe() and then this issue will go away.

Thanks.

-- 
Dmitry