Re: [PATCH v7 4/9] rtc: abx80x: properly handle shared IRQs

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] rtc: abx80x: race condition loses interrupts due to flawed W0C status register clearing
--

commit 27cfcb7135851594344aa538f01f8ef1328d2392
Author: Antoni Pokusinski <apokusinski01@gmail.com>

rtc: abx80x: properly handle shared IRQs

This commit updates the abx80x RTC interrupt handler to only return
IRQ_HANDLED and clear the status register when the alarm or watchdog flags
are set. It aims to properly support IRQF_SHARED by returning IRQ_NONE
for unrelated interrupts.

> diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c
> --- a/drivers/rtc/rtc-abx80x.c
> +++ b/drivers/rtc/rtc-abx80x.c

[ ... ]

> @@ -284,9 +291,15 @@ static irqreturn_t abx80x_handle_irq(int irq, void *dev_id)
>  	if (status & ABX8XX_STATUS_WDT)
>  		dev_alert(&client->dev, "watchdog timeout interrupt.\n");
>  
> -	i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS, 0);
> +	status_flags_clear = status & (ABX8XX_STATUS_AF | ABX8XX_STATUS_WDT);
>  
> -	return IRQ_HANDLED;
> +	if (status_flags_clear) {
> +		i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS,
> +					  status & ~status_flags_clear);

[Severity: High]
Does this logic introduce a race condition that loses late-arriving interrupts
in abx80x_handle_irq()?

Because the ABX8XX_REG_STATUS register is W0C (write-0-to-clear), any bit
written as 0 will be cleared in hardware. 

The expression status & ~status_flags_clear forces a 0 for all bits that
were 0 during the initial read. If a new hardware interrupt asserts between
the read and this write, its status bit will be newly set to 1 in hardware.
However, writing back the old status value forces a 0 for that new bit,
silently clearing it and losing the event.

To preserve unhandled or newly asserted bits, the correct write value for a
W0C register is ~status_flags_clear instead.

> +		return IRQ_HANDLED;
> +	}
> +
> +	return IRQ_NONE;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260916205138.16771-1-apokusinski01@gmail.com?part=4