linux-kernel - Re: A potential data race in drivers/iio/adc/berlin2-adc.ko

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Date:   Thu, 18 Mar 2021 09:27:52 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Pavel Andrianov <andrianov@...ras.ru>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     ldv-project@...uxtesting.org,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: A potential data race in drivers/iio/adc/berlin2-adc.ko

On 3/18/21 9:07 AM, Pavel Andrianov wrote:
> Hi,
>
> berlin2_adc_probe [1] registers two interrupt handlers: 
> berlin2_adc_irq [2]
> and berlin2_adc_tsen_irq [3]. The interrupt handlers operate with the 
> same data, for example, modify
> priv->data with different masks:
>
> priv->data &= BERLIN2_SM_ADC_MASK;
> and
> priv->data &= BERLIN2_SM_TSEN_MASK;
>
> If the two interrupt handlers are executed simultaneously, a potential 
> data race takes place. So, the question is if the situation is 
> possible. For example, in the case of the handlers are executed on 
> different CPU cores.
>
> Best regards,
> Pavel
>
> [1] 
> https://elixir.bootlin.com/linux/latest/source/drivers/iio/adc/berlin2-adc.c#L283 
>
> [2] 
> https://elixir.bootlin.com/linux/latest/source/drivers/iio/adc/berlin2-adc.c#L239 
>
> [3] 
> https://elixir.bootlin.com/linux/latest/source/drivers/iio/adc/berlin2-adc.c#L259
>
Looking at the code there are two functions. berlin2_adc_tsen_read() and 
berlin2_adc_read(). These two function are take the same mutex and can 
not run concurrently. At the beginning of the protected section the 
corresponding interrupt for that function is enabled and at the end 
disabled. So at least if the hardware works correctly those two 
interrupts will never fire at the same time.

Now, if the hardware misbehaves the two interrupts could still fire at 
the same time.

- Lars