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

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On 3/18/21 9:27 AM, Lars-Peter Clausen wrote:
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

Actually thinking a bit more about this the interrupt could still fire after it has been disabled since there is no synchronization between the disable and the interrupt handler. And the handler might be queued on one CPU, while the disable is running on another CPU.




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