linux-kernel - Re: Question about apds990x.ko

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Date:   Thu, 10 Aug 2017 08:07:55 -0700
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Anton Volkov <avolkov@...ras.ru>
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: Re: Question about apds990x.ko

On Thu, Aug 10, 2017 at 05:57:30PM +0300, Anton Volkov wrote:
> Hello.
> 
> While searching for races in the Linux kernel I've come across
> "drivers/misc/apds990x.ko" module. Here are questions that I came up with
> while analyzing results. Lines are given using the info from Linux v4.12.
> 
> Consider the following case:
> 
> Thread 1:                      Thread 2:
> apds990x_suspend
> apds990x_resume                apds990x_irq
> -> apds990x_chip_on              if (!pm_runtime_suspended
>                                                   (chip->client->dev)){
>    -> apds990x_configure           if (status & APDS990X_ST_AINT) {
>         chip->again_meas = 1         chip->again_meas = chip->again_next
>         (apds990x.c: line 571)       (apds990x.c: line 505)
>                                    }
>                                   }
> 
> First question. Is this race feasible from your point of view?
> Second question. The check for the device suspension status
> (pm_runtime_suspended()) is present in the interrupt handler, but the
> functions pm_runtime_set_suspended / pm_runtime_set_active are not used in
> apds990x_suspend / apds990x_resume respectively. Do you know about any other
> method being used to make the modification of suspension status?

No idea, sorry.  Maybe the driver authors know?

greg k-h