linux-kernel - Re: Question about apds990x.ko

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Date:   Thu, 10 Aug 2017 18:11:44 +0300
From:   Anton Volkov <avolkov@...ras.ru>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: Re: Question about apds990x.ko

The author of this driver as well as bh1770glc.ko is Samu Onkalo. His 
e-mail that was found as a contact in the module's source is invalid. I 
tried to add him previous time (Question about bh1770glc.ko). The 
message was not delivered then.

On 10.08.2017 18:07, Greg KH wrote:
> 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
> 

-- 
-- Anton Volkov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: avolkov@...ras.ru