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Question about apds990x.ko

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  Question about apds990x.ko Anton Volkov <avolkov@ispras.ru> - 2017-08-10 17:00 +0200
    Re: Question about apds990x.ko Greg KH <gregkh@linuxfoundation.org> - 2017-08-10 17:10 +0200
      Re: Question about apds990x.ko Anton Volkov <avolkov@ispras.ru> - 2017-08-10 17:20 +0200

#1708698 — Question about apds990x.ko

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?

Thank you for your time.

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

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#1708713

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

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#1708719

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@ispras.ru

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