linux-kernel - Question about apds990x.ko

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Message-ID: <6bd7a5d0-97ef-4e04-6914-9e287c7be767@ispras.ru>
Date:   Thu, 10 Aug 2017 17:57:30 +0300
From:   Anton Volkov <avolkov@...ras.ru>
To:     arnd@...db.de, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: 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@...ras.ru