linux-kernel - Possible race in ucb1400

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Date:   Tue, 15 Aug 2017 16:46:25 +0300
From:   Anton Volkov <avolkov@...ras.ru>
To:     marek.vasut@...il.com, dmitry.torokhov@...il.com
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: Possible race in ucb1400_ts.ko

Hello.

While searching for races in the Linux kernel I've come across 
"drivers/input/touchscreen/ucb1400_ts.ko" module. Here is a question 
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:
ucb1400_suspend
->ucb1400_ts_start
     ucb->stopped = false
     enable_irq()

ucb1400_resume
->ucb1400_ts_stop           ucb1400_irq
     ucb->stopped = true       while(!ucb->stopped && ...)
     (ucb1400_ts.c: line 230)  (ucb1400_ts.c: line 202)
     disable_irq()

The value of ucb->stopped may be changed in the midst of 'while' loop 
iterations or prevent all of them from happening. Is this feasible from 
your point of view? If so, is it a benign race or is it serious?

Thank you for your time.

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