linux-kernel - A potential bug in drivers/iio/light/opt3001.ko

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Date:   Wed, 31 Aug 2016 13:23:39 +0300
From:   Pavel Andrianov <andrianov@...ras.ru>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Koch <mail@...xanderkoch.net>,
        Vaishali Thakkar <vaishali.thakkar@...cle.com>,
        ldv-project@...uxtesting.org
Subject: A potential bug in drivers/iio/light/opt3001.ko

Hi!

There is a bug in drivers/iio/light/opt3001.ko. Regard such case:

Thread 1                             Thread 2
-> opt3001_read_raw
   -> mutex_lock(&opt->lock)
   -> opt3001_get_lux()
     ..
     ->i2c_smbus_write_word_swapped()
             Now an interrupt comes
                                      -> opt3001_irq
                                        -> mutex_lock(&opt->lock)

This is a deadlock, as the flag ok_to_ignore_lock has not been set yet.

Regard another case:

Thread 1                             Thread 2
-> opt3001_read_raw
   -> mutex_lock(&opt->lock)
   -> opt3001_get_lux()
     ..
     -> i2c_smbus_write_word_swapped()
     opt->ok_to_ignore_lock = true;
             Now an interrupt comes
                                      -> opt3001_irq
                                        ..
                                        opt->result_ready = true
                                        wake_up()
      opt->result_ready = false;
      wait_event_timeout()

In this case the first thread misses the result and waits until timeout 
expires.

-- 
Pavel Andrianov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: andrianov@...ras.ru