From: Pavel Andrianov <andrianov@ispras.ru>
To: Jonathan Cameron <jic23@kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>,
Lars-Peter Clausen <lars@metafoo.de>,
Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
Alexander Koch <mail@alexanderkoch.net>,
Vaishali Thakkar <vaishali.thakkar@oracle.com>,
ldv-project@linuxtesting.org,
Andreas Dannenberg <dannenberg@ti.com>
Subject: Re: A potential bug in drivers/iio/light/opt3001.ko
Date: Mon, 5 Sep 2016 17:15:30 +0300 [thread overview]
Message-ID: <0bb361fc-5912-eae2-e081-05e45f774798@ispras.ru> (raw)
In-Reply-To: <61728463-8bd8-c68e-ef4a-7a3e0ddd7899@kernel.org>
03.09.2016 19:38, Jonathan Cameron пишет:
> On 31/08/16 11:23, Pavel Andrianov wrote:
>> 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.
> Good find. Will need reordering to set the ok_to_ignore_lock first.
> Whether it ever actually happens will depend on just how long that EOC
> interrupt takes to happen. Still it's a theoretical problem with
> a fairly simple fix so let's fix it.
>>
>> 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.
>>
> Agreed - looks like some reordering is needed here as well.
>
> Jonathan
>
In opt3001_get_lux has a comment, that i2c_smbus_write_word_swapped
(line 246) enables interrupt mechanism. If an interrupt can not arise
before the function, the assignments to both of flags should be moved
before i2c_smbus_write_word_swapped and this is the best fix for both of
issues.
Do you know if my assumption is correct and interrupts are disabled
before i2c_smbus_write_word_swapped call?
--
Pavel Andrianov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: andrianov@ispras.ru
next prev parent reply other threads:[~2016-09-05 14:15 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-31 10:23 A potential bug in drivers/iio/light/opt3001.ko Pavel Andrianov
2016-09-03 16:38 ` Jonathan Cameron
2016-09-05 14:15 ` Pavel Andrianov [this message]
2016-09-05 20:04 ` Jonathan Cameron
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