linux-kernel - Re: [PATCH 01/18] lirc core device driver infrastructure

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Date:	Tue, 09 Sep 2008 15:27:18 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Sebastian Siewior <lkml@...breakpoint.cc>
CC:	Jarod Wilson <jwilson@...hat.com>, linux-kernel@...r.kernel.org,
	Jarod Wilson <jarod@...hat.com>, Janne Grunau <j@...nau.net>,
	Christoph Bartelmus <lirc@...telmus.de>,
	Mario Limonciello <superm1@...ntu.com>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 01/18] lirc core device driver infrastructure

Sebastian Siewior wrote:
>> --- /dev/null
>> +++ b/drivers/input/lirc/lirc_dev.c
...
>> +#include <linux/ioctl.h>
>> +#include <linux/fs.h>
>> +#include <linux/poll.h>
>> +#include <linux/smp_lock.h>
> if you need this than you use the BKL back. As far as I remember
> the ioctl() handler in kernel core no longer takes the BKL and I don't
> see any locking in irctl_ioctl(). 

Really?  .open() has been changed to be called without the BKL held, but 
.ioctl() is still called with BKL protection.  Currently, many .ioctl() 
implementations are replaced by .unlocked_ioctl() which take the BKL 
themselves if necessary or if it is not yet clear whether they would 
work without BKL protection.

...
>> +static struct file_operations fops = {
>> +	.read		= irctl_read,
>> +	.write		= irctl_write,
>> +	.poll		= irctl_poll,
>> +	.ioctl		= irctl_ioctl,
>> +	.open		= irctl_open,
>> +	.release	= irctl_close
>> +};

This should be audited for the following aspects:

   - Could there be a race condition between irctl_open() and
     lirc_dev_init()?  If yes, try to rework them to eliminate the race,
     or as a last resort take the BKL in irctl_open().

   - Does irctl_ioctl() require BKL protection, i.e. does it have to be
     serialized against itself and against irctl_open()?  If not, replace
     it by .unlocked_ioctl.  If yes, preferably convert it to
     .unlocked_ioctl too and add a local mutex for the necessary
     serialization.

(Added Cc: Jonathan Corbet to correct me if I'm wrong.)
-- 
Stefan Richter
-=====-==--- =--= -=--=
http://arcgraph.de/sr/
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