linux-kernel - Re: [PATCH 0/3] Synaptics

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Message-ID: <Pine.LNX.4.64.0609141028540.22181@twin.jikos.cz>
Date:	Thu, 14 Sep 2006 10:43:00 +0200 (CEST)
From:	Jiri Kosina <jikos@...os.cz>
To:	Dmitry Torokhov <dtor@...ightbb.com>
cc:	Andrew Morton <akpm@...l.org>, lkml <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH 0/3] Synaptics - fix lockdep warnings

On Wed, 13 Sep 2006, Dmitry Torokhov wrote:

> Unfortunately these patches do not solve the problem in general but 
> rather fix one specific codepath. As far as I can see the warnings will 
> return as soon as we add another pass-through port to the link (and I am 
> considering adding a pass-through port to the trackpoint driver so you 
> will get chain like i8042-synaptics-ptport-trackpoint-ptport-psmouse). 
> Plus they are ugly and complicate serio and psmouse cores. I really 
> don't like this *_nested business as it makes the code aware of possible 
> usage patterns instead of just being re-entrant.

Hi Dmitry,

I agree that these patches are ugly, but I wasn't able to think of any 
other way how to get rid of those lockdep warnings.

Of course the lock validator could be extended to provide API such as 
mutex_init_nolockdep(), as you already proposed before, but this also has 
it's drawbacks (for example if any other future user of ps2_init() uses 
the mutex in a really bad way, this would not be detected by lock 
validator).

Another possibility that comes to mind is extending the ps2dev structure 
with a field which would work as an subclass identifier for the device, 
and this field will be then be used as an subclass argument to 
mutex_lock_nested(). However, this requires proper setting of this field 
on the very same places on which my _nested functions are called, so it 
has the same level of generality.

Do you have any other idea? I think this should get fixed, otherwise we 
will keep receiving these reports from users again and again.

Thanks,

-- 
JiKos.
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