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Subject: Re: [PATCH 0/3] Synaptics - fix lockdep warnings
From: Arjan van de Ven <arjan@infradead.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Jiri Kosina <jikos@jikos.cz>, lkml <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>
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Date: Fri, 15 Sep 2006 07:33:24 +0200
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On Thu, 2006-09-14 at 15:11 -0400, Dmitry Torokhov wrote:
> On 9/14/06, Arjan van de Ven <arjan@infradead.org> wrote:
> >
> > >
> > > I think it is - as far as I understand the reason for not tracking
> > > every lock individually is just that it is too expensive to do by
> > > default.
> >
> > that is not correct. While it certainly plays a role,
> > the other reason is that you can find out "class" level locking rules
> > (such as inode->i_mutex comes before <other lock>) for all inodes at a
> > time; eg no need to see every inode do this before you can find the
> > deadlock.
> >
> 
> OK, I can see that. However you must agree that for certain locks we
> do want to track them individually, right?

I agree that if locks really represent different objects with different
locking semantics they should not share the class. Lockdep provides a
mechanism for that; however I'm very afraid that for the input layer,
they really are not that, they are not different objects with different
semantics; they are the same objects with nesting semantics! In that
case the "separate lock class" stuff has only disadvantages.
The worst thing is that as I understand it this separate class is
*dynamic*. Eg it's not even "one class per driver" ;(


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