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Subject: Re: [PATCH 1/8] lockdep: fix recursive read lock validation
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Bart Van Assche <bart.vanassche@gmail.com>
Cc: ego@in.ibm.com, linux-kernel@vger.kernel.org,
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Date: Tue, 29 Apr 2008 19:04:03 +0200
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On Tue, 2008-04-29 at 18:29 +0200, Bart Van Assche wrote:
> On Tue, Apr 29, 2008 at 6:15 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> >
> >  > Or: whether or not to allow a sequence like "rlock(a); rlock(b);
> >  > runlock(b); runlock(a); rlock(b); rlock(a);" is something we can
> >  > choose. We do not have to forbid this sequence -- we can choose
> >  > whether or not we allow this sequence.
> >
> >  I'm utterly confused now; I never argued that it would get deadlocks;
> >  and I said I choose to not allow it from a lockdep pov. What else do you
> >  want?
> 
> So we both agree that the statement in the original e-mail (by Gautham
> R Shenoy) is wrong ? The original e-mail stated that obtaining reader
> locks in an inconsistent order is wrong.

I think the critical part is:

> It really is invalid when considered against write locks.

Aside from that it just states that inversion of lock order will be
treated as invalid - even for read locks.