linux-kernel - Re: [PATCH] nfsd: lockdep annotation

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Message-ID: <17645.23129.674328.872688@cse.unsw.edu.au>
Date:	Thu, 24 Aug 2006 17:50:49 +1000
From:	Neil Brown <neilb@...e.de>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] nfsd: lockdep annotation

On Thursday August 24, arjan@...radead.org wrote:
> On Thu, 2006-08-24 at 16:12 +1000, Neil Brown wrote:
> > 
> > I had flags the fh_lock in nfsd_setattr a I_MUTEX_CHILD which you
> > didn't however I see that isn't needed (Why do we have PARENT and
> > CHILD and NORMAL.... you would think that any two would do ??)
> 
> for cross directory renames 3 are needed ;(

I see....
If one of the source/dest directories is an ancestor to the other
it gets _PARENT while the descendent gets _CHILD,
otherwise the destination gets _PARENT and the source gets _CHILD.
I guess the terms 'PARENT' and 'CHILD' refer more to the relationship
of the locks than the relationship of the directories.

(If the destination name exists, it gets locked with _NORMAL)

I still find the terminology a bit confusing.
 _GRANDPARENT -> _PARENT -> _NORMAL

would make more sense to me, but maybe it isn't that important.

Thanks for the explanation.

NeilBrown
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