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Date: Thu, 11 Jul 2002 19:52:45 -0400
From: Sandy Harris <pashley@storm.ca>
Organization: Flashman's Dragoons
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To: Oliver Xymoron <oxymoron@waste.org>
CC: Daniel Phillips <phillips@arcor.de>, Jesse Barnes <jbarnes@sgi.com>,
       Andreas Dilger <adilger@clusterfs.com>,
       kernel-janitor-discuss 
	<kernel-janitor-discuss@lists.sourceforge.net>,
       linux-kernel@vger.kernel.org
Subject: Re: spinlock assertion macros
References: <Pine.LNX.4.44.0207111131550.15441-100000@waste.org>
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Oliver Xymoron wrote:
> 
> On Thu, 11 Jul 2002, Daniel Phillips wrote:
> 
> > I was thinking of something as simple as:
> >
> >    #define spin_assert_locked(LOCK) BUG_ON(!spin_is_locked(LOCK))
> >
> > but in truth I'd be happy regardless of the internal implementation.  A note
> > on names: Linus likes to shout the names of his BUG macros.  I've never been
> > one for shouting, but it's not my kernel, and anyway, I'm happy he now likes
> > asserts.  I bet he'd like it more spelled like this though:
> >
> >    MUST_HOLD(&lock);
> 
> I prefer that form too.

Is it worth adding MUST_NOT_HOLD(&lock) in an attempt to catch potential
deadlocks?

Say that if two or more of locks A, B and C are to be taken, then
they must be taken in that order. You might then have code like:

	MUST_NOT_HOLD(&lock_B) ;
	MUST_NOT_HOLD(&lock_C) ;
	spinlock(&lock_A) ;

I think you need a separate asertion for this !MUST_NOT_HOLD(&lock)
has different semantics.