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From: Daniel Phillips <phillips@arcor.de>
To: Sandy Harris <pashley@storm.ca>, Oliver Xymoron <oxymoron@waste.org>
Subject: Re: spinlock assertion macros
Date: Fri, 12 Jul 2002 02:56:59 +0200
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Cc: Jesse Barnes <jbarnes@sgi.com>, Andreas Dilger <adilger@clusterfs.com>,
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On Friday 12 July 2002 01:52, Sandy Harris wrote:
> 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.

MUST_NOT_HOLD is already in Jesse's patch he posted earlier today,
though I imagine it would be used rarely if at all.

!MUST_NOT_HOLD(&lock) is an error, MUST_NOT_HOLD is a statement not a
function.

-- 
Daniel
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