Re: spinlock assertion macros

[Sandy Harris]

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.