linux-kernel - Re: [PATCH][RFC] unbreak generic futex_atomic_cmpxchg

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Message-Id: <200708020006.l7206RoY009376@harpo.it.uu.se>
Date:	Thu, 2 Aug 2007 02:06:27 +0200 (MEST)
From:	Mikael Pettersson <mikpe@...uu.se>
To:	buytenh@...tstofly.org, mikpe@...uu.se
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	rmk@....linux.org.uk, tglx@...utronix.de
Subject: Re: [PATCH][RFC] unbreak generic futex_atomic_cmpxchg_inatomic() on UP

On Thu, 2 Aug 2007 01:49:02 +0200, Lennert Buytenhek wrote:
> On Thu, Aug 02, 2007 at 01:00:21AM +0200, Mikael Pettersson wrote:
> 
> > @@ -52,7 +53,34 @@ futex_atomic_op_inuser (int encoded_op, 
> >  static inline int
> >  futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
> >  {
> > +#ifdef CONFIG_SMP
> >  	return -ENOSYS;
> > +#else
> 
> Since the callers of futex_atomic_cmpxchg_inatomic() don't really
> seem prepared to deal with -ENOSYS (e.g. the handle_futex_death()
> infinite loop when it gets -ENOSYS), it seems better never to
> return -ENOSYS from this function at all.
> 
> What if you just stick an #error in here in the SMP case?

The problem with #error is that it would cause compile-time
regressions. I assume that e.g. alpha supports building SMP
kernels, but #error would prevent that.

Thus I opted to fix the UP case while leaving the SMP case
unchanged. Actually I think the SMP case should be a BUG()
rather than -ENOSYS, but that's a different issue from the
UP case which I really do want to see fixed.

/Mikael
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