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

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Date:	Thu, 2 Aug 2007 02:58:22 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Mikael Pettersson <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, Aug 02, 2007 at 02:06:27AM +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,

Probably.  Or handle -ENOSYS in the callers -- but that's more
work, and would cease to be necessary once everyone implements
futex_atomic_cmpxchg_inatomic().


> but that's a different issue from the UP case which I really do
> want to see fixed.

ACK.
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