linux-kernel - Re: BUILD_BUG_ON() breaks sparse gfp

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Date:	Fri, 15 Apr 2011 09:45:56 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Dave Hansen <dave@...1.net>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <JBeulich@...ell.com>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: BUILD_BUG_ON() breaks sparse gfp_t checks

On Thu, 14 Apr 2011, Dave Hansen wrote:

> On Thu, 2011-04-14 at 13:22 -0700, Andrew Morton wrote:
> > The kernel calls gfp_zone() with a constant arg in very few places.
> > This?
> >
> > --- a/include/linux/gfp.h~a
> > +++ a/include/linux/gfp.h
> > @@ -249,14 +249,9 @@ static inline enum zone_type gfp_zone(gf
> >
> >         z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &
> >                                          ((1 << ZONES_SHIFT) - 1);
> > -
> > -       if (__builtin_constant_p(bit))
> > -               BUILD_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> > -       else {
> >  #ifdef CONFIG_DEBUG_VM
> > -               BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> > +       BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> >  #endif
> > -       }
> >         return z;
> >  }
>
> That definitely makes sparse happier.  I hope the folks on cc will chime
> in if they wanted something special at build time.

You can also remove the #ifdef. Use VM_BUG_ON.

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