Re: BUILD_BUG_ON() breaks sparse gfp_t checks

From: Christoph Lameter
Date: Fri Apr 15 2011 - 10:46:08 EST


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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