On Tue, 6 Mar 2012, Andrew Morton wrote:
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -1611,6 +1611,7 @@ unsigned slab_node(struct mempolicy *policy)
> >
> > default:
> > BUG();
> > + return numa_node_id();
> > }
> > }
>
> Wait. If the above code generated a warning then surely we get a *lot*
> of warnings! I'd expect that a lot of code assumes that BUG() never
> returns?
>
allyesconfig with CONFIG_BUG=n results in 50 such warnings tree wide, and
this is the only one in mm/*.
> Also, does CONIG_BUG=n even make sense? If we got here and we know
> that the kernel has malfunctioned, what point is there in pretending
> otherwise? Odd.
>
I don't suspect we'll be very popular if we try to remove it, I can see
how it would be useful when BUG() is used when the problem isn't really
fatal (to stop something like disk corruption), like the above case isn't.
If policy->mode isn't one of MPOL_{BIND,INTERLEAVE,PREFERRED} then we'd
want WARN_ON_ONCE() at best; someone either didn't test their patch or
we've flipped a bit, but the kernel can run happily along using the local
node for slab allocations while still notifying the user.
mm/mempolicy.c misuses BUG() in every case, Not having the perfect NUMA
optimizations is surely annoying, but let's not crash someone's kernel.
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