From: Andi Kleen <ak@muc.de>

The new domain scheduler got miscompiled on x86-64 with gcc 3.3.3-hammer,
which is shipping with some distributions.  The kernel deadlocks eventually
under light stress on SMP systems with the right options.

After some experiments it seems this simple change avoids the
miscompilation.  It also doesn't pessimize the code unduly for other
architectures.