Hi David,
this problem is wellknown and I actually thought that it was
solved. But it looks like the complex prepare_arch_switch()
etc. macros didn't make it into the 2.5 kernels for IA64. They are
needed on IA64 because we have to release the runqueue lock during
context switch. This is similar to sparc64. Thanks to John Hawks for
noticing this.
Please include this into your kernel tree.
Regards,
Erich