When the generic IRQ stuff went in, it seems that HARDIRQ_BITS got bumped
from 9 (for ppc64) up to 12.  Consequently, the PREEMPT_ACTIVE bit is now
within HARDIRQ_MASK, and I get in_interrupt() falsely returning true when
PREEMPT_ACTIVE is set, and thus a BUG_ON tripping in arch/ppc64/mm/tlb.c.

The patch below fixes this by changing PREEMPT_ACTIVE to 0x10000000.  I
have changed the PREEMPT_ACTIVE definitions for each of the architectures
that define CONFIG_GENERIC_HARDIRQS (i386, ppc, ppc64, x86_64) and fixed
the comment in include/linux/hardirq.h.  We could perhaps move the
PREEMPT_ACTIVE definition to include/linux/hardirq.h - I don't know why it
is still per-arch.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>