[PATCH] x86_64: Don't schedule on exception stack on preemptive kernels

Extends an earlier patch from John Blackwood to more exception handlers
that also run on the exception stacks.

Expand the use of preempt_conditional_{sti,cli} to all cases where
interrupts are to be re-enabled during exception handling while running
on an IST stack.

Based on original patch from Jan Beulich.

Cc: John Blackwood <john.blackwood@ccur.com>
Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>