The idle-thread-preemption-fix.patch introduced a race, which is not
critical, but might give us an extra turn through the scheduler.  When
interrupts are reenabled in entry.c and an interrupt occures before we
reach the add_preempt_schedule() in preempt_schedule we get rescheduled
again in the return from interrupt path.

The patch prevents this by leaving interrupts disabled and calling a a
seperate function preempt_schedule_irq().

This split adds different plausibility checks for irq context calls and
kernel calls.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>