Fix scheduling latencies in the MTRR-setting codepath.  Also, fix bad bug:
MTRR's _must_ be set with interrupts disabled!

From: Bernard Blackham <bernard@blackham.com.au>

The patch sched-fix-scheduling-latencies-in-mttr in recent -mm kernels has
the bad side-effect of re-enabling interrupts even if they were disabled.
This caused bugs in Software Suspend 2 which reenabled MTRRs whilst
interrupts were already disabled.

Attached is a replacement patch which uses spin_lock_irqsave instead of
spin_lock_irq.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>