[PATCH] utilization of kprobe_mutex is incorrect on x86_64

The up()/down() orders are incorrect in arch/x86_64/kprobes.c file.
kprobe_mutext is used to protect the free kprobe instruction slot list.
arch_prepare_kprobe applies for a slot from the free list, and
arch_remove_kprobe returns a slot to the free list.  The incorrect up()/down()
orders to operate on kprobe_mutex fail to protect the free list.  If 2 threads
try to get/return kprobe instruction slot at the same time, the free slot list
might be broken, or a free slot might be applied by 2 threads.

Signed-off-by: Zhang Yanmin <Yanmin.zhang@intel.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>