[IA64] Fix the order of atomic operations in restore_previous_kprobes on ia64

Fix the order of atomic operations to prevent overwriting prev_kprobe[0].
To pop values from stack, we must decrement stack index right AFTER
reading values.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/kprobes.c

@@ -381,9 +381,10 @@ static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	unsigned int i;
-	i = atomic_sub_return(1, &kcb->prev_kprobe_index);
-	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i].kp;
-	kcb->kprobe_status = kcb->prev_kprobe[i].status;
+	i = atomic_read(&kcb->prev_kprobe_index);
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i-1].kp;
+	kcb->kprobe_status = kcb->prev_kprobe[i-1].status;
+	atomic_sub(1, &kcb->prev_kprobe_index);
 }
 
 static void __kprobes set_current_kprobe(struct kprobe *p,