kprobes/x86: Disable preemption in optprobe

Disable preemption in optprobe handler as described
in Documentation/kprobes.txt, which says:

  "Probe handlers are run with preemption disabled."
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/150581525942.32348.6359217983269060829.stgit@devboxSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/kprobes/opt.c

@@ -161,6 +161,7 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 		return;
 
 	local_irq_save(flags);
+	preempt_disable();
 	if (kprobe_running()) {
 		kprobes_inc_nmissed_count(&op->kp);
 	} else {
@@ -180,6 +181,7 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 		opt_pre_handler(&op->kp, regs);
 		__this_cpu_write(current_kprobe, NULL);
 	}
+	preempt_enable_no_resched();
 	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(optimized_callback);