kprobes/x86: Disable preemption in optprobe

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@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>