[PATCH] tracing, sched: mark preempt_schedule() notrace

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Current preempt_schedule() is not marked notrace. It may be
infinite recursion in __trace_graph_return().

preempt_schedule()
  __trace_graph_return()
    ftrace_preempt_disable() (!!return false!!)
    ftrace_preempt_enable()
      preempt_enable_notrace()
         preempt_schedule() (need_resched() may be true again)


It hardly happens, but marking preempt_schedule() notrace
makes it safer.

One interesting thing is that preempt_schedule() is in
the blacklist of kprobe subsystem. "__kprobes" implies "notrace".
But preempt_schedule() cannot be marked __kprobes for it
has been marked __sched. It is in the blacklist makes me
consider this: should it be marked "notrace" -- YES.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/sched.c b/kernel/sched.c
index 5184580..2e9e209 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5534,7 +5534,7 @@ out:
  * off of preempt_enable. Kernel preemptions off return from interrupt
  * occur there and call schedule directly.
  */
-asmlinkage void __sched preempt_schedule(void)
+asmlinkage void __sched notrace preempt_schedule(void)
 {
 	struct thread_info *ti = current_thread_info();