sched/core: More notrace annotations

preempt_schedule_common() is marked notrace, but it does not use
_notrace() preempt_count functions and __schedule() is also not marked
notrace, which means that its perfectly possible to end up in the
tracer from preempt_schedule_common().

Steve says:

  | Yep, there's some history to this. This was originally the issue that
  | caused function tracing to go into infinite recursion. But now we have
  | preempt_schedule_notrace(), which is used by the function tracer, and
  | that function must not be traced till preemption is disabled.
  |
  | Now if function tracing is running and we take an interrupt when
  | NEED_RESCHED is set, it calls
  |
  |   preempt_schedule_common() (not traced)
  |
  | But then that calls preempt_disable() (traced)
  |
  | function tracer calls preempt_disable_notrace() followed by
  | preempt_enable_notrace() which will see NEED_RESCHED set, and it will
  | call preempt_schedule_notrace(), which stops the recursion, but
  | still calls __schedule() here, and that means when we return, we call
  | the __schedule() from preempt_schedule_common().
  |
  | That said, I prefer this patch. Preemption is disabled before calling
  | __schedule(), and we get rid of a one round recursion with the
  | scheduler.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Acked-by: Steven Rostedt <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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