perf: Make clock software events consistent with general exclusion rules

The cpu/task clock events implement their own version of exclusion
on top of exclude_user and exclude_kernel.

The result is that when the event triggered in the kernel but we
have exclude_kernel set, we try to rewind using task_pt_regs.
There are two side effects of this:

- we call task_pt_regs even on kernel threads, which doesn't give
  us the desired result.
- if the event occured in the kernel, we shouldn't rewind to the
  user context. We want to actually ignore the event.

get_irq_regs() will always give us the right interrupted context, so
use its result and submit it to perf_exclude_context() that knows
when an event must be ignored.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -4164,15 +4164,8 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 	perf_sample_data_init(&data, 0);
 	data.period = event->hw.last_period;
 	regs = get_irq_regs();
-	/*
-	 * In case we exclude kernel IPs or are somehow not in interrupt
-	 * context, provide the next best thing, the user IP.
-	 */
-	if ((event->attr.exclude_kernel || !regs) &&
-			!event->attr.exclude_user)
-		regs = task_pt_regs(current);
 
-	if (regs) {
+	if (regs && !perf_exclude_event(event, regs)) {
 		if (!(event->attr.exclude_idle && current->pid == 0))
 			if (perf_event_overflow(event, 0, &data, regs))
 				ret = HRTIMER_NORESTART;