PERF_ATTACH_CONTEXT
WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
event->attach_state |= PERF_ATTACH_CONTEXT;
if (!(event->attach_state & PERF_ATTACH_CONTEXT))
event->attach_state &= ~PERF_ATTACH_CONTEXT;
if (sibling->attach_state & PERF_ATTACH_CONTEXT) {
(PERF_ATTACH_CONTEXT|PERF_ATTACH_GROUP));