[PATCH] perf: Fix scheduling regression of pinned groups

[Alexander Shishkin]

Commit 487f05e18a ("perf/core: Optimize event rescheduling on active
contexts") erronously assumed that event's 'pinned' setting determines
whether the event belongs to a pinned group or not, but in fact, it's
the group leader's pinned state that matters. This was discovered by
Vince in a test case where two instruction counters are grouped, the
group leader is pinned, but the other event is not; in the regressed
case the counters were off by 33% (the difference between events'
periods), but should be the same within the error margin.

This fixes the problem by looking at the group leader's pinning.

Reported-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Fixes: 487f05e18a ("perf/core: Optimize event rescheduling on active contexts")
Cc: stable@xxxxxxxxxxxxxxx
---
 kernel/events/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index bc63f8db1b..1edbaf94dd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1451,6 +1451,13 @@ static enum event_type_t get_event_type(struct perf_event *event)
 
 	lockdep_assert_held(&ctx->lock);
 
+	/*
+	 * It's 'group type', really, because if our group leader is
+	 * pinned, so are we.
+	 */
+	if (event->group_leader != event)
+		event = event->group_leader;
+
 	event_type = event->attr.pinned ? EVENT_PINNED : EVENT_FLEXIBLE;
 	if (!ctx->task)
 		event_type |= EVENT_CPU;
-- 
2.11.0