1 files changed, 36 insertions, 5 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index a654b8a..ee20d4c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2217,6 +2217,33 @@ static int group_can_go_on(struct perf_event *event,
 	return can_add_hw;
 }
 
+/*
+ * Complement to update_event_times(). This computes the tstamp_* values to
+ * continue 'enabled' state from @now, and effectively discards the time
+ * between the prior tstamp_stopped and now (as we were in the OFF state, or
+ * just switched (context) time base).
+ *
+ * This further assumes '@event->state == INACTIVE' (we just came from OFF) and
+ * cannot have been scheduled in yet. And going into INACTIVE state means
+ * '@event->tstamp_stopped = @now'.
+ *
+ * Thus given the rules of update_event_times():
+ *
+ *   total_time_enabled = tstamp_stopped - tstamp_enabled
+ *   total_time_running = tstamp_stopped - tstamp_running
+ *
+ * We can insert 'tstamp_stopped == now' and reverse them to compute new
+ * tstamp_* values.
+ */
+static void __perf_event_enable_time(struct perf_event *event, u64 now)
+{
+	WARN_ON_ONCE(event->state != PERF_EVENT_STATE_INACTIVE);
+
+	event->tstamp_stopped = now;
+	event->tstamp_enabled = now - event->total_time_enabled;
+	event->tstamp_running = now - event->total_time_running;
+}
+
 static void add_event_to_ctx(struct perf_event *event,
 			       struct perf_event_context *ctx)
 {
@@ -2224,9 +2251,12 @@ static void add_event_to_ctx(struct perf_event *event,
 
 	list_add_event(event, ctx);
 	perf_group_attach(event);
-	event->tstamp_enabled = tstamp;
-	event->tstamp_running = tstamp;
-	event->tstamp_stopped = tstamp;
+	/*
+	 * We can be called with event->state == STATE_OFF when we create with
+	 * .disabled = 1. In that case the IOC_ENABLE will call this function.
+	 */
+	if (event->state == PERF_EVENT_STATE_INACTIVE)
+		__perf_event_enable_time(event, tstamp);
 }
 
 static void ctx_sched_out(struct perf_event_context *ctx,
@@ -2471,10 +2501,11 @@ static void __perf_event_mark_enabled(struct perf_event *event)
 	u64 tstamp = perf_event_time(event);
 
 	event->state = PERF_EVENT_STATE_INACTIVE;
-	event->tstamp_enabled = tstamp - event->total_time_enabled;
+	__perf_event_enable_time(event, tstamp);
 	list_for_each_entry(sub, &event->sibling_list, group_entry) {
+		/* XXX should not be > INACTIVE if event isn't */
 		if (sub->state >= PERF_EVENT_STATE_INACTIVE)
-			sub->tstamp_enabled = tstamp - sub->total_time_enabled;
+			__perf_event_enable_time(sub, tstamp);
 	}
 }