perf/core: Use perf_cgroup_info->active to check if cgroup is active

Since we use perf_cgroup_set_timestamp() to start cgroup time and
set active to 1, then use update_cgrp_time_from_cpuctx() to stop
cgroup time and set active to 0.

We can use info->active directly to check if cgroup is active.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220329154523.86438-3-zhouchengming@bytedance.com

Author: Chengming Zhou

kernel/events/core.c

@@ -780,7 +780,6 @@ static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx,
 static inline void update_cgrp_time_from_event(struct perf_event *event)
 {
 	struct perf_cgroup_info *info;
-	struct perf_cgroup *cgrp;
 
 	/*
 	 * ensure we access cgroup data only when needed and
@@ -789,14 +788,12 @@ static inline void update_cgrp_time_from_event(struct perf_event *event)
 	if (!is_cgroup_event(event))
 		return;
 
-	cgrp = perf_cgroup_from_task(current, event->ctx);
+	info = this_cpu_ptr(event->cgrp->info);
 	/*
 	 * Do not update time when cgroup is not active
 	 */
-	if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup)) {
-		info = this_cpu_ptr(event->cgrp->info);
+	if (info->active)
 		__update_cgrp_time(info, perf_clock(), true);
-	}
 }
 
 static inline void