perf/arm-smmuv3: Fix lockdep assert in ->event_init()

Same as
https://lore.kernel.org/all/[email protected]/,
we should skip `for_each_sibling_event()` for group leader since it
doesn't have the ctx yet.

Fixes: f3c0eba ("perf: Add a few assertions")
Reported-by: Greg Thelen <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Tuan Phan <[email protected]>
Signed-off-by: Chun-Tse Shao <[email protected]>
Acked-by: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: Chun-Tse Shao

drivers/perf/arm_smmuv3_pmu.c

@@ -431,6 +431,17 @@ static int smmu_pmu_event_init(struct perf_event *event)
 			return -EINVAL;
 	}
 
+	/*
+	 * Ensure all events are on the same cpu so all events are in the
+	 * same cpu context, to avoid races on pmu_enable etc.
+	 */
+	event->cpu = smmu_pmu->on_cpu;
+
+	hwc->idx = -1;
+
+	if (event->group_leader == event)
+		return 0;
+
 	for_each_sibling_event(sibling, event->group_leader) {
 		if (is_software_event(sibling))
 			continue;
@@ -442,14 +453,6 @@ static int smmu_pmu_event_init(struct perf_event *event)
 			return -EINVAL;
 	}
 
-	hwc->idx = -1;
-
-	/*
-	 * Ensure all events are on the same cpu so all events are in the
-	 * same cpu context, to avoid races on pmu_enable etc.
-	 */
-	event->cpu = smmu_pmu->on_cpu;
-
 	return 0;
 }