linux-kernel - [PATCH Fix perf cgroup problem 1/2] perf/core: Fix nr_cgroups/cpuctx->cgrp is not updated correctly

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Message-Id: <20250514064758.4156497-2-luogengkun@huaweicloud.com>
Date: Wed, 14 May 2025 06:47:57 +0000
From: Luo Gengkun <luogengkun@...weicloud.com>
To: peterz@...radead.org
Cc: mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com,
	yeoreum.yun@....com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH Fix perf cgroup problem 1/2] perf/core: Fix nr_cgroups/cpuctx->cgrp is not updated correctly

Since __perf_remove_from_context updates event->state before list_del_event,
this prevents list_del_event from calling perf_cgroup_event_disable,
resulting in will not update nr_cgroups and cpuctx->cgrp.

To resolve this issue:
 1. First update the event time to ensure perf_child_detach uses
    accurate event time.
 2. Then update event->state after list_del_event completes.

Fixes: a3c3c66670ce ("perf/core: Fix child_total_time_enabled accounting bug at task exit")
Signed-off-by: Luo Gengkun <luogengkun@...weicloud.com>
---
 kernel/events/core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 95e703891b24..ecb4d852a006 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2482,12 +2482,17 @@ __perf_remove_from_context(struct perf_event *event,
 		state = PERF_EVENT_STATE_DEAD;
 	}
 	event_sched_out(event, ctx);
-	perf_event_set_state(event, min(event->state, state));
+	perf_event_update_time(event);
 	if (flags & DETACH_GROUP)
 		perf_group_detach(event);
 	if (flags & DETACH_CHILD)
 		perf_child_detach(event);
 	list_del_event(event, ctx);
+	/*
+	 * Update the event->state after list_del_event.
+	 */
+	if (flags & (DETACH_DEAD | DETACH_EXIT))
+		event->state = state;
 
 	if (!pmu_ctx->nr_events) {
 		pmu_ctx->rotate_necessary = 0;
-- 
2.34.1