[tip: perf/urgent] perf: Fix dangling cgroup pointer in cpuctx

[tip-bot2 for Yeoreum Yun]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     3b7a34aebbdf2a4b7295205bf0c654294283ec82
Gitweb:        https://git.kernel.org/tip/3b7a34aebbdf2a4b7295205bf0c654294283ec82
Author:        Yeoreum Yun <yeoreum.yun@xxxxxxx>
AuthorDate:    Mon, 02 Jun 2025 19:40:49 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 05 Jun 2025 14:37:52 +02:00

perf: Fix dangling cgroup pointer in cpuctx

Commit a3c3c6667("perf/core: Fix child_total_time_enabled accounting
bug at task exit") moves the event->state update to before
list_del_event(). This makes the event->state test in list_del_event()
always false; never calling perf_cgroup_event_disable().

As a result, cpuctx->cgrp won't be cleared properly; causing havoc.

Fixes: a3c3c6667("perf/core: Fix child_total_time_enabled accounting bug at task exit")
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: David Wang <00107082@xxxxxxx>
Link: https://lore.kernel.org/all/aD2TspKH%2F7yvfYoO@xxxxxxxxxxxxxxx/
---
 kernel/events/core.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1cc98b9..d786083 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2120,18 +2120,6 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
 	if (event->group_leader == event)
 		del_event_from_groups(event, ctx);
 
-	/*
-	 * If event was in error state, then keep it
-	 * that way, otherwise bogus counts will be
-	 * returned on read(). The only way to get out
-	 * of error state is by explicit re-enabling
-	 * of the event
-	 */
-	if (event->state > PERF_EVENT_STATE_OFF) {
-		perf_cgroup_event_disable(event, ctx);
-		perf_event_set_state(event, PERF_EVENT_STATE_OFF);
-	}
-
 	ctx->generation++;
 	event->pmu_ctx->nr_events--;
 }
@@ -2488,11 +2476,14 @@ __perf_remove_from_context(struct perf_event *event,
 		state = PERF_EVENT_STATE_EXIT;
 	if (flags & DETACH_REVOKE)
 		state = PERF_EVENT_STATE_REVOKED;
-	if (flags & DETACH_DEAD) {
-		event->pending_disable = 1;
+	if (flags & DETACH_DEAD)
 		state = PERF_EVENT_STATE_DEAD;
-	}
+
 	event_sched_out(event, ctx);
+
+	if (event->state > PERF_EVENT_STATE_OFF)
+		perf_cgroup_event_disable(event, ctx);
+
 	perf_event_set_state(event, min(event->state, state));
 
 	if (flags & DETACH_GROUP)