perf: Fix dangling cgroup pointer in cpuctx

JIRA: https://issues.redhat.com/browse/RHEL-78197

upstream
========
commit 3b7a34a
Author: Yeoreum Yun <yeoreum.yun@arm.com>
Date:   Mon Jun 2 19:40:49 2025 +0100

description
===========
Commit a3c3c66("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: a3c3c66("perf/core: Fix child_total_time_enabled accounting bug at task exit")
    Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Tested-by: David Wang <00107082@163.com>
    Link: https://lore.kernel.org/all/aD2TspKH%2F7yvfYoO@e129823.arm.com/

Conflicts:
==========
Different context due to not (yet) backported da916e9 ("perf:
Make perf_pmu_unregister() useable")

Signed-off-by: Michael Petlan <mpetlan@redhat.com>

Author: rfmvh

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--;
 }
@@ -2481,11 +2469,14 @@ __perf_remove_from_context(struct perf_event *event,
 	 */
 	if (flags & DETACH_EXIT)
 		state = PERF_EVENT_STATE_EXIT;
-	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)
 		perf_group_detach(event);