[PATCH 5.10.y 2/3] perf: Fix dangling cgroup pointer in cpuctx

From: Yeoreum Yun <[email protected]>

[ Upstream commit 3b7a34aebbdf2a4b7295205bf0c654294283ec82 ]

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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: David Wang <[email protected]>
Link: https://lore.kernel.org/all/aD2TspKH%[email protected]/
Stable-dep-of: 42c5ca1f0a28 ("perf/core: Fix group leader use-after-free after sibling detach")
Signed-off-by: Sasha Levin <[email protected]>
---
 kernel/events/core.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 756152374a3b9..5e4d1b090db70 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2117,18 +2117,6 @@ 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++;
 }
 
@@ -2422,6 +2410,7 @@ __perf_remove_from_context(struct perf_event *event,
 			   struct perf_event_context *ctx,
 			   void *info)
 {
+	enum perf_event_state state = PERF_EVENT_STATE_OFF;
 	unsigned long flags = (unsigned long)info;
 
 	if (ctx->is_active & EVENT_TIME) {
@@ -2430,6 +2419,12 @@ __perf_remove_from_context(struct perf_event *event,
 	}
 
 	event_sched_out(event, cpuctx, 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);
 	list_del_event(event, ctx);
-- 
2.53.0