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@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/

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1cc98b9b3c0b4e0a1c561618c53039ca30eb430d..d78608323916fa5d249948f07169cfb4f9371a50 100644 (file)
--- 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)