linux-kernel - [PATCH 5.16 247/285] perf/core: Inherit event

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Date:   Tue, 12 Apr 2022 08:31:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH 5.16 247/285] perf/core: Inherit event_caps

From: Namhyung Kim <namhyung@...nel.org>

commit e3265a4386428d3d157d9565bb520aabff8b4bf0 upstream.

It was reported that some perf event setup can make fork failed on
ARM64.  It was the case of a group of mixed hw and sw events and it
failed in perf_event_init_task() due to armpmu_event_init().

The ARM PMU code checks if all the events in a group belong to the
same PMU except for software events.  But it didn't set the event_caps
of inherited events and no longer identify them as software events.
Therefore the test failed in a child process.

A simple reproducer is:

  $ perf stat -e '{cycles,cs,instructions}' perf bench sched messaging
  # Running 'sched/messaging' benchmark:
  perf: fork(): Invalid argument

The perf stat was fine but the perf bench failed in fork().  Let's
inherit the event caps from the parent.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: <stable@...r.kernel.org>
Link: https://lkml.kernel.org/r/20220328200112.457740-1-namhyung@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/events/core.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11626,6 +11626,9 @@ perf_event_alloc(struct perf_event_attr

 	event->state		= PERF_EVENT_STATE_INACTIVE;

+	if (parent_event)
+		event->event_caps = parent_event->event_caps;
+
 	if (event->attr.sigtrap)
 		atomic_set(&event->event_limit, 1);