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

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Message-Id: <20220211194154.667364-1-namhyung@kernel.org>
Date:   Fri, 11 Feb 2022 11:41:54 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>, Will Deacon <will@...nel.org>,
        stable@...r.kernel.org
Subject: [PATCH] perf/core: Inherit event_caps

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.  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.

Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fc18664f49b0..e28f63ae625b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11560,6 +11560,9 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 
 	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);
 
-- 
2.35.1.265.g69c8d7142f-goog