linux-kernel - [tip: perf/urgent] perf/core: Inherit event

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Message-ID: <164914734824.389.11482584782909269521.tip-bot2@tip-bot2>
Date:   Tue, 05 Apr 2022 08:29:08 -0000
From:   "tip-bot2 for Namhyung Kim" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Namhyung Kim <namhyung@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        <stable@...r.kernel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/core: Inherit event_caps

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     e3265a4386428d3d157d9565bb520aabff8b4bf0
Gitweb:        https://git.kernel.org/tip/e3265a4386428d3d157d9565bb520aabff8b4bf0
Author:        Namhyung Kim <namhyung@...nel.org>
AuthorDate:    Mon, 28 Mar 2022 13:01:12 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 05 Apr 2022 09:59:44 +02:00

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 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
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cfde994..3980efc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11635,6 +11635,9 @@ 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);