linux-kernel - [PATCH 02/10] perf: Fix leader for removed sibling event in perf_group

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Date:   Thu, 24 Aug 2017 18:27:29 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <andi@...stfloor.org>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH 02/10] perf: Fix leader for removed sibling event in perf_group_detach

Mark reported warning in x86_perf_event_update caused
by reading unscheduled leader of an event that was
already removed from the group.

As he pointed out we don't properly reset event's leader
once it's been detached from the group and he posted the
attached fix.

[1] https://marc.info/?l=linux-kernel&m=150238662928203&w=2

Originally-From: Mark Rutland <mark.rutland@....com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/events/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d704e23914bf..30e30e94ea32 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1727,6 +1727,7 @@ static void perf_group_detach(struct perf_event *event)
 	if (event->group_leader != event) {
 		list_del_init(&event->group_entry);
 		event->group_leader->nr_siblings--;
+		event->group_leader = event;
 		goto out;
 	}
 
-- 
2.9.5