linux-kernel - [PATCH AUTOSEL for 4.14 17/51] perf/core: Fix __perf_read_group

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Date:   Wed, 22 Nov 2017 22:25:40 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...nel.org>, alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.14 17/51] perf/core: Fix __perf_read_group_add()
 locking

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit a9cd8194e1e6bd09619954721dfaf0f94fe2003e ]

Event timestamps are serialized using ctx->lock, make sure to hold it
over reading all values.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 10cdb9c26b5d..4f1d4bfc607a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4433,6 +4433,8 @@ static int __perf_read_group_add(struct perf_event *leader,
 	if (ret)
 		return ret;
 
+	raw_spin_lock_irqsave(&ctx->lock, flags);
+
 	/*
 	 * Since we co-schedule groups, {enabled,running} times of siblings
 	 * will be identical to those of the leader, so we only publish one
@@ -4455,8 +4457,6 @@ static int __perf_read_group_add(struct perf_event *leader,
 	if (read_format & PERF_FORMAT_ID)
 		values[n++] = primary_event_id(leader);
 
-	raw_spin_lock_irqsave(&ctx->lock, flags);
-
 	list_for_each_entry(sub, &leader->sibling_list, group_entry) {
 		values[n++] += perf_event_count(sub);
 		if (read_format & PERF_FORMAT_ID)
-- 
2.11.0