From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 5 Sep 2017 13:38:24 +0200
Subject: perf/core: Fix __perf_read_group_add() locking
Git-commit: a9cd8194e1e6bd09619954721dfaf0f94fe2003e
Patch-mainline: v4.15-rc1
References: git-fixes (dependent patch)

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Tony Jones <tonyj@suse.de>
---
 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 5fae98626b15..0f34f2a47eb6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4453,6 +4453,8 @@ 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
@@ -4475,8 +4477,6 @@ 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)