From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 5 Sep 2017 13:23:44 +0200
Subject: perf/core: Fix perf_event_read_value() locking
Git-commit: ca0dd44cf37bfe316751e1701439c3ff44beb05c
Patch-mainline: v4.15-rc1
References: git-fixes

perf_event_read_value() is an external accessor, just like
perf_event_{en,dis}able() and should thus use perf_event_ctx_lock().

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>
Fixes: f63a8daa5812 ("perf: Fix event->ctx locking")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Tony Jones <tonyj@suse.de>
---
 kernel/events/core.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 74671e101b92..d636f1d0e2ab 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4398,7 +4398,7 @@ static int perf_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
+static u64 __perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 {
 	struct perf_event *child;
 	u64 total = 0;
@@ -4426,6 +4426,18 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 
 	return total;
 }
+
+u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
+{
+	struct perf_event_context *ctx;
+	u64 count;
+
+	ctx = perf_event_ctx_lock(event);
+	count = __perf_event_read_value(event, enabled, running);
+	perf_event_ctx_unlock(event, ctx);
+
+	return count;
+}
 EXPORT_SYMBOL_GPL(perf_event_read_value);
 
 static int __perf_read_group_add(struct perf_event *leader,
@@ -4528,7 +4540,7 @@ static int perf_read_one(struct perf_event *event,
 	u64 values[4];
 	int n = 0;
 
-	values[n++] = perf_event_read_value(event, &enabled, &running);
+	values[n++] = __perf_event_read_value(event, &enabled, &running);
 	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
 		values[n++] = enabled;
 	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)