From 9bd3c365ccd2c7c312d72114cd564e600255097b Mon Sep 17 00:00:00 2001
From: Herman Zhu <zhuhuijunzhj@gmail.com>
Date: Tue, 9 Jul 2024 17:12:51 +0800
Subject: [PATCH] perf: fix panic when CPU is offline

Commit 75bce381 ("perf: opportunistically check all rings for data") introduced a panic on systems where not all CPUs are online. Fix this by skipping nil rings.

Signed-off-by: zhuhuijun <zhuhuijunzhj@gmail.com>
---
 perf/reader.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/perf/reader.go b/perf/reader.go
index ee557e449..79c4f502d 100644
--- a/perf/reader.go
+++ b/perf/reader.go
@@ -386,6 +386,11 @@ func (pr *Reader) ReadInto(rec *Record) error {
 			// Waking up userspace is expensive, make the most of it by checking
 			// all rings.
 			for _, ring := range pr.rings {
+				// Skip rings that are not currently enabled.
+				if ring == nil {
+					continue
+				}
+
 				ring.loadHead()
 				pr.epollRings = append(pr.epollRings, ring)
 			}