From 2ae342b1b7a2af38332c3d41e9b9e8afa93249f0 Mon Sep 17 00:00:00 2001
From: Nick Cabatoff <ncabatoff@hashicorp.com>
Date: Mon, 16 Jan 2023 13:49:11 -0500
Subject: [PATCH] Speculative fix for a panic that might arise during raft
 teardown (#18704)

---
 changelog/18704.txt             | 3 +++
 physical/raft/raft_autopilot.go | 7 +++++++
 2 files changed, 10 insertions(+)
 create mode 100644 changelog/18704.txt

diff --git a/changelog/18704.txt b/changelog/18704.txt
new file mode 100644
index 000000000000..bc76db9ba923
--- /dev/null
+++ b/changelog/18704.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+storage/raft: Fix race with follower heartbeat tracker during teardown.
+```
\ No newline at end of file
diff --git a/physical/raft/raft_autopilot.go b/physical/raft/raft_autopilot.go
index 5596bbf4255f..1c000dc04824 100644
--- a/physical/raft/raft_autopilot.go
+++ b/physical/raft/raft_autopilot.go
@@ -551,6 +551,13 @@ func (b *RaftBackend) startFollowerHeartbeatTracker() {
 	}
 	for range tickerCh {
 		b.l.RLock()
+		if b.raft == nil {
+			// We could be racing with teardown, which will stop the ticker
+			// but that doesn't guarantee that we won't reach this line with a nil
+			// b.raft.
+			b.l.RUnlock()
+			return
+		}
 		b.followerStates.l.RLock()
 		myAppliedIndex := b.raft.AppliedIndex()
 		for peerID, state := range b.followerStates.followers {