kvserver: rlock replica mu when reading follower state info

Goroutines can mutate the Raft node state without acquiring raftMu,
however must acquire replica mu.

Acquire a read lock on replica mu when reading the tracker progress
state from the raw node in `FollowerStateRaftMuLocked` to prevent races.

Part of: #130187
Release note: None

pkg/kv/kvserver/kvflowcontrol/replica_rac2/raft_node.go

@@ -19,12 +19,13 @@ import (
 )
 
 type raftNodeForRACv2 struct {
+	Replica
 	*raft.RawNode
 }
 
 // NewRaftNode creates a RaftNode implementation from the given RawNode.
-func NewRaftNode(rn *raft.RawNode) RaftNode {
-	return raftNodeForRACv2{RawNode: rn}
+func NewRaftNode(rn *raft.RawNode, r Replica) RaftNode {
+	return raftNodeForRACv2{RawNode: rn, Replica: r}
 }
 
 func (rn raftNodeForRACv2) TermLocked() uint64 {
@@ -47,6 +48,9 @@ func (rn raftNodeForRACv2) FollowerStateRaftMuLocked(
 	replicaID roachpb.ReplicaID,
 ) rac2.FollowerStateInfo {
 	// TODO(pav-kv): this is a temporary implementation.
+	rn.MuRLock()
+	defer rn.MuRUnlock()
+
 	status := rn.Status()
 	if progress, ok := status.Progress[raftpb.PeerID(replicaID)]; ok {
 		return rac2.FollowerStateInfo{

pkg/kv/kvserver/replica_init.go

@@ -323,7 +323,7 @@ func (r *Replica) initRaftGroupRaftMuLockedReplicaMuLocked() error {
 		return err
 	}
 	r.mu.internalRaftGroup = rg
-	r.flowControlV2.InitRaftLocked(ctx, replica_rac2.NewRaftNode(rg))
+	r.flowControlV2.InitRaftLocked(ctx, replica_rac2.NewRaftNode(rg, (*replicaForRACv2)(r)))
 	return nil
 }