v1.18: fix: send votes to the immediate next leader (backport of #2607)

core/src/next_leader.rs

@@ -1,4 +1,5 @@
 use {
+    itertools::Itertools,
     solana_gossip::{
         cluster_info::ClusterInfo, legacy_contact_info::LegacyContactInfo as ContactInfo,
     },
@@ -7,6 +8,33 @@ use {
     std::{net::SocketAddr, sync::RwLock},
 };
 
+/// Returns a list of tpu vote sockets for the leaders of the next N fanout
+/// slots. Leaders and sockets are deduped.
+pub(crate) fn upcoming_leader_tpu_vote_sockets(
+    cluster_info: &ClusterInfo,
+    poh_recorder: &RwLock<PohRecorder>,
+    fanout_slots: u64,
+) -> Vec<SocketAddr> {
+    let upcoming_leaders = {
+        let poh_recorder = poh_recorder.read().unwrap();
+        (1..=fanout_slots)
+            .filter_map(|n_slots| poh_recorder.leader_after_n_slots(n_slots))
+            .collect_vec()
+    };
+
+    upcoming_leaders
+        .into_iter()
+        .dedup()
+        .filter_map(|leader_pubkey| {
+            cluster_info
+                .lookup_contact_info(&leader_pubkey, ContactInfo::tpu_vote)?
+                .ok()
+        })
+        // dedup again since leaders could potentially share the same tpu vote socket
+        .dedup()
+        .collect()
+}
+
 pub(crate) fn next_leader_tpu_vote(
     cluster_info: &ClusterInfo,
     poh_recorder: &RwLock<PohRecorder>,

core/src/voting_service.rs

@@ -1,13 +1,16 @@
 use {
     crate::{
         consensus::tower_storage::{SavedTowerVersions, TowerStorage},
-        next_leader::next_leader_tpu_vote,
+        next_leader::upcoming_leader_tpu_vote_sockets,
     },
     crossbeam_channel::Receiver,
     solana_gossip::cluster_info::ClusterInfo,
     solana_measure::measure::Measure,
     solana_poh::poh_recorder::PohRecorder,
-    solana_sdk::{clock::Slot, transaction::Transaction},
+    solana_sdk::{
+        clock::{Slot, FORWARD_TRANSACTIONS_TO_LEADER_AT_SLOT_OFFSET},
+        transaction::Transaction,
+    },
     std::{
         sync::{Arc, RwLock},
         thread::{self, Builder, JoinHandle},
@@ -78,12 +81,25 @@ impl VotingService {
             inc_new_counter_info!("tower_save-ms", measure.as_ms() as usize);
         }
 
-        let _ = cluster_info.send_transaction(
-            vote_op.tx(),
-            next_leader_tpu_vote(cluster_info, poh_recorder)
-                .map(|(_pubkey, target_addr)| target_addr),
+        // Attempt to send our vote transaction to the leaders for the next few slots
+        const UPCOMING_LEADER_FANOUT_SLOTS: u64 = FORWARD_TRANSACTIONS_TO_LEADER_AT_SLOT_OFFSET;
+        #[cfg(test)]
+        static_assertions::const_assert_eq!(UPCOMING_LEADER_FANOUT_SLOTS, 2);
+        let upcoming_leader_sockets = upcoming_leader_tpu_vote_sockets(
+            cluster_info,
+            poh_recorder,
+            UPCOMING_LEADER_FANOUT_SLOTS,
         );
 
+        if !upcoming_leader_sockets.is_empty() {
+            for tpu_vote_socket in upcoming_leader_sockets {
+                let _ = cluster_info.send_transaction(vote_op.tx(), Some(tpu_vote_socket));
+            }
+        } else {
+            // Send to our own tpu vote socket if we cannot find a leader to send to
+            let _ = cluster_info.send_transaction(vote_op.tx(), None);
+        }
+
         match vote_op {
             VoteOp::PushVote {
                 tx, tower_slots, ..