Allow voting on empty banks (#6719)

* Allow votes on empty banks

* Remove making first bank is_delta true, no longer necessary for idling

* Remove votable from ledger tool

core/src/replay_stage.rs

@@ -492,6 +492,9 @@ impl ReplayStage {
     where
         T: 'static + KeypairUtil + Send + Sync,
     {
+        if bank.is_empty() {
+            inc_new_counter_info!("replay_stage-voted_empty_bank", 1);
+        }
         trace!("handle votable bank {}", bank.slot());
         let (vote, tower_index) = tower.new_vote_from_bank(bank, vote_account);
         if let Some(new_root) = tower.record_bank_vote(vote) {
@@ -651,11 +654,6 @@ impl ReplayStage {
         trace!("frozen_banks {}", frozen_banks.len());
         let mut votable: Vec<(u128, Arc<Bank>, HashMap<u64, StakeLockout>, u64)> = frozen_banks
             .values()
-            .filter(|b| {
-                let is_votable = b.is_votable();
-                trace!("bank is votable: {} {}", b.slot(), is_votable);
-                is_votable
-            })
             .filter(|b| {
                 let has_voted = tower.has_voted(b.slot());
                 trace!("bank has_voted: {} {}", b.slot(), has_voted);

ledger-tool/src/main.rs

@@ -149,7 +149,7 @@ fn graph_forks(
                         "".to_string()
                     },
                     if first { "filled," } else { "" },
-                    if !bank.is_votable() { "dotted," } else { "" }
+                    ""
                 ));
                 styled_slots.insert(bank.slot());
             }

local_cluster/src/tests/local_cluster.rs

@@ -7,8 +7,8 @@ use log::*;
 use serial_test_derive::serial;
 use solana_client::thin_client::create_client;
 use solana_core::{
-    broadcast_stage::BroadcastStageType, gossip_service::discover_cluster,
-    validator::ValidatorConfig,
+    broadcast_stage::BroadcastStageType, consensus::VOTE_THRESHOLD_DEPTH,
+    gossip_service::discover_cluster, validator::ValidatorConfig,
 };
 use solana_ledger::{bank_forks::SnapshotConfig, blocktree::Blocktree, snapshot_utils};
 use solana_runtime::accounts_db::AccountsDB;
@@ -626,7 +626,47 @@ fn test_faulty_node(faulty_node_type: BroadcastStageType) {
 }
 
 #[test]
-#[serial]
+// Test that when a leader is leader for banks B_i..B_{i+n}, and B_i is not
+// votable, then B_{i+1} still chains to B_i
+fn test_no_voting() {
+    solana_logger::setup();
+    let mut validator_config = ValidatorConfig::default();
+    validator_config.rpc_config.enable_validator_exit = true;
+    validator_config.voting_disabled = true;
+    let config = ClusterConfig {
+        cluster_lamports: 10_000,
+        node_stakes: vec![100],
+        validator_configs: vec![validator_config.clone()],
+        ..ClusterConfig::default()
+    };
+    let mut cluster = LocalCluster::new(&config);
+    let client = cluster
+        .get_validator_client(&cluster.entry_point_info.id)
+        .unwrap();
+    loop {
+        let last_slot = client.get_slot().expect("Couldn't get slot");
+        if last_slot > 4 * VOTE_THRESHOLD_DEPTH as u64 {
+            break;
+        }
+        sleep(Duration::from_secs(1));
+    }
+
+    cluster.close_preserve_ledgers();
+    let leader_pubkey = cluster.entry_point_info.id;
+    let ledger_path = cluster.validator_infos[&leader_pubkey]
+        .info
+        .ledger_path
+        .clone();
+    let ledger = Blocktree::open(&ledger_path).unwrap();
+    for i in 0..2 * VOTE_THRESHOLD_DEPTH {
+        let meta = ledger.meta(i as u64).unwrap().unwrap();
+        let parent = meta.parent_slot;
+        let expected_parent = i.saturating_sub(1);
+        assert_eq!(parent, expected_parent as u64);
+    }
+}
+
+#[test]
 fn test_repairman_catchup() {
     solana_logger::setup();
     error!("test_repairman_catchup");

runtime/src/bank.rs

@@ -693,9 +693,6 @@ impl Bank {
         //  / ticks/slot
             / self.ticks_per_slot as f64;
 
-        // make bank 0 votable
-        self.is_delta.store(true, Ordering::Relaxed);
-
         self.epoch_schedule = genesis_block.epoch_schedule;
 
         self.inflation = genesis_block.inflation;
@@ -1529,8 +1526,8 @@ impl Bank {
         self.epoch_schedule.get_epoch_and_slot_index(slot)
     }
 
-    pub fn is_votable(&self) -> bool {
-        self.is_delta.load(Ordering::Relaxed) && self.tick_height() == self.max_tick_height
+    pub fn is_empty(&self) -> bool {
+        !self.is_delta.load(Ordering::Relaxed)
     }
 
     /// Add an instruction processor to intercept instructions before the dynamic loader.
@@ -1633,7 +1630,6 @@ mod tests {
         clock::DEFAULT_TICKS_PER_SLOT,
         epoch_schedule::MINIMUM_SLOTS_PER_EPOCH,
         genesis_block::create_genesis_block,
-        hash,
         instruction::InstructionError,
         message::{Message, MessageHeader},
         poh_config::PohConfig,
@@ -2935,38 +2931,19 @@ mod tests {
     }
 
     #[test]
-    fn test_is_votable() {
-        // test normal case
+    fn test_is_empty() {
         let (genesis_block, mint_keypair) = create_genesis_block(500);
-        let bank = Arc::new(Bank::new(&genesis_block));
+        let bank0 = Arc::new(Bank::new(&genesis_block));
         let key1 = Keypair::new();
-        assert_eq!(bank.is_votable(), false);
 
-        // Set is_delta to true
+        // The zeroth bank is empty becasue there are no transactions
+        assert_eq!(bank0.is_empty(), true);
+
+        // Set is_delta to true, bank is no longer empty
         let tx_transfer_mint_to_1 =
             system_transaction::transfer(&mint_keypair, &key1.pubkey(), 1, genesis_block.hash());
-        assert_eq!(bank.process_transaction(&tx_transfer_mint_to_1), Ok(()));
-        assert_eq!(bank.is_votable(), false);
-
-        // Register enough ticks to hit max tick height
-        for i in 0..genesis_block.ticks_per_slot {
-            bank.register_tick(&hash::hash(format!("hello world {}", i).as_bytes()));
-        }
-
-        assert_eq!(bank.is_votable(), true);
-
-        // test empty bank with ticks
-        let (genesis_block, _mint_keypair) = create_genesis_block(500);
-        // make an empty bank at slot 1
-        let bank = new_from_parent(&Arc::new(Bank::new(&genesis_block)));
-        assert_eq!(bank.is_votable(), false);
-
-        // Register enough ticks to hit max tick height
-        for i in 0..genesis_block.ticks_per_slot {
-            bank.register_tick(&hash::hash(format!("hello world {}", i).as_bytes()));
-        }
-        // empty banks aren't votable even at max tick height
-        assert_eq!(bank.is_votable(), false);
+        assert_eq!(bank0.process_transaction(&tx_transfer_mint_to_1), Ok(()));
+        assert_eq!(bank0.is_empty(), false);
     }
 
     #[test]
@@ -3068,16 +3045,6 @@ mod tests {
         assert_eq!(vote_accounts.len(), 1);
     }
 
-    #[test]
-    fn test_bank_0_votable() {
-        let (genesis_block, _) = create_genesis_block(500);
-        let bank = Arc::new(Bank::new(&genesis_block));
-        //set tick height to max
-        let max_tick_height = (bank.slot + 1) * bank.ticks_per_slot;
-        bank.tick_height.store(max_tick_height, Ordering::Relaxed);
-        assert!(bank.is_votable());
-    }
-
     #[test]
     fn test_bank_fees_account() {
         let (mut genesis_block, _) = create_genesis_block(500);