Fix freeze and register_tick race (#6799)

* Fix freeze and register_tick race

* Add test

runtime/src/bank.rs

@@ -795,12 +795,13 @@ impl Bank {
         // TODO: put this assert back in
         // assert!(!self.is_frozen());
         inc_new_counter_debug!("bank-register_tick-registered", 1);
+        // Grab blockhash lock before incrementing tick height so that replay stage does
+        // not attempt to freeze after observing the last tick and before blockhash is
+        // updated
+        let mut w_blockhash_queue = self.blockhash_queue.write().unwrap();
         let current_tick_height = self.tick_height.fetch_add(1, Ordering::Relaxed) as u64;
         if self.is_block_boundary(current_tick_height + 1) {
-            self.blockhash_queue
-                .write()
-                .unwrap()
-                .register_hash(hash, &self.fee_calculator);
+            w_blockhash_queue.register_hash(hash, &self.fee_calculator);
         }
     }
 

runtime/tests/bank.rs

@@ -0,0 +1,41 @@
+use solana_runtime::bank::Bank;
+use solana_sdk::genesis_block::create_genesis_block;
+use solana_sdk::hash::hash;
+use solana_sdk::pubkey::Pubkey;
+use std::sync::Arc;
+use std::thread::Builder;
+
+#[test]
+fn test_race_register_tick_freeze() {
+    solana_logger::setup();
+
+    let (mut genesis_block, _) = create_genesis_block(50);
+    genesis_block.ticks_per_slot = 1;
+    let p = Pubkey::new_rand();
+    let hash = hash(p.as_ref());
+
+    for _ in 0..1000 {
+        let bank0 = Arc::new(Bank::new(&genesis_block));
+        let bank0_ = bank0.clone();
+        let freeze_thread = Builder::new()
+            .name("freeze".to_string())
+            .spawn(move || loop {
+                if bank0_.tick_height() == bank0_.max_tick_height() {
+                    assert_eq!(bank0_.last_blockhash(), hash);
+                    break;
+                }
+            })
+            .unwrap();
+
+        let bank0_ = bank0.clone();
+        let register_tick_thread = Builder::new()
+            .name("register_tick".to_string())
+            .spawn(move || {
+                bank0_.register_tick(&hash);
+            })
+            .unwrap();
+
+        register_tick_thread.join().unwrap();
+        freeze_thread.join().unwrap();
+    }
+}