From 40914de8118eabc711ec0d1735d9372cf20083d7 Mon Sep 17 00:00:00 2001
From: behzad nouri <behzadnouri@gmail.com>
Date: Wed, 4 Aug 2021 11:11:33 -0400
Subject: [PATCH] updates cluster-slots with root-bank instead of root-slot +
 bank-forks

ClusterSlots::update is taking both root-slot and bank-forks only to
later lookup root-bank from bank-forks, which is redundant. Also
potentially by the time bank-forks is locked to obtain root-bank,
root-slot may have already changed and so be inconsistent with the
root-slot passed in as the argument.
https://github.com/solana-labs/solana/blob/6d95d679c/core/src/cluster_slots.rs#L32-L39
https://github.com/solana-labs/solana/blob/6d95d679c/core/src/cluster_slots.rs#L122
---
 core/src/cluster_slots.rs         | 16 +++++-----------
 core/src/cluster_slots_service.rs |  4 ++--
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/core/src/cluster_slots.rs b/core/src/cluster_slots.rs
index 3984f97111..9f6d893866 100644
--- a/core/src/cluster_slots.rs
+++ b/core/src/cluster_slots.rs
@@ -3,7 +3,7 @@ use {
     solana_gossip::{
         cluster_info::ClusterInfo, contact_info::ContactInfo, crds::Cursor, epoch_slots::EpochSlots,
     },
-    solana_runtime::{bank_forks::BankForks, epoch_stakes::NodeIdToVoteAccounts},
+    solana_runtime::{bank::Bank, epoch_stakes::NodeIdToVoteAccounts},
     solana_sdk::{clock::Slot, pubkey::Pubkey},
     std::{
         collections::{BTreeMap, HashMap},
@@ -30,18 +30,13 @@ impl ClusterSlots {
         self.cluster_slots.read().unwrap().get(&slot).cloned()
     }
 
-    pub(crate) fn update(
-        &self,
-        root: Slot,
-        cluster_info: &ClusterInfo,
-        bank_forks: &RwLock<BankForks>,
-    ) {
-        self.update_peers(bank_forks);
+    pub(crate) fn update(&self, root_bank: &Bank, cluster_info: &ClusterInfo) {
+        self.update_peers(root_bank);
         let epoch_slots = {
             let mut cursor = self.cursor.lock().unwrap();
             cluster_info.get_epoch_slots(&mut cursor)
         };
-        self.update_internal(root, epoch_slots);
+        self.update_internal(root_bank.slot(), epoch_slots);
     }
 
     fn update_internal(&self, root: Slot, epoch_slots_list: Vec<EpochSlots>) {
@@ -114,8 +109,7 @@ impl ClusterSlots {
         slot_pubkeys.write().unwrap().insert(node_id, balance);
     }
 
-    fn update_peers(&self, bank_forks: &RwLock<BankForks>) {
-        let root_bank = bank_forks.read().unwrap().root_bank();
+    fn update_peers(&self, root_bank: &Bank) {
         let root_epoch = root_bank.epoch();
         let my_epoch = *self.epoch.read().unwrap();
 
diff --git a/core/src/cluster_slots_service.rs b/core/src/cluster_slots_service.rs
index 09a3042011..251ac39999 100644
--- a/core/src/cluster_slots_service.rs
+++ b/core/src/cluster_slots_service.rs
@@ -91,7 +91,6 @@ impl ClusterSlotsService {
                     break;
                 }
             };
-            let new_root = bank_forks.read().unwrap().root();
             let mut lowest_slot_elapsed = Measure::start("lowest_slot_elapsed");
             let lowest_slot = blockstore.lowest_slot();
             Self::update_lowest_slot(lowest_slot, &cluster_info);
@@ -105,7 +104,8 @@ impl ClusterSlotsService {
                     &cluster_info,
                 );
             }
-            cluster_slots.update(new_root, &cluster_info, &bank_forks);
+            let root_bank = bank_forks.read().unwrap().root_bank();
+            cluster_slots.update(&root_bank, &cluster_info);
             process_cluster_slots_updates_elapsed.stop();
 
             cluster_slots_service_timing.update(