From 445e6668c2e309b430b8f74ccfcb9a1feda30397 Mon Sep 17 00:00:00 2001
From: carllin <wumu727@gmail.com>
Date: Wed, 6 May 2020 11:44:49 -0700
Subject: [PATCH] Fix (#9896)

Co-authored-by: Carl <carl@solana.com>
---
 core/src/replay_stage.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/core/src/replay_stage.rs b/core/src/replay_stage.rs
index 226fd0c904..08ad1615fa 100644
--- a/core/src/replay_stage.rs
+++ b/core/src/replay_stage.rs
@@ -496,10 +496,14 @@ impl ReplayStage {
         bank_forks: &RwLock<BankForks>,
     ) {
         error!("purging slot {}", duplicate_slot);
-        let empty = HashSet::new();
-        let slot_descendants = descendants.get(&duplicate_slot).unwrap_or(&empty);
+        let slot_descendants = descendants.get(&duplicate_slot);
+        if slot_descendants.is_none() {
+            // Root has already moved past this slot, no need to purge it
+            return;
+        }
 
         for d in slot_descendants
+            .unwrap()
             .iter()
             .chain(std::iter::once(&duplicate_slot))
         {