From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sun, 20 Jun 2021 00:08:13 -0700
Subject: [PATCH] Do not allow ticket level changes when updating chunk ticking
 state

This WILL cause state corruption if it happens. So, don't
allow it.

diff --git a/src/main/java/net/minecraft/server/level/ChunkHolder.java b/src/main/java/net/minecraft/server/level/ChunkHolder.java
index b6445778a023531774784f1a6e569849dda4c8ce..c70e1018c5e5b65911ee430be123e38f03666df2 100644
--- a/src/main/java/net/minecraft/server/level/ChunkHolder.java
+++ b/src/main/java/net/minecraft/server/level/ChunkHolder.java
@@ -418,7 +418,13 @@ public class ChunkHolder {
         CompletableFuture<Void> completablefuture1 = new CompletableFuture();
 
         completablefuture1.thenRunAsync(() -> {
+            // Paper start - do not allow ticket level changes
+            boolean unloadingBefore = this.chunkMap.unloadingPlayerChunk;
+            this.chunkMap.unloadingPlayerChunk = true;
+            try {
+            // Paper end  - do not allow ticket level changes
             playerchunkmap.onFullChunkStatusChange(this.pos, playerchunk_state);
+            } finally { this.chunkMap.unloadingPlayerChunk = unloadingBefore; } // Paper - do not allow ticket level changes
         }, executor);
         this.pendingFullStateConfirmation = completablefuture1;
         completablefuture.thenAccept((either) -> {
@@ -435,7 +441,12 @@ public class ChunkHolder {
 
     private void demoteFullChunk(ChunkMap playerchunkmap, ChunkHolder.FullChunkStatus playerchunk_state) {
         this.pendingFullStateConfirmation.cancel(false);
+        // Paper start - do not allow ticket level changes
+        boolean unloadingBefore = this.chunkMap.unloadingPlayerChunk;
+        this.chunkMap.unloadingPlayerChunk = true;
+        try { // Paper end  - do not allow ticket level changes
         playerchunkmap.onFullChunkStatusChange(this.pos, playerchunk_state);
+        } finally { this.chunkMap.unloadingPlayerChunk = unloadingBefore; } // Paper - do not allow ticket level changes
     }
 
     protected long updateCount; // Paper - correctly handle recursion