Fix moveRegularItemOnEviction function

Author: vinser52

cachelib/allocator/CacheAllocator-inl.h

@@ -1246,35 +1246,17 @@ CacheAllocator<CacheTrait>::moveRegularItemOnEviction(
   // make sure that no other thread removed it, and only then replaces it.
   if (!replaceInMMContainer(oldItemPtr, *newItemHdl)) {
     accessContainer_->remove(*newItemHdl);
-    return {};
+    return acquire(&oldItem);
   }
 
   // Replacing into the MM container was successful, but someone could have
   // called insertOrReplace() or remove() before or after the
   // replaceInMMContainer() operation, which would invalidate newItemHdl.
   if (!newItemHdl->isAccessible()) {
     removeFromMMContainer(*newItemHdl);
-    return {};
+    return acquire(&oldItem);
   }
 
-  // no one can add or remove chained items at this point
-  if (oldItem.hasChainedItem()) {
-    // safe to acquire handle for a moving Item
-    auto oldHandle = acquire(&oldItem);
-    XDCHECK_EQ(1u, oldHandle->getRefCount()) << oldHandle->toString();
-    XDCHECK(!newItemHdl->hasChainedItem()) << newItemHdl->toString();
-    try {
-      auto l = chainedItemLocks_.lockExclusive(oldItem.getKey());
-      transferChainLocked(oldHandle, newItemHdl);
-    } catch (const std::exception& e) {
-      // this should never happen because we drained all the handles.
-      XLOGF(DFATAL, "{}", e.what());
-      throw;
-    }
-
-    XDCHECK(!oldItem.hasChainedItem());
-    XDCHECK(newItemHdl->hasChainedItem());
-  }
   newItemHdl.unmarkNascent();
   resHdl = std::move(newItemHdl); // guard will assign it to ctx under lock
   return acquire(&oldItem);

cachelib/allocator/CacheAllocator.h

@@ -1281,8 +1281,8 @@ class CacheAllocator : public CacheBase {
   // @param oldItem     Reference to the item being moved
   // @param newItemHdl  Reference to the handle of the new item being moved into
   //
-  // @return true  If the move was completed, and the containers were updated
-  //               successfully.
+  // @return       the handle to the oldItem if the move was completed
+  //               and the oldItem can be recycled.
   template <typename ItemPtr>
   ItemHandle moveRegularItemOnEviction(ItemPtr& oldItem, ItemHandle& newItemHdl);