[BugFix][HiMamba] Fix host-protected node deletion in HiMamba tombstone del (#23696)

Co-authored-by: diemchai <diemchai@tencent.com>
Co-authored-by: Zhangheng <hzh0425@apache.org>

test/registered/unit/mem_cache/test_mamba_unittest.py

@@ -13,7 +13,8 @@ from sglang.srt.mem_cache.base_prefix_cache import (
 )
 from sglang.srt.mem_cache.cache_init_params import CacheInitParams
 from sglang.srt.mem_cache.common import available_and_evictable_str
-from sglang.srt.mem_cache.mamba_radix_cache import MambaRadixCache
+from sglang.srt.mem_cache.hi_mamba_radix_cache import HiMambaRadixCache
+from sglang.srt.mem_cache.mamba_radix_cache import LRUList, MambaRadixCache, TreeNode
 from sglang.srt.mem_cache.memory_pool import HybridLinearKVPool, HybridReqToTokenPool
 from sglang.srt.mem_cache.radix_cache import RadixKey
 from sglang.srt.sampling.sampling_params import SamplingParams
@@ -392,6 +393,53 @@ class TestMamba(unittest.TestCase):
 
         return tree, allocator, req_to_token_pool, make_dummy_req
 
+    def test_hi_mamba_tombstone_cleanup_respects_host_ref(self):
+        tree = object.__new__(HiMambaRadixCache)
+        root = TreeNode()
+        parent = TreeNode()
+        deleted = TreeNode()
+
+        root.key = RadixKey([])
+        parent.key = RadixKey([1])
+        deleted.key = RadixKey([2])
+        parent.parent = root
+        deleted.parent = parent
+        parent.value = torch.tensor([1], dtype=torch.int64)
+        parent.protect_host()
+        root.children[parent.key.child_key(1)] = parent
+
+        class RecordingCacheController:
+            def __init__(self):
+                self.device_evictions = []
+                self.host_evictions = []
+
+            def evict_device(self, value):
+                self.device_evictions.append(value)
+
+            def evict_host(self, value):
+                self.host_evictions.append(value)
+
+        tree.root_node = root
+        tree.page_size = 1
+        tree.full_lru_list = LRUList(mamba=False)
+        tree.full_lru_list.insert_mru(parent)
+        tree.cache_controller = RecordingCacheController()
+        tree.full_evictable_size_ = len(parent.value)
+        tree.evictable_full_device_leaves = {parent}
+        tree.evictable_full_host_leaves = set()
+
+        result_node, full_evicted, mamba_evicted = (
+            tree._iteratively_delete_tombstone_leaf(deleted)
+        )
+
+        self.assertIs(result_node, deleted)
+        self.assertEqual(full_evicted, 0)
+        self.assertEqual(mamba_evicted, 0)
+        self.assertIs(root.children[parent.key.child_key(1)], parent)
+        self.assertTrue(tree.full_lru_list.in_list(parent))
+        self.assertEqual(tree.cache_controller.device_evictions, [])
+        self.assertEqual(tree.cache_controller.host_evictions, [])
+
     def test_mamba_pool_cpu_offload(self):
         """MambaPool.get_cpu_copy / load_cpu_copy round-trips conv and temporal state."""
         _, _, req_to_token_pool, _ = self._setup_tree_and_allocator()

test/registered/unit/mem_cache/test_unified_radix_cache_unittest.py

@@ -28,7 +28,10 @@ from sglang.srt.mem_cache.memory_pool import (
 from sglang.srt.mem_cache.radix_cache import RadixKey
 from sglang.srt.mem_cache.swa_memory_pool import SWAKVPool, SWATokenToKVPoolAllocator
 from sglang.srt.mem_cache.unified_cache_components.tree_component import ComponentType
-from sglang.srt.mem_cache.unified_radix_cache import UnifiedRadixCache
+from sglang.srt.mem_cache.unified_radix_cache import (
+    UnifiedRadixCache,
+    UnifiedTreeNode,
+)
 from sglang.srt.sampling.sampling_params import SamplingParams
 from sglang.srt.server_args import (
     ServerArgs,
@@ -871,6 +874,30 @@ class UnifiedRadixCacheSuite:
         )
         tree.sanity_check()
 
+    def test_tombstone_cleanup_respects_locked_parent(self):
+        tree, _, _ = build_fixture(self.cfg)
+        parent = UnifiedTreeNode(self.cfg.components)
+        deleted = UnifiedTreeNode(self.cfg.components)
+
+        parent.key = RadixKey(self._make_seq(1, 1))
+        deleted.key = RadixKey(self._make_seq(1000, 1))
+        parent.parent = tree.root_node
+        deleted.parent = parent
+        parent.component_data[ComponentType.FULL].value = torch.arange(
+            self.cfg.page_size, dtype=torch.int64, device=tree.device
+        )
+        parent.component_data[ComponentType.FULL].lock_ref = 1
+        parent_key = parent.key.child_key(tree.page_size)
+        tree.root_node.children[parent_key] = parent
+
+        tracker = {ct: 0 for ct in tree.tree_components}
+
+        tree._iteratively_delete_tombstone_leaf(deleted, tracker)
+
+        self.assertIn(parent_key, tree.root_node.children)
+        self.assertIs(tree.root_node.children[parent_key], parent)
+        self.assertTrue(all(evicted == 0 for evicted in tracker.values()))
+
     def test_internal_readonly_does_not_modify_tree(self):
         """Verify readonly match does not modify tree structure (no split)."""
         if self.cfg.page_size > 1 or self.cfg.has_mamba or self.cfg.has_swa: