Fix crash after flush cache (#12107)

Co-authored-by: fzyzcjy <5236035+fzyzcjy@users.noreply.github.com>

python/sglang/srt/managers/scheduler.py

@@ -2305,13 +2305,30 @@ class Scheduler(
             if_success = False
         return ClearHiCacheReqOutput(success=if_success)
 
-    def flush_cache(self):
-        """Flush the memory pool and cache."""
-        if (
+    def _is_no_request(self):
+        no_request = (
             len(self.waiting_queue) == 0
             and self.running_batch.is_empty()
+            and (self.last_batch is None or self.last_batch.is_empty())
+            and (self.cur_batch is None or self.cur_batch.is_empty())
+            and (not self.enable_overlap or len(self.result_queue) == 0)
             and (self.pp_size == 1 or all(x.is_empty() for x in self.running_mbs))
-        ):
+        )
+        if self.disaggregation_mode == DisaggregationMode.PREFILL:
+            no_request &= (
+                len(self.disagg_prefill_bootstrap_queue.queue) == 0
+                and len(self.disagg_prefill_inflight_queue) == 0
+            )
+        if self.disaggregation_mode == DisaggregationMode.DECODE:
+            no_request &= (
+                len(self.disagg_decode_prealloc_queue.queue) == 0
+                and len(self.disagg_decode_transfer_queue.queue) == 0
+            )
+        return no_request
+
+    def flush_cache(self):
+        """Flush the memory pool and cache."""
+        if self._is_no_request():
             self.cur_batch = None
             self.last_batch = None
             self.tree_cache.reset()

python/sglang/srt/mem_cache/radix_cache.py

@@ -533,6 +533,10 @@ class RadixCache(BasePrefixCache):
                 self.protected_size_ -= len(node.key)
                 delta += len(node.key)
             node.lock_ref -= 1
+            if node.parent is None:
+                assert (
+                    node is self.root_node
+                ), f"This request holds the node from another tree"
             node = node.parent
         return delta