Fix swa chunk req deferred (#24318)

python/sglang/srt/managers/scheduler.py

@@ -1080,6 +1080,15 @@ class Scheduler(
         elif self.chunked_prefill_size is not None and self.chunked_prefill_size <= 0:
             self.chunked_prefill_size = None
         self.chunked_req = None
+        # Tracks whether the current self.chunked_req was actually scheduled
+        # into last iteration's batch (i.e., in can_run_list -> got a fresh
+        # req_pool_idx from prepare_for_extend). Used to gate the
+        # stash_chunked_request call at the top of get_next_batch_to_run:
+        # if add_chunked_req early-returned under hybrid-SWA pressure,
+        # the req_pool_idx was already freed and fill_ids was reset by
+        # init_next_round_input, so running stash would double-free and
+        # corrupt prefix_indices.
+        self._chunked_req_scheduled_last_iter = False
         self.is_mixed_chunk = (
             self.chunked_prefill_size is not None
             and self.server_args.enable_mixed_chunk
@@ -2455,7 +2464,9 @@ class Scheduler(
             # Move the chunked request out of the batch so that we can merge
             # only finished requests to running_batch.
             chunked_req_to_exclude.add(self.chunked_req)
-            self.stash_chunked_request(self.chunked_req)
+
+            if self._chunked_req_scheduled_last_iter:
+                self.stash_chunked_request(self.chunked_req)
 
         # HiSparse has its own prefill-to-decode transition; skip last_batch merge.
         if self.enable_hisparse:
@@ -2650,6 +2661,11 @@ class Scheduler(
         if self.chunked_req is not None:
             self.chunked_req.init_next_round_input()
             self.chunked_req = adder.add_chunked_req(self.chunked_req)
+            self._chunked_req_scheduled_last_iter = (
+                self.chunked_req in adder.can_run_list
+            )
+        else:
+            self._chunked_req_scheduled_last_iter = False
 
         if self.enable_lora:
             running_loras = {req.lora_id for req in self.running_batch.reqs}
@@ -2741,6 +2757,9 @@ class Scheduler(
             # Update chunked prefill
             assert self.chunked_req is None
             self.chunked_req = adder.new_chunked_req
+            # new_chunked_req is added to can_run_list by add_one_req,
+            # so it will be scheduled this iter -> stash is needed next iter.
+            self._chunked_req_scheduled_last_iter = True
 
         if self.chunked_req is not None:
             self.chunked_req.is_chunked += 1