fix mamba cache leak when adder fails to add a matched req. (#21404)

python/sglang/srt/managers/scheduler.py

@@ -2416,6 +2416,13 @@ class Scheduler(
                         ) > 0 or (not self.running_batch.is_empty())
                     else:
                         self.running_batch.batch_is_full = True
+                # revert matched mamba idx to avoid memory leak, if req is not added
+                added = len(adder.can_run_list) > 0 and req is adder.can_run_list[-1]
+                if not added and req.mamba_pool_idx is not None:
+                    self.tree_cache.req_to_token_pool.mamba_pool.free(
+                        req.mamba_pool_idx.unsqueeze(-1)
+                    )
+                    req.mamba_pool_idx = None
                 break
 
         # Update waiting queue