[zero] fix missing hook removal

colossalai/zero/low_level/low_level_strategy.py

@@ -1,4 +1,5 @@
 # this code is inspired by the DeepSpeed library and implemented with our own design from scratch
+import weakref
 from abc import ABC, abstractmethod
 from copy import deepcopy
 from functools import partial
@@ -94,20 +95,27 @@ def __init__(
         # reduction hook is only used if overlapping communication
         # or stage 2 is used
         # if it is stage 1 without overlapping, no hook will be attached
+        self.grad_handles = []
         if self._overlap_communication or self._partition_grad:
             # we iterate over the working params
             # on each param, we register a hook to its AccumulateGrad object
             param_group = self.working_param_group
             for param in param_group:
                 if param.requires_grad:
+                    self_weak_proxy = weakref.proxy(self)
+                    param_weak_proxy = weakref.proxy(param)
 
-                    def _grad_handler(grad, param):
+                    def _grad_handler(grad):
                         # if run with no_sync context, would not sync grad when backward
-                        if self.require_grad_sync:
-                            self._add_to_bucket(param)
+                        if self_weak_proxy.require_grad_sync:
+                            self_weak_proxy._add_to_bucket(param_weak_proxy)
                         return grad
 
-                    param.register_hook(partial(_grad_handler, param=param))
+                    self.grad_handles.append(param.register_post_accumulate_grad_hook(partial(_grad_handler)))
+
+    def __del__(self):
+        for handle in self.grad_handles:
+            handle.remove()
 
     def _create_master_param_current_rank(self, param_list):
         # split each param evenly by world size