[Fix] Fix _sync_params was removed in torch1.11.0 (#1816)

* fix pt111 dist

* fix val step

mmcv/parallel/distributed.py

@@ -44,8 +44,15 @@ class MMDistributedDataParallel(DistributedDataParallel):
                 'Reducer buckets have been rebuilt in this iteration.',
                 logger='mmcv')
 
-        if getattr(self, 'require_forward_param_sync', True):
-            self._sync_params()
+        if ('parrots' not in TORCH_VERSION
+                and digit_version(TORCH_VERSION) >= digit_version('1.11.0')):
+            if self._check_sync_bufs_pre_fwd():
+                self._sync_buffers()
+        else:
+            if (getattr(self, 'require_forward_param_sync', False)
+                    and self.require_forward_param_sync):
+                self._sync_params()
+
         if self.device_ids:
             inputs, kwargs = self.scatter(inputs, kwargs, self.device_ids)
             if len(self.device_ids) == 1:
@@ -57,8 +64,14 @@ class MMDistributedDataParallel(DistributedDataParallel):
         else:
             output = self.module.train_step(*inputs, **kwargs)
 
-        if torch.is_grad_enabled() and getattr(
-                self, 'require_backward_grad_sync', True):
+        if ('parrots' not in TORCH_VERSION
+                and digit_version(TORCH_VERSION) >= digit_version('1.11.0')):
+            if self._check_sync_bufs_post_fwd():
+                self._sync_buffers()
+
+        if (torch.is_grad_enabled()
+                and getattr(self, 'require_backward_grad_sync', False)
+                and self.require_backward_grad_sync):
             if self.find_unused_parameters:
                 self.reducer.prepare_for_backward(list(_find_tensors(output)))
             else:
@@ -86,8 +99,15 @@ class MMDistributedDataParallel(DistributedDataParallel):
                 'Reducer buckets have been rebuilt in this iteration.',
                 logger='mmcv')
 
-        if getattr(self, 'require_forward_param_sync', True):
-            self._sync_params()
+        if ('parrots' not in TORCH_VERSION
+                and digit_version(TORCH_VERSION) >= digit_version('1.11.0')):
+            if self._check_sync_bufs_pre_fwd():
+                self._sync_buffers()
+        else:
+            if (getattr(self, 'require_forward_param_sync', False)
+                    and self.require_forward_param_sync):
+                self._sync_params()
+
         if self.device_ids:
             inputs, kwargs = self.scatter(inputs, kwargs, self.device_ids)
             if len(self.device_ids) == 1:
@@ -99,8 +119,14 @@ class MMDistributedDataParallel(DistributedDataParallel):
         else:
             output = self.module.val_step(*inputs, **kwargs)
 
-        if torch.is_grad_enabled() and getattr(
-                self, 'require_backward_grad_sync', True):
+        if ('parrots' not in TORCH_VERSION
+                and digit_version(TORCH_VERSION) >= digit_version('1.11.0')):
+            if self._check_sync_bufs_post_fwd():
+                self._sync_buffers()
+
+        if (torch.is_grad_enabled()
+                and getattr(self, 'require_backward_grad_sync', False)
+                and self.require_backward_grad_sync):
             if self.find_unused_parameters:
                 self.reducer.prepare_for_backward(list(_find_tensors(output)))
             else: