[Fix] Fix the bug that mit cannot process init_cfg (#1102)

* [Fix] Fix the bug that mit cannot process init_cfg

* fix error

mmseg/models/backbones/mit.py

@@ -9,9 +9,8 @@ from mmcv.cnn.bricks.drop import build_dropout
 from mmcv.cnn.bricks.transformer import MultiheadAttention
 from mmcv.cnn.utils.weight_init import (constant_init, normal_init,
                                         trunc_normal_init)
-from mmcv.runner import BaseModule, ModuleList, Sequential, _load_checkpoint
+from mmcv.runner import BaseModule, ModuleList, Sequential
 
-from ...utils import get_root_logger
 from ..builder import BACKBONES
 from ..utils import PatchEmbed, nchw_to_nlc, nlc_to_nchw
 
@@ -341,16 +340,18 @@ class MixVisionTransformer(BaseModule):
                  norm_cfg=dict(type='LN', eps=1e-6),
                  pretrained=None,
                  init_cfg=None):
-        super().__init__(init_cfg=init_cfg)
+        super(MixVisionTransformer, self).__init__(init_cfg=init_cfg)
 
-        if isinstance(pretrained, str) or pretrained is None:
-            warnings.warn('DeprecationWarning: pretrained is a deprecated, '
+        assert not (init_cfg and pretrained), \
+            'init_cfg and pretrained cannot be set at the same time'
+        if isinstance(pretrained, str):
+            warnings.warn('DeprecationWarning: pretrained is deprecated, '
                           'please use "init_cfg" instead')
-        else:
+            self.init_cfg = dict(type='Pretrained', checkpoint=pretrained)
+        elif pretrained is not None:
             raise TypeError('pretrained must be a str or None')
 
         self.embed_dims = embed_dims
-
         self.num_stages = num_stages
         self.num_layers = num_layers
         self.num_heads = num_heads
@@ -362,7 +363,6 @@ class MixVisionTransformer(BaseModule):
 
         self.out_indices = out_indices
         assert max(out_indices) < self.num_stages
-        self.pretrained = pretrained
 
         # transformer encoder
         dpr = [
@@ -401,7 +401,7 @@ class MixVisionTransformer(BaseModule):
             cur += num_layer
 
     def init_weights(self):
-        if self.pretrained is None:
+        if self.init_cfg is None:
             for m in self.modules():
                 if isinstance(m, nn.Linear):
                     trunc_normal_init(m, std=.02, bias=0.)
@@ -413,16 +413,8 @@ class MixVisionTransformer(BaseModule):
                     fan_out //= m.groups
                     normal_init(
                         m, mean=0, std=math.sqrt(2.0 / fan_out), bias=0)
-        elif isinstance(self.pretrained, str):
-            logger = get_root_logger()
-            checkpoint = _load_checkpoint(
-                self.pretrained, logger=logger, map_location='cpu')
-            if 'state_dict' in checkpoint:
-                state_dict = checkpoint['state_dict']
-            else:
-                state_dict = checkpoint
-
-            self.load_state_dict(state_dict, False)
+        else:
+            super(MixVisionTransformer, self).init_weights()
 
     def forward(self, x):
         outs = []

tests/test_models/test_backbones/test_mit.py

@@ -55,3 +55,59 @@ def test_mit():
     # Out identity
     outs = MHA(temp, hw_shape, temp)
     assert out.shape == (1, token_len, 64)
+
+
+def test_mit_init():
+    path = 'PATH_THAT_DO_NOT_EXIST'
+    # Test all combinations of pretrained and init_cfg
+    # pretrained=None, init_cfg=None
+    model = MixVisionTransformer(pretrained=None, init_cfg=None)
+    assert model.init_cfg is None
+    model.init_weights()
+
+    # pretrained=None
+    # init_cfg loads pretrain from an non-existent file
+    model = MixVisionTransformer(
+        pretrained=None, init_cfg=dict(type='Pretrained', checkpoint=path))
+    assert model.init_cfg == dict(type='Pretrained', checkpoint=path)
+    # Test loading a checkpoint from an non-existent file
+    with pytest.raises(OSError):
+        model.init_weights()
+
+    # pretrained=None
+    # init_cfg=123, whose type is unsupported
+    model = MixVisionTransformer(pretrained=None, init_cfg=123)
+    with pytest.raises(TypeError):
+        model.init_weights()
+
+    # pretrained loads pretrain from an non-existent file
+    # init_cfg=None
+    model = MixVisionTransformer(pretrained=path, init_cfg=None)
+    assert model.init_cfg == dict(type='Pretrained', checkpoint=path)
+    # Test loading a checkpoint from an non-existent file
+    with pytest.raises(OSError):
+        model.init_weights()
+
+    # pretrained loads pretrain from an non-existent file
+    # init_cfg loads pretrain from an non-existent file
+    with pytest.raises(AssertionError):
+        MixVisionTransformer(
+            pretrained=path, init_cfg=dict(type='Pretrained', checkpoint=path))
+    with pytest.raises(AssertionError):
+        MixVisionTransformer(pretrained=path, init_cfg=123)
+
+    # pretrain=123, whose type is unsupported
+    # init_cfg=None
+    with pytest.raises(TypeError):
+        MixVisionTransformer(pretrained=123, init_cfg=None)
+
+    # pretrain=123, whose type is unsupported
+    # init_cfg loads pretrain from an non-existent file
+    with pytest.raises(AssertionError):
+        MixVisionTransformer(
+            pretrained=123, init_cfg=dict(type='Pretrained', checkpoint=path))
+
+    # pretrain=123, whose type is unsupported
+    # init_cfg=123, whose type is unsupported
+    with pytest.raises(AssertionError):
+        MixVisionTransformer(pretrained=123, init_cfg=123)