[RTDETR]fix "Grad strides do not match bucket view strides" when training with DDP (#3255)

ultralytics/nn/modules/transformer.py

@@ -77,7 +77,7 @@ class AIFI(TransformerEncoderLayer):
         pos_embed = self.build_2d_sincos_position_embedding(w, h, c)
         # flatten [B, C, H, W] to [B, HxW, C]
         x = super().forward(x.flatten(2).permute(0, 2, 1), pos=pos_embed.to(device=x.device, dtype=x.dtype))
-        return x.permute((0, 2, 1)).view([-1, c, h, w])
+        return x.permute(0, 2, 1).view([-1, c, h, w]).contiguous()
 
     @staticmethod
     def build_2d_sincos_position_embedding(w, h, embed_dim=256, temperature=10000.):

ultralytics/vit/utils/ops.py

@@ -31,9 +31,6 @@ class HungarianMatcher(nn.Module):
         _cost_mask(bs, num_gts, masks=None, gt_mask=None): Computes the mask cost and dice cost if masks are predicted.
     """
 
-    class HungarianMatcher(nn.Module):
-        ...
-
     def __init__(self, cost_gain=None, use_fl=True, with_mask=False, num_sample_points=12544, alpha=0.25, gamma=2.0):
         super().__init__()
         if cost_gain is None: