Fix RWKV backward on GPU (huggingface#23774)

Author: sgugger

src/transformers/models/rwkv/modeling_rwkv.py

@@ -159,7 +159,7 @@ def forward(ctx, time_decay, time_first, key, value, state=None, return_state=Fa
 
     @staticmethod
     # g stands for grad
-    def backward(ctx, g_output):
+    def backward(ctx, g_output, g_state=None):
         input_dtype = ctx.input_dtype
 
         time_decay, time_first, key, value, output = ctx.saved_tensors
@@ -188,17 +188,14 @@ def backward(ctx, g_output):
             g_key,
             g_value,
         )
-        g_time_decay = torch.sum(g_time_decay, dim=0)
-        g_time_first = torch.sum(g_time_first, dim=0)
 
         return (
-            None,
-            None,
-            None,
             g_time_decay.to(input_dtype),
             g_time_first.to(input_dtype),
             g_key.to(input_dtype),
             g_value.to(input_dtype),
+            None,
+            None,
         )