I am using pytorch to train some x-ray images but I ran into the following issue:
in the line :  loss.backward() , the program just keeps running and never end, and there is no error or warning.
            loss, outputs = self.forward(images, targets)  
            loss = loss / self.accumulation_steps
            print("loss calculated: " + str(loss))

            if phase == "train":
                print("running loss backwarding!") 
                loss.backward()
                print("loss is backwarded!")
                if (itr + 1 ) % self.accumulation_steps == 0:
                    self.optimizer.step()
                    self.optimizer.zero_grad()

The loss calculated before this is something like  tensor(0.8598, grad_fn=<DivBackward0>) .
Could anyone help me with why this keeps running or any good ways to debug the backward() function?
I am using torch 1.2.0+cu92 with the compatible cuda 10.0.
Thank you so much!!