When I run my code, this message is displayed: How can I fix it? I’m writing a neural network with pytorch-lightning and dgl with multiple optimizers, and I’m training with ddp on 1 gpu.
Traceback (most recent call last):
  File "main.py", line 50, in <module>
    trainer.fit(model, train_loader, val_loader)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/trainer.py", line 439, in fit
    results = self.accelerator_backend.train()
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/accelerators/ddp_accelerator.py", line 146, in train
    results = self.ddp_train(process_idx=self.task_idx, model=model)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/accelerators/ddp_accelerator.py", line 279, in ddp_train
    results = self.train_or_test()
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/accelerators/accelerator.py", line 66, in train_or_test
    results = self.trainer.train()
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/trainer.py", line 482, in train
    self.train_loop.run_training_epoch()
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 541, in run_training_epoch
    batch_output = self.run_training_batch(batch, batch_idx, dataloader_idx)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 678, in run_training_batch
    self.trainer.hiddens
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 760, in training_step_and_backward
    result = self.training_step(split_batch, batch_idx, opt_idx, hiddens)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 304, in training_step
    training_step_output = self.trainer.accelerator_backend.training_step(args)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/accelerators/ddp_accelerator.py", line 156, in training_step
    output = self.trainer.model(*args)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/nn/modules/module.py", line 550, in __call__
    result = self.forward(*input, **kwargs)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/overrides/data_parallel.py", line 176, in forward
    output = self.module.training_step(*inputs[0], **kwargs[0])
  File "/afs/ece.cmu.edu/usr/xujinl/dynamic_grpah_pooling_rl/gcn_w_dyn_pool.py", line 195, in training_step
    self.manual_backward(L_est, opts[1], retain_graph=True)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/core/lightning.py", line 1081, in manual_backward
    self.trainer.train_loop.backward(loss, optimizer, -1, *args, **kwargs)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 781, in backward
    self.trainer.accelerator_backend.backward(result, optimizer, opt_idx, *args, **kwargs)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/pytorch_lightning/accelerators/accelerator.py", line 98, in backward
    closure_loss.backward(*args, **kwargs)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/tensor.py", line 198, in backward
    torch.autograd.backward(self, gradient, retain_graph, create_graph)
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/autograd/__init__.py", line 100, in backward
    allow_unreachable=True)  # allow_unreachable flag
RuntimeError: has_marked_unused_parameters_ INTERNAL ASSERT FAILED at /opt/conda/conda-bld/pytorch_1591914880026/work/torch/csrc/distributed/c10d/reducer.cpp:327, please report a bug to PyTorch.  (mark_variable_ready at /opt/conda/conda-bld/pytorch_1591914880026/work/torch/csrc/distributed/c10d/reducer.cpp:327)
frame #0: c10::Error::Error(c10::SourceLocation, std::string const&) + 0x4e (0x7f27ea039b5e in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libc10.so)
frame #1: c10d::Reducer::mark_variable_ready(c10d::Reducer::VariableIndex) + 0x9ba (0x7f2817a1b3aa in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_python.so)
frame #2: c10d::Reducer::autograd_hook(c10d::Reducer::VariableIndex) + 0x2d0 (0x7f2817a1b910 in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_python.so)
frame #3: <unknown function> + 0x8a395c (0x7f2817a1095c in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_python.so)
frame #4: torch::autograd::Engine::evaluate_function(std::shared_ptr<torch::autograd::GraphTask>&, torch::autograd::Node*, torch::autograd::InputBuffer&) + 0x60d (0x7f281412d00d in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_cpu.so)
frame #5: torch::autograd::Engine::thread_main(std::shared_ptr<torch::autograd::GraphTask> const&, bool) + 0x3d2 (0x7f281412eed2 in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_cpu.so)
frame #6: torch::autograd::Engine::thread_init(int) + 0x39 (0x7f2814127549 in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_cpu.so)
frame #7: torch::autograd::python::PythonEngine::thread_init(int) + 0x38 (0x7f2817677638 in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/libtorch_python.so)
frame #8: <unknown function> + 0xc819d (0x7f2819ed219d in /afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/torch/lib/../../../.././libstdc++.so.6)
frame #9: <unknown function> + 0x7ea5 (0x7f2838eebea5 in /lib64/libpthread.so.0)
frame #10: clone + 0x6d (0x7f2838c148cd in /lib64/libc.so.6)

Exception ignored in: <function tqdm.__del__ at 0x7f27dcf30b90>
Traceback (most recent call last):
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/tqdm/std.py", line 1122, in __del__
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/tqdm/std.py", line 1335, in close
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/tqdm/std.py", line 1514, in display
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/tqdm/std.py", line 1125, in __repr__
  File "/afs/ece.cmu.edu/usr/xujinl/anaconda3/envs/CSD/lib/python3.7/site-packages/tqdm/std.py", line 1475, in format_dict
TypeError: cannot unpack non-iterable NoneType object