Windows: RuntimeError: cuda runtime error (801) & RuntimeError: Expected object of scalar type Long but got scalar type

I am using fastai v2 on a windows system and testing on the pets notebook.

Current version:

Cuda: True
GPU: GeForce GTX 1060
Python version: 3.7.4 (default, Aug 9 2019, 18:34:13) [MSC v.1915 64 bit (AMD64)]
Pytorch version: 1.3.0

I got the following error after running this code:

pets = DataBlock(types=(PILImage, Category),
#get_y=RegexLabeller(pat = r’/([^/]+)\d+.jpg$’))
get_y = RegexLabeller(pat = r’\([^\]+)
\d+.jpg$’)) #For windows

dbunch = pets.databunch(untar_data(URLs.PETS)/“images”, item_tfms=RandomResizedCrop(460, min_scale=0.75), bs=32,
batch_tfms=[*aug_transforms(size=224, max_warp=0), Normalize(*imagenet_stats)])


results in the following error:

RuntimeError: cuda runtime error (801) : operation not supported at C:\w\1\s\tmp_conda_3.7_183424\conda\conda-bld\pytorch_1570818936694\work\torch/csrc/generic/StorageSharing.cpp:245

Looking at this thread it points that multiprocessing on CUDA tensors are not supported and offered 2 alternatives one being change num_worker to 0, which I did:

dbunch = pets.databunch(untar_data(URLs.PETS)/“images”, item_tfms=RandomResizedCrop(460, min_scale=0.75), bs=32,
batch_tfms=[*aug_transforms(size=224, max_warp=0), Normalize(*imagenet_stats)], num_workers=0)

This then resulted in a different error when running one_fit:

RuntimeError: Expected object of scalar type Long but got scalar type Int for argument #2 ‘target’ in call to _thnn_nll_loss_forward

The error was being generated here:

~\Anaconda3\envs\fastai_v2_1.3\lib\site-packages\torch\nn\ in nll_loss(input, target, weight, size_average, ignore_index, reduce, reduction)
1837 if dim == 2:
-> 1838 ret = torch._C._nn.nll_loss(input, target, weight, _Reduction.get_enum(reduction), ignore_index)
1839 elif dim == 4:
1840 ret = torch._C._nn.nll_loss2d(input, target, weight, _Reduction.get_enum(reduction), ignore_index)

so I added a line:

if dim == 2:
    target = target.long() #new input
    ret = torch._C._nn.nll_loss(input, target, weight, _Reduction.get_enum(reduction), ignore_index)

and now the notebook works fine.

However are there better suggestions on how to fix this?

1 Like

This is because we removed the automatic conversions to long ints in the data preprocesseing pipeline, since we wondered why it was there (now we know :slight_smile: ). There’ll be a fix today.


Awesome thanks!

@amritv Does the latest version work for you now? I am getting a similar error on windows after completion of the first epoch in the pets notebook

RuntimeError: Expected object of scalar type Int but got scalar type Long for argument #2 ‘other’

coming from

fastai_dev\fastai2\ in _f(self, *args, **kwargs)
155 def _f(self, *args, **kwargs):
156 cls = self.class
–> 157 res = getattr(super(TensorBase, self), fn)(*args, **kwargs)
158 return cls(res) if isinstance(res,Tensor) else res
159 return _f

Hey @cudawarped, just tried it out and it worked after a

git pull


conda env update

However I notice that your error was generated elsewhere.

1 Like

Hey @amritv thanks a million for checking

conda env update

has removed the errors and its training without issue.

1 Like

@sgugger, the issue still exists in the recent release for windows… I use 1.2 torch since 1.3 is not available on their site with cuda… the peds example not working…

d:\conda3\lib\site-packages\fastai2\ in accumulate(self, learn)
431 def accumulate(self, learn):
432 bs = find_bs(learn.yb)
–> 433 += to_detach(self.func(learn.pred, *learn.yb))*bs
434 self.count += bs
435 @property

d:\conda3\lib\site-packages\fastai2\ in error_rate(inp, targ, axis)
79 def error_rate(inp, targ, axis=-1):
80 "1 - accuracy"
—> 81 return 1 - accuracy(inp, targ, axis=axis)
83 # Cell

d:\conda3\lib\site-packages\fastai2\ in accuracy(inp, targ, axis)
74 “Compute accuracy with targ when pred is bs * n_classes”
75 pred,targ = flatten_check(inp.argmax(dim=axis), targ)
—> 76 return (pred == targ).float().mean()
78 # Cell

d:\conda3\lib\site-packages\fastai2\ in _f(self, *args, **kwargs)
270 def _f(self, *args, **kwargs):
271 cls = self.class
–> 272 res = getattr(super(TensorBase, self), fn)(*args, **kwargs)
273 return retain_type(res, self)
274 return _f

RuntimeError: Expected object of scalar type Int but got scalar type Long for argument #2 ‘other’

fastai v2 has not been tested on Windows and support for windows is not a priority right now (first, let’s finish it and document it :wink: ). I don’t think this will be dealt with until March.


Linking another answer to this thread which allowed me to fix this specific cuda runtime 801 error in intro notebook of fastbook.
Setting num_workers=0 in ImageDataLoaders.from_name_func made it work for me.


Hey, besides adding num_workers=0 to run in Windows, I created an auxiliary loss function in my notebook (instead of modifying the fastai library code):

def loss_aux(input, target, **kwargs):
  target = target.long()
  return F.cross_entropy(input, target, **kwargs)

And set it up in the learner:

learn = Learner(dls, simple_cnn, loss_func=loss_aux, metrics=accuracy)

I didn’t come up with this by myself, other posts suggested doing this for the metrics argument. Also tried updating to latest pytorch and fastai (2.0.9) before doing this.

Hope this helps someone.


Yeah, set num_workers=0

path = untar_data(URLs.PETS)/'images'

def is_cat(x): return x[0].isupper()
dls = ImageDataLoaders.from_name_func(
    path, get_image_files(path), valid_pct=0.2, seed=42,
    label_func=is_cat, item_tfms=Resize(224), 

learn = cnn_learner(dls, resnet34, metrics=error_rate)

Apparently Window’s 10 CUDA doesn’t support this feature (GPU memory sharing?).
See here: Windows FAQ — PyTorch 1.7.0 documentation

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