Repository: pytorch
Issue: DISABLED test_streaming_backwards_callback (__main__.TestCuda)
Labels: module: cuda,triaged,module: flaky-tests,skipped

Platforms: linux

This test was disabled because it is failing in CI. See [recent examples](https://hud.pytorch.org/flakytest?name=test_streaming_backwards_callback&suite=TestCuda&limit=100) and the most recent trunk [workflow logs](https://github.com/pytorch/pytorch/runs/29601038632).

Over the past 3 hours, it has been determined flaky in 4 workflow(s) with 12 failures and 4 successes.

**Debugging instructions (after clicking on the recent samples link):**
DO NOT ASSUME THINGS ARE OKAY IF THE CI IS GREEN. We now shield flaky tests from developers so CI will thus be green but it will be harder to parse the logs.
To find relevant log snippets:
1. Click on the workflow logs linked above
2. Click on the Test step of the job so that it is expanded. Otherwise, the grepping will not work.
3. Grep for `test_streaming_backwards_callback`
4. There should be several instances run (as flaky tests are rerun in CI) from which you can study the logs.



<details><summary>Sample error message</summary>

```
Traceback (most recent call last):
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 1232, in not_close_error_metas
    pair.compare()
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 711, in compare
    self._compare_values(actual, expected)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 841, in _compare_values
    compare_fn(
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 1023, in _compare_regular_values_close
    if torch.all(matches):
RuntimeError: Host and device pointer dont match with cudaHostRegister. Please dont use this feature by setting PYTORCH_CUDA_ALLOC_CONF=use_cuda_host_register:False (default)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/jenkins/workspace/test/test_cuda.py", line 1343, in test_streaming_backwards_callback
    self.assertEqual(stash[0], torch.full_like(a, 6))
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_internal/common_utils.py", line 3846, in assertEqual
    error_metas = not_close_error_metas(
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 1239, in not_close_error_metas
    f"Comparing\n\n"
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 378, in __repr__
    body = [
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_comparison.py", line 379, in <listcomp>
    f"    {name}={value!s},"
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/_tensor.py", line 514, in __repr__
    return torch._tensor_str._str(self, tensor_contents=tensor_contents)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/_tensor_str.py", line 708, in _str
    return _str_intern(self, tensor_contents=tensor_contents)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/_tensor_str.py", line 625, in _str_intern
    tensor_str = _tensor_str(self, indent)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/_tensor_str.py", line 357, in _tensor_str
    formatter = _Formatter(get_summarized_data(self) if summarize else self)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/_tensor_str.py", line 145, in __init__
    nonzero_finite_vals = torch.masked_select(
RuntimeError: Host and device pointer dont match with cudaHostRegister. Please dont use this feature by setting PYTORCH_CUDA_ALLOC_CONF=use_cuda_host_register:False (default)

To execute this test, run the following from the base repo dir:
    python test/test_cuda.py TestCuda.test_streaming_backwards_callback

This message can be suppressed by setting PYTORCH_PRINT_REPRO_ON_FAILURE=0
```

</details>


Test file path: `test_cuda_expandable_segments.py`

cc @ptrblck @msaroufim @clee2000