[QAT] Fix the runtime run `cannot resize variables that require grad` (#57068)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57068
When training with histogram observer on, we got this runtime error:
```
torch/quantization/observer.py", line 942, in forward
self.bins)
self.histogram.resize_(combined_histogram.shape)
~~~~~~~~~~~~~~~~~~~~~~ <--- HERE
self.histogram.copy_(combined_histogram)
self.min_val.resize_(combined_min.shape)
RuntimeError: cannot resize variables that require grad
```
Since this is the histogram observer that is used to collect histogram information, should not need gradient. So turn off the grad before resizing using `detach_()` method.
Test Plan:
- arc lint
- Train with histogram observer turned on, training finished successfully
f264139727
Reviewed By: supriyar
Differential Revision: D27147212
fbshipit-source-id: abed5b9c4570ffc6bb60e58e64791cfce66856cd
