Fix Idefics vision embedding mismatched devices
Author: sayandipdutta
Pull request: yes
Labels: name: duplicate

# What does this PR do?

In the following section: https://github.com/huggingface/transformers/blob/a1a4fcd03e3455772415e6400fee91f3159e7ac5/src/transformers/models/idefics3/modeling_idefics3.py#L143-L160

`boundaries` and `position_ids` are getting created on `cpu`, and the `input` device information is not passed through. However, `patch_attention_mask` (input to the `forward` method) carries the `device` chosen at the call-site. While using device other than `cpu`, in the `for` loop, `p_attn_mask` and consequently `nb_patches_{h/w}` are on the input device. Making the `device` to `position_ids.device` on line `150-151` doesn't solve the issue, since they are already on `cpu`. 
_**This PR moves `boundaries` and `position_ids` to `patch_attention_mask.device`.**_

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Fixes #40116 


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Comments:
**[For maintainers]** Suggested jobs to run (before merge)

run-slow: idefics2, idefics3

Thanks, this is already addressed in https://github.com/huggingface/transformers/pull/39975

@qgallouedec thanks! I will close it. For posterity, can you tell me what's the process of changing modeling_smolvlm.py? It is written in the file not to edit it manually.

@sayandipdutta you modify the underlying `modular_smolvlm.py` file, and run `make fix-copies` to propagate changes to modeling files

Addressed in #39975