Re: [PATCH v6] usb: gadget: uvc: Fix deadlocks in uvcg_configfs attribute callbacks

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] usb: gadget: uvc: missing Fixes trailer for su_mutex deadlock
  fix
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commit aca7deea58b6e580c30b8b5a2d20ca884047e359
Author: Saad Varshani <varshanisaad@gmail.com>

> usb: gadget: uvc: Fix deadlocks in uvcg_configfs attribute callbacks
>
> Removed su_mutex locking in the function uvcg_extension_bm_controls_store.
> Done this due to the deadlock caused by the mutex conflict in
> fs/configfs_write_iter. Validated commit with the C repro provided by
> syzbot. No other conficts observed.
>
> Also removed the su_mutex in the other attribute extension functions.
> Such as uvcg_extension_b_control_size_store. This applies to all
> uvcg_configfs attribute store/show functions.
>
> The deadlock was happening due to a circular mutex dependency between
> configfs (frag_sem) and uvcg_extension su_mutex. The reason it is safe
> to traverse item->ci_parent without su_mutex is because
> configfs_write_iter() calls flush_write_buffer() which calls the
> attribute function, holding frag_sem. Which prevents configfs_rmdir()
> from unlinking the item or its ci_parent hierarchy
>
> Also reordered fmt->linked in uvcg_frame_b_frame_index_show() to be
> under the &opts->lock. As well as reorder refcnt in uvcg_color_matching
> store to be under &opts->lock.
>
> Applied opts->lock mutex, to functions uvcg_format_allow_link(),
> uvcg_format_drop_link(), uvcg_uncompressed_make(), uvcg_mjpeg_make(),
> and uvcg_framebased_make() due to them also modifying
> color_match->refcnt, to avoid concurrency issues.

[Severity: Low]
Since this fixes the su_mutex deadlock in the UVC configfs attribute
callbacks, should it include a Fixes: tag for the commit that introduced
that locking?

  Fixes: 46919a23ee87 ("usb: gadget: uvc: configfs support in uvc function")

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Sashiko AI review · https://sashiko.dev/#/patchset/20261107051544.4381-1-varshanisaad@gmail.com?part=1