Re: [PATCH v3 2/3] drm/nouveau/kms/nv50-: Introduce nv50_wndw_default_state()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Unconditional dereference of `wndw->plane.state` which may be NULL if the initial state allocation fails.
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--- Patch [2]: [PATCH v3 2/3] drm/nouveau/kms/nv50-: Introduce nv50_wndw_default_state() ---
commit 2d2dcbda94d37e6b985a1775b04d636840fd94c1
Author: Lyude Paul <lyude@redhat.com>

drm/nouveau/kms/nv50-: Introduce nv50_wndw_default_state()

This commit introduces nv50_wndw_default_state() to ensure the initial
atomic state for a window always starts with a supported value in
pixel_blend_mode. It hooks this function into nv50_display_read_hw_state()
to enforce a valid blend mode value during driver startup.

> diff --git a/drivers/gpu/drm/nouveau/dispnv50/wndw.c b/drivers/gpu/drm/nouveau/dispnv50/wndw.c
> index 2635458d52acc..dfa1ba45acd99 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/wndw.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/wndw.c

[ ... ]

> +/*
> + * Setup defaults for the atomic wndw state
> + */
> +void
> +nv50_wndw_default_state(struct nv50_wndw *wndw)
> +{
> +	struct nv50_wndw_atom *armw = nv50_wndw_atom(wndw->plane.state);
> +	const unsigned int blend_modes = wndw->func->blend_modes;
> +
> +	drm_modeset_lock_assert_held(&wndw->plane.mutex);
> +
> +	/* Ensure the plane's atomic state didn't default to a pixel_blend_mode we don't support */
> +	if (blend_modes && (!(BIT(armw->state.pixel_blend_mode) & blend_modes))) {

[Severity: High]
Could this dereference a NULL pointer if memory allocation fails during
drm_mode_config_reset()?

If plane state allocation fails in the plane's reset hook, wndw->plane.state
is left as NULL. When nv50_display_read_hw_state() subsequently calls this
function, armw will evaluate to NULL, leading to a fault when accessing
armw->state.pixel_blend_mode.

> +		if (blend_modes & BIT(DRM_MODE_BLEND_COVERAGE))
> +			armw->state.pixel_blend_mode = DRM_MODE_BLEND_COVERAGE;
> +		else if (blend_modes & BIT(DRM_MODE_BLEND_PREMULTI))
> +			armw->state.pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> +		else if (blend_modes & BIT(DRM_MODE_BLEND_PIXEL_NONE))
> +			armw->state.pixel_blend_mode = DRM_MODE_BLEND_PIXEL_NONE;
> +	}
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260720215058.398210-1-lyude@redhat.com?part=2