[PATCH v2 02/12] drm/fb-helper: Avoid race with DRM userspace

[Maxime Ripard]

On Sun, Apr 07, 2019 at 06:52:33PM +0200, Noralf Trønnes wrote:
> drm_fb_helper_is_bound() is used to check if DRM userspace is in control.
> This is done by looking at the fb on the primary plane. By the time
> fb-helper gets around to committing, it's possible that the facts have
> changed.
>
> Avoid this race by holding the drm_device->master_mutex lock while
> committing. When DRM userspace does its first open, it will now wait
> until fb-helper is done. The helper will stay away if there's a master.
>
> Locking rule: Always take the fb-helper lock first.
>
> v2:
> - Remove drm_fb_helper_is_bound() (Daniel Vetter)
> - No need to check fb_helper->dev->master in
>   drm_fb_helper_single_fb_probe(), restore_fbdev_mode() has the check.
>
> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>

With the changes asked by Daniel,
Reviewed-by: Maxime Ripard <maxime.ripard at bootlin.com>

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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