On Wed, Sep 4, 2019 at 10:29 PM Sean Paul <sean@xxxxxxxxxx> wrote:
>
> From: Sean Paul <seanpaul@xxxxxxxxxxxx>
>
> Since the dirtyfb ioctl doesn't give us any hints as to which plane is
> scanning out the fb it's marking as damaged, we need to loop through
> planes to find it.
>
> Currently we just reach into plane state and check, but that can race
> with another commit changing the fb out from under us. This patch locks
> the plane before checking the fb and will release the lock if the plane
> is not displaying the dirty fb.
>
> Fixes: b9fc5e01d1ce ("drm: Add helper to implement legacy dirtyfb")
> Cc: Rob Clark <robdclark@xxxxxxxxx>
> Cc: Deepak Rawat <drawat@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
> Cc: Sean Paul <sean@xxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.0+
> Reported-by: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_damage_helper.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
> index 8230dac01a89..3a4126dc2520 100644
> --- a/drivers/gpu/drm/drm_damage_helper.c
> +++ b/drivers/gpu/drm/drm_damage_helper.c
> @@ -212,8 +212,14 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
> drm_for_each_plane(plane, fb->dev) {
> struct drm_plane_state *plane_state;
>
> - if (plane->state->fb != fb)
> + ret = drm_modeset_lock(&plane->mutex, state->acquire_ctx);
> + if (ret)
I think for paranoid safety we should have a WARN_ON(ret == -EALREADY)
here. It should be impossible, but if it's not for some oddball
reason, we'll blow up.
With that: Reviewed-by: Daniel Vetter <daniel@xxxxxxxx>
But please give this a spin with some workloads and the ww_mutex
slowpath debugging enabled, just to makre sure.
-Daniel
> + goto out;
> +
> + if (plane->state->fb != fb) {
> + drm_modeset_unlock(&plane->mutex);
> continue;
> + }
>
> plane_state = drm_atomic_get_plane_state(state, plane);
> if (IS_ERR(plane_state)) {
> --
> Sean Paul, Software Engineer, Google / Chromium OS
>
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
