On Thu, Sep 05, 2019 at 12:41:27PM +0200, Daniel Vetter wrote:
> 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.
drm_modeset_lock eats EALREADY and returns 0 for that case, so I guess it
depends _how_ paranoid you want to be here :-)
>
> 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.
Ok, had a chance to run through some tests this morning with
CONFIG_DEBUG_WW_MUTEX_SLOWPATH and things lgtm
Sean
> -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
--
Sean Paul, Software Engineer, Google / Chromium OS
