[Intel-gfx] [PATCH] drm/i915: Fixing mutex deadlock window at eDP DRRS

[Daniel Vetter]

On Wed, Mar 04, 2015 at 02:55:23PM -0800, Rodrigo Vivi wrote:
> Looks enough for me...
> 
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> 
> On Mon, Mar 2, 2015 at 10:41 PM, Ramalingam C <ramalingam.c at intel.com> wrote:
> > In invalidate and flush functions of eDP DRRS, if deferred downclock
> > work starts execution at a time window between acquiring the drrs
> > mutex and cancellation of the deferred work
> > (intel_edp_drrs_downclock_work), then deferred work will find
> > drrs mutex locked and wait for the same.
> >
> > Meanwhile the function that acquired mutex drrs invalidate/flush will
> > wait for the completion of the deferred work before releasing the mutex.
> > Thats a deadlock.
> >
> > To avoid such deadlock scenario, this change cancels the deferred work
> > before acquiring the mutex at invalidate and flush functions.
> >
> > Signed-off-by: Ramalingam C <ramalingam.c at intel.com>

Queued for -next, thanks for the patch.
-Daniel

> > ---
> >  drivers/gpu/drm/i915/intel_dp.c |    7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index d1141d3..0a57763 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4966,12 +4966,13 @@ void intel_edp_drrs_invalidate(struct drm_device *dev,
> >         if (!dev_priv->drrs.dp)
> >                 return;
> >
> > +       cancel_delayed_work_sync(&dev_priv->drrs.work);
> > +
> >         mutex_lock(&dev_priv->drrs.mutex);
> >         crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
> >         pipe = to_intel_crtc(crtc)->pipe;
> >
> >         if (dev_priv->drrs.refresh_rate_type == DRRS_LOW_RR) {
> > -               cancel_delayed_work_sync(&dev_priv->drrs.work);
> >                 intel_dp_set_drrs_state(dev_priv->dev,
> >                                 dev_priv->drrs.dp->attached_connector->panel.
> >                                 fixed_mode->vrefresh);
> > @@ -5004,13 +5005,13 @@ void intel_edp_drrs_flush(struct drm_device *dev,
> >         if (!dev_priv->drrs.dp)
> >                 return;
> >
> > +       cancel_delayed_work_sync(&dev_priv->drrs.work);
> > +
> >         mutex_lock(&dev_priv->drrs.mutex);
> >         crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
> >         pipe = to_intel_crtc(crtc)->pipe;
> >         dev_priv->drrs.busy_frontbuffer_bits &= ~frontbuffer_bits;
> >
> > -       cancel_delayed_work_sync(&dev_priv->drrs.work);
> > -
> >         if (dev_priv->drrs.refresh_rate_type != DRRS_LOW_RR &&
> >                         !dev_priv->drrs.busy_frontbuffer_bits)
> >                 schedule_delayed_work(&dev_priv->drrs.work,
> > --
> > 1.7.9.5
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> 
> 
> -- 
> Rodrigo Vivi
> Blog: http://blog.vivi.eng.br

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch