drm/i915: Fixing mutex deadlock window at eDP DRRS

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@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d1141d3..0a57763 100644 (file)
--- 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,