drm/i915: Fix locking in DRRS flush/invalidate hooks

We must acquire the mutex before we can check drrs.dp, otherwise
someone might sneak in with a modeset, clear the pointer after we've
checked it and then the code will Oops.

This issue has been introduced in

commit a93fad0f7fb8a3ff12e8814b630648f6d187954c
Author: Vandana Kannan <vandana.kannan@intel.com>
Date:   Sat Jan 10 02:25:59 2015 +0530

    drm/i915: DRRS calls based on frontbuffer

v2: Don't blow up on uninitialized mutex and work item by checking
whether DRRS is support or not first. Also unconditionally initialize
the mutex/work item to avoid future trouble.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Vandana Kannan <vandana.kannan@intel.com>
Cc: stable@vger.kernel.org (4.0+ only)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index b70e635..5e60473 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -5157,7 +5157,6 @@ static void intel_edp_drrs_downclock_work(struct work_struct *work)
                        downclock_mode->vrefresh);
 
 unlock:
-
        mutex_unlock(&dev_priv->drrs.mutex);
 }
 
@@ -5179,12 +5178,17 @@ void intel_edp_drrs_invalidate(struct drm_device *dev,
        struct drm_crtc *crtc;
        enum pipe pipe;
 
-       if (!dev_priv->drrs.dp)
+       if (dev_priv->drrs.type == DRRS_NOT_SUPPORTED)
                return;
 
        cancel_delayed_work_sync(&dev_priv->drrs.work);
 
        mutex_lock(&dev_priv->drrs.mutex);
+       if (!dev_priv->drrs.dp) {
+               mutex_unlock(&dev_priv->drrs.mutex);
+               return;
+       }
+
        crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
        pipe = to_intel_crtc(crtc)->pipe;
 
@@ -5218,12 +5222,17 @@ void intel_edp_drrs_flush(struct drm_device *dev,
        struct drm_crtc *crtc;
        enum pipe pipe;
 
-       if (!dev_priv->drrs.dp)
+       if (dev_priv->drrs.type == DRRS_NOT_SUPPORTED)
                return;
 
        cancel_delayed_work_sync(&dev_priv->drrs.work);
 
        mutex_lock(&dev_priv->drrs.mutex);
+       if (!dev_priv->drrs.dp) {
+               mutex_unlock(&dev_priv->drrs.mutex);
+               return;
+       }
+
        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;
@@ -5294,6 +5303,9 @@ intel_dp_drrs_init(struct intel_connector *intel_connector,
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct drm_display_mode *downclock_mode = NULL;
 
+       INIT_DELAYED_WORK(&dev_priv->drrs.work, intel_edp_drrs_downclock_work);
+       mutex_init(&dev_priv->drrs.mutex);
+
        if (INTEL_INFO(dev)->gen <= 6) {
                DRM_DEBUG_KMS("DRRS supported for Gen7 and above\n");
                return NULL;
@@ -5312,10 +5324,6 @@ intel_dp_drrs_init(struct intel_connector *intel_connector,
                return NULL;
        }
 
-       INIT_DELAYED_WORK(&dev_priv->drrs.work, intel_edp_drrs_downclock_work);
-
-       mutex_init(&dev_priv->drrs.mutex);
-
        dev_priv->drrs.type = dev_priv->vbt.drrs_type;
 
        dev_priv->drrs.refresh_rate_type = DRRS_HIGH_RR;