drm/i915: Free pending page flip events at .preclose()

If there are pending page flips when the fd gets closed those page
flips may have events associated to them. When the page flip eventually
completes it will queue the event to file_priv->event_list, but that
may be too late and file_priv->event_list has already been cleaned up.
Thus we leak a bit of kernel memory in the form of the event structure.

To avoid such problems clear out such pending events from
intel_crtc->unpin_work at ->preclose(). Any event that already made it
to file_priv->event_list will get cleaned up by the drm_release_events()
a bit later.

We can ignore the file_priv->event_space accounting since file_priv is
going away. This is already how drm core deals with pending vblank
events, which are maintained by the drm core.

What saves us from a total disaster (ie. dereferencing and alrady
freed file_priv) is the fact that the fb descruction triggers a modeset
and there we wait for pending flips.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1981,6 +1981,9 @@ void i915_driver_preclose(struct drm_device *dev, struct drm_file *file)
 	i915_gem_context_close(dev, file);
 	i915_gem_release(dev, file);
 	mutex_unlock(&dev->struct_mutex);
+
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		intel_modeset_preclose(dev, file);
 }
 
 void i915_driver_postclose(struct drm_device *dev, struct drm_file *file)

drivers/gpu/drm/i915/intel_display.c

@@ -13470,3 +13470,25 @@ intel_display_print_error_state(struct drm_i915_error_state_buf *m,
 		err_printf(m, "  VSYNC: %08x\n", error->transcoder[i].vsync);
 	}
 }
+
+void intel_modeset_preclose(struct drm_device *dev, struct drm_file *file)
+{
+	struct intel_crtc *crtc;
+
+	for_each_intel_crtc(dev, crtc) {
+		struct intel_unpin_work *work;
+		unsigned long irqflags;
+
+		spin_lock_irqsave(&dev->event_lock, irqflags);
+
+		work = crtc->unpin_work;
+
+		if (work && work->event &&
+		    work->event->base.file_priv == file) {
+			kfree(work->event);
+			work->event = NULL;
+		}
+
+		spin_unlock_irqrestore(&dev->event_lock, irqflags);
+	}
+}

drivers/gpu/drm/i915/intel_drv.h

@@ -892,6 +892,7 @@ void intel_mode_from_pipe_config(struct drm_display_mode *mode,
 				 struct intel_crtc_config *pipe_config);
 int intel_format_to_fourcc(int format);
 void intel_crtc_wait_for_pending_flips(struct drm_crtc *crtc);
+void intel_modeset_preclose(struct drm_device *dev, struct drm_file *file);
 
 /* intel_dp.c */
 void intel_dp_init(struct drm_device *dev, int output_reg, enum port port);