[PATCH] drm/i915: Protect fbdev across slow or failed initialisation

[Chris Wilson <chris@chris-wilson.co.uk>]

If the initialisation fails, we may be left with a dangling pointer with
an incomplete fbdev structure. Here we want to disable internal calls
into fbdev. Similarly, the initialisation may be slow and we haven't yet
enabled the fbdev (e.g. quick suspend or last-close before the async init
completes).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93580
Reported-by: "Li, Weinan Z" <weinan.z.li@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 48 ++++++++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 51a5e39e52f2..0bae91268a12 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -114,6 +114,24 @@ static struct fb_ops intelfb_ops = {
 	.fb_debug_leave = drm_fb_helper_debug_leave,
 };
 
+static struct intel_fbdev *intel_fbdev_get_if_active(struct drm_device *dev)
+{
+	struct drm_i915_device *dev_priv = to_i915(dev);
+	struct fb_info *info;
+
+	if (dev_priv->fbdev == NULL)
+		return NULL;
+
+	info = ifbdev->helper.fbdev;
+	if (info->screen_base == NULL)
+		return NULL;
+
+	if (info->state != FBINFO_STATE_RUNNING)
+		return NULL;
+
+	return dev_priv->fbdev;
+}
+
 static int intelfb_alloc(struct drm_fb_helper *helper,
 			 struct drm_fb_helper_surface_size *sizes)
 {
@@ -764,6 +782,8 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
 		return;
 
 	info = ifbdev->helper.fbdev;
+	if (info->screen_base == NULL)
+		return;
 
 	if (synchronous) {
 		/* Flush any pending work to turn the console on, and then
@@ -805,32 +825,24 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
 
 void intel_fbdev_output_poll_changed(struct drm_device *dev)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_fbdev *ifbdev = intel_fbdev_get_if_active(dev);
+
+	if (ifbdev == NULL)
+		return;
 
-	async_synchronize_full();
-	if (dev_priv->fbdev)
-		drm_fb_helper_hotplug_event(&dev_priv->fbdev->helper);
+	drm_fb_helper_hotplug_event(&ifbdev->helper);
 }
 
 void intel_fbdev_restore_mode(struct drm_device *dev)
 {
-	int ret;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_fbdev *ifbdev = dev_priv->fbdev;
-	struct drm_fb_helper *fb_helper;
+	struct intel_fbdev *ifbdev = intel_fbdev_get_if_active(dev);
 
-	async_synchronize_full();
-	if (!ifbdev)
+	if (ifbdev == NULL)
 		return;
 
-	fb_helper = &ifbdev->helper;
-
-	ret = drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper);
-	if (ret) {
-		DRM_DEBUG("failed to restore crtc mode\n");
-	} else {
-		mutex_lock(&fb_helper->dev->struct_mutex);
+	if (drm_fb_helper_restore_fbdev_mode_unlocked(&ifbdev->helper) == 0) {
+		mutex_lock(&dev->struct_mutex);
 		intel_fb_obj_invalidate(ifbdev->fb->obj, ORIGIN_GTT);
-		mutex_unlock(&fb_helper->dev->struct_mutex);
+		mutex_unlock(&dev->struct_mutex);
 	}
 }
-- 
2.8.0.rc3

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