[PATCH v4 1/2] 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).

v3: To create a typo introduced when retyping
v4: Prevent info==NULL dereference in early boot

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93580
Reported-by: "Li, Weinan Z" <weinan.z.li@intel.com>
Tested-by: Gabriel Feceoru <gabriel.feceoru@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 72 +++++++++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 153ea7a3fcf6..5d4be71bdf22 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -756,17 +756,47 @@ void intel_fbdev_fini(struct drm_device *dev)
 	dev_priv->fbdev = NULL;
 }
 
+static struct intel_fbdev *intel_fbdev_get(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct fb_info *info;
+
+	if (dev_priv->fbdev == NULL)
+		return NULL;
+
+	info = dev_priv->fbdev->helper.fbdev;
+	if (info == NULL)
+		return NULL;
+
+	if (info->screen_base == NULL)
+		return NULL;
+
+	return dev_priv->fbdev;
+}
+
+static struct intel_fbdev *intel_fbdev_get_if_active(struct drm_device *dev)
+{
+	struct intel_fbdev *ifbdev;
+
+	ifbdev = intel_fbdev_get(dev);
+	if (ifbdev == NULL)
+		return NULL;
+
+	if (ifbdev->helper.fbdev->state != FBINFO_STATE_RUNNING)
+		return NULL;
+
+	return ifbdev;
+}
+
 void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_fbdev *ifbdev = dev_priv->fbdev;
-	struct fb_info *info;
+	struct intel_fbdev *ifbdev;
 
-	if (!ifbdev)
+	ifbdev = intel_fbdev_get(dev);
+	if (ifbdev == NULL)
 		return;
 
-	info = ifbdev->helper.fbdev;
-
 	if (synchronous) {
 		/* Flush any pending work to turn the console on, and then
 		 * wait to turn it off. It must be synchronous as we are
@@ -798,8 +828,10 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
 	 * been restored from swap. If the object is stolen however, it will be
 	 * full of whatever garbage was left in there.
 	 */
-	if (state == FBINFO_STATE_RUNNING && ifbdev->fb->obj->stolen)
+	if (state == FBINFO_STATE_RUNNING && ifbdev->fb->obj->stolen) {
+		struct fb_info *info = ifbdev->helper.fbdev;
 		memset_io(info->screen_base, 0, info->screen_size);
+	}
 
 	drm_fb_helper_set_suspend(&ifbdev->helper, state);
 	console_unlock();
@@ -807,32 +839,24 @@ 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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