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

[Lukas Wunner <lukas@wunner.de>]

Hi,

On Wed, Feb 03, 2016 at 09:17:37AM +0000, Chris Wilson wrote:
> If the initialisation fails, we may be left with a dangling pointer with
> an incomplete fbdev structure.

This shouldn't happen with 4.5, the fbdev is now clobbered if initialization
fails, the existing "if (dev_priv->fbdev)" checks should thus be sufficient.
See 54632abe8ca3 ("drm/i915: Fix oops caused by fbdev initialization
failure") as well as 366e39b4d2c5 ("drm/i915: Tear down fbdev if
initialization fails").

Gustav Fagerlind and Li Weinan both reported this for 4.3. It would be
interesting to know if it can be reproduced at all with 4.5-rc2.

Best regards,

Lukas

> 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 | 41 ++++++++++++++++++++++++--------------
>  1 file changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 09840f4380f9..6218bc5370a1 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -114,6 +114,20 @@ static struct fb_ops intelfb_ops = {
>  	.fb_debug_leave = drm_fb_helper_debug_leave,
>  };
>  
> +static bool intel_fbdev_active(struct intel_fbdev *ifbdev)
> +{
> +	struct fb_info *info;
> +
> +	if (ifbdev == NULL)
> +		return false;
> +
> +	info = ifbdev->helper.fbdev;
> +	if (!info->screen_base)
> +		return false;
> +
> +	return info->state == FBINFO_STATE_RUNNING;
> +}
> +
>  static int intelfb_alloc(struct drm_fb_helper *helper,
>  			 struct drm_fb_helper_surface_size *sizes)
>  {
> @@ -753,6 +767,8 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
>  		return;
>  
>  	info = ifbdev->helper.fbdev;
> +	if (!info->screen_base)
> +		return;
>  
>  	if (synchronous) {
>  		/* Flush any pending work to turn the console on, and then
> @@ -794,29 +810,24 @@ 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;
> -	if (dev_priv->fbdev)
> +	struct drm_i915_private *dev_priv = to_i915(dev);
> +
> +	if (intel_fbdev_active(dev_priv->fbdev))
>  		drm_fb_helper_hotplug_event(&dev_priv->fbdev->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 = to_i915(dev)->fbdev;
>  
> -	if (!ifbdev)
> +	if (!intel_fbdev_active(ifbdev))
>  		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);
> +	} else {
> +		DRM_DEBUG("failed to restore crtc mode\n");
>  	}
>  }
> -- 
> 2.7.0
> 
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