Re: [PATCH v3 2/2] drm/i915: Fix oops caused by fbdev initialization failure

[Lukas Wunner <lukas@wunner.de>]

Hi,

On Thu, Nov 19, 2015 at 05:02:04PM +0100, Daniel Vetter wrote:
> On Wed, Nov 18, 2015 at 01:43:20PM +0100, Lukas Wunner wrote:
> > intelfb_create() is called once on driver initialization. If it fails,
> > ifbdev->helper.fbdev, ifbdev->fb or ifbdev->fb->obj may be NULL.
> > 
> > Further up in the call stack, intel_fbdev_initial_config() calls
> > intel_fbdev_fini() to tear down the ifbdev on failure. This calls
> > intel_fbdev_destroy() which dereferences ifbdev->fb. Fix the ensuing
> > oops.
> > 
> > Also check in these functions if ifbdev is not NULL to avoid oops:
> > 
> > i915_gem_framebuffer_info() is called on access to debugfs file
> > "i915_gem_framebuffer" and dereferences ifbdev, ifbdev->helper.fb
> > and ifbdev->helper.fb->obj.
> > 
> > intel_connector_add_to_fbdev() / intel_connector_remove_from_fbdev()
> > are called when registering / unregistering an mst connector and
> > dereference ifbdev.
> > 
> > v3: Drop additional null pointer checks in intel_fbdev_set_suspend(),
> >     intel_fbdev_output_poll_changed() and intel_fbdev_restore_mode()
> >     since they already check if ifbdev is not NULL, which is sufficient
> >     now that intel_fbdev_fini() is called on initialization failure.
> >     (Requested by Daniel Vetter <daniel.vetter@ffwll.ch>)
> > 
> > Signed-off-by: Lukas Wunner <lukas@wunner.de>
> 
> Queued for -next, thanks for the patch. Aside, with this patch and the
> static inline dummies from Archit I think we can drop most of the #ifdef
> blocks (not the one in debugfs though). Care for a follow-up patch to
> remove them around add/remove_one_connector?

Will do, I actually did check if they are obsolete now but thought they are
not because the functions are in drm_fb_helper.c which is only compiled if
CONFIG_DRM_FBDEV_EMULATION is defined. I simply forgot to check if there
are static inlines.

Thanks,

Lukas

> -Daniel
> > ---
> >  drivers/gpu/drm/i915/i915_debugfs.c | 24 +++++++++++++-----------
> >  drivers/gpu/drm/i915/intel_dp_mst.c | 10 ++++++++--
> >  drivers/gpu/drm/i915/intel_fbdev.c  |  6 ++++--
> >  3 files changed, 25 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 038d5c6..411a9c6 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -1877,17 +1877,19 @@ static int i915_gem_framebuffer_info(struct seq_file *m, void *data)
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  
> >  	ifbdev = dev_priv->fbdev;
> > -	fb = to_intel_framebuffer(ifbdev->helper.fb);
> > -
> > -	seq_printf(m, "fbcon size: %d x %d, depth %d, %d bpp, modifier 0x%llx, refcount %d, obj ",
> > -		   fb->base.width,
> > -		   fb->base.height,
> > -		   fb->base.depth,
> > -		   fb->base.bits_per_pixel,
> > -		   fb->base.modifier[0],
> > -		   atomic_read(&fb->base.refcount.refcount));
> > -	describe_obj(m, fb->obj);
> > -	seq_putc(m, '\n');
> > +	if (ifbdev) {
> > +		fb = to_intel_framebuffer(ifbdev->helper.fb);
> > +
> > +		seq_printf(m, "fbcon size: %d x %d, depth %d, %d bpp, modifier 0x%llx, refcount %d, obj ",
> > +			   fb->base.width,
> > +			   fb->base.height,
> > +			   fb->base.depth,
> > +			   fb->base.bits_per_pixel,
> > +			   fb->base.modifier[0],
> > +			   atomic_read(&fb->base.refcount.refcount));
> > +		describe_obj(m, fb->obj);
> > +		seq_putc(m, '\n');
> > +	}
> >  #endif
> >  
> >  	mutex_lock(&dev->mode_config.fb_lock);
> > diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> > index 9d8a5b4..8c4e7df 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > @@ -408,7 +408,10 @@ static void intel_connector_add_to_fbdev(struct intel_connector *connector)
> >  {
> >  #ifdef CONFIG_DRM_FBDEV_EMULATION
> >  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> > -	drm_fb_helper_add_one_connector(&dev_priv->fbdev->helper, &connector->base);
> > +
> > +	if (dev_priv->fbdev)
> > +		drm_fb_helper_add_one_connector(&dev_priv->fbdev->helper,
> > +						&connector->base);
> >  #endif
> >  }
> >  
> > @@ -416,7 +419,10 @@ static void intel_connector_remove_from_fbdev(struct intel_connector *connector)
> >  {
> >  #ifdef CONFIG_DRM_FBDEV_EMULATION
> >  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> > -	drm_fb_helper_remove_one_connector(&dev_priv->fbdev->helper, &connector->base);
> > +
> > +	if (dev_priv->fbdev)
> > +		drm_fb_helper_remove_one_connector(&dev_priv->fbdev->helper,
> > +						   &connector->base);
> >  #endif
> >  }
> >  
> > diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> > index cd345c5..7ccde58 100644
> > --- a/drivers/gpu/drm/i915/intel_fbdev.c
> > +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> > @@ -530,8 +530,10 @@ static void intel_fbdev_destroy(struct drm_device *dev,
> >  
> >  	drm_fb_helper_fini(&ifbdev->helper);
> >  
> > -	drm_framebuffer_unregister_private(&ifbdev->fb->base);
> > -	drm_framebuffer_remove(&ifbdev->fb->base);
> > +	if (ifbdev->fb) {
> > +		drm_framebuffer_unregister_private(&ifbdev->fb->base);
> > +		drm_framebuffer_remove(&ifbdev->fb->base);
> > +	}
> >  }
> >  
> >  /*
> > -- 
> > 2.1.0
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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