[PATCH V3] drm_crtc: check if fb_create return NULL

[PATCH V3] drm_crtc: check if fb_create return NULL

[Su, Xuemin]

From: xueminsu <xuemin.su@intel.com>
Date: Tue, 22 Jan 2013 22:39:39 +0800
Subject: [PATCH] drm_crtc: check if fb_create return NULL

Some buggy driver may still return NULL in fb_create,
which leads to kernel panic.

Signed-off-by: xueminsu <xuemin.su@intel.com>
---
 drivers/gpu/drm/drm_crtc.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index f2d667b..ae613ec 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -2172,6 +2172,8 @@ int drm_mode_addfb(struct drm_device *dev,
 		ret = PTR_ERR(fb);
 		goto out;
 	}
+	/* some buggy driver may return NULL here, which may cause panic */
+	BUG_ON(!fb);
 
 	or->fb_id = fb->base.id;
 	list_add(&fb->filp_head, &file_priv->fbs);
-- 
1.7.6

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Jani Nikula]

On Thu, 24 Jan 2013, "Su, Xuemin" <xuemin.su@intel.com> wrote:
> From: xueminsu <xuemin.su@intel.com>
> Date: Tue, 22 Jan 2013 22:39:39 +0800
> Subject: [PATCH] drm_crtc: check if fb_create return NULL
>
> Some buggy driver may still return NULL in fb_create,
> which leads to kernel panic.
>
> Signed-off-by: xueminsu <xuemin.su@intel.com>
> ---
>  drivers/gpu/drm/drm_crtc.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index f2d667b..ae613ec 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -2172,6 +2172,8 @@ int drm_mode_addfb(struct drm_device *dev,
>  		ret = PTR_ERR(fb);
>  		goto out;
>  	}
> +	/* some buggy driver may return NULL here, which may cause panic */
> +	BUG_ON(!fb);

I fail to see the benefit of this compared to just letting it oops...

>  	or->fb_id = fb->base.id;

...right here.


BR,
Jani.

>  	list_add(&fb->filp_head, &file_priv->fbs);
> -- 
> 1.7.6
>
>
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Jani Nikula]

On Thu, 24 Jan 2013, "Su, Xuemin" <xuemin.su@intel.com> wrote:
> From: xueminsu <xuemin.su@intel.com>
> Date: Tue, 22 Jan 2013 22:39:39 +0800
> Subject: [PATCH] drm_crtc: check if fb_create return NULL
>
> Some buggy driver may still return NULL in fb_create,
> which leads to kernel panic.
>
> Signed-off-by: xueminsu <xuemin.su@intel.com>
> ---
>  drivers/gpu/drm/drm_crtc.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index f2d667b..ae613ec 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -2172,6 +2172,8 @@ int drm_mode_addfb(struct drm_device *dev,
>  		ret = PTR_ERR(fb);
>  		goto out;
>  	}
> +	/* some buggy driver may return NULL here, which may cause panic */
> +	BUG_ON(!fb);

I fail to see the benefit of this compared to just letting it oops...

>  	or->fb_id = fb->base.id;

...right here.


BR,
Jani.

>  	list_add(&fb->filp_head, &file_priv->fbs);
> -- 
> 1.7.6
>
>
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Su, Xuemin]

On Thu, 2013-01-24 at 10:31 +0200, Jani Nikula wrote:
> >  	}
> > +	/* some buggy driver may return NULL here, which may cause panic */
> > +	BUG_ON(!fb);
> 
> I fail to see the benefit of this compared to just letting it oops...
> 
> >  	or->fb_id = fb->base.id;
> 
> ...right here.
> 
> 
For PATCH V3, I think a BUG_ON may give the user clearer information
about the reason of panic. Easier to debug.
I submitted a PATCH V2 yesterday which gives a warning and then return
-EVAL if fb==NULL, preventing the panic. Do you think this is
acceptable?

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Jani Nikula]

On Thu, 24 Jan 2013, "Su, Xuemin" <xuemin.su@intel.com> wrote:
> On Thu, 2013-01-24 at 10:31 +0200, Jani Nikula wrote:
>> >  	}
>> > +	/* some buggy driver may return NULL here, which may cause panic */
>> > +	BUG_ON(!fb);
>> 
>> I fail to see the benefit of this compared to just letting it oops...
>> 
>> >  	or->fb_id = fb->base.id;
>> 
>> ...right here.
>> 
>> 
> For PATCH V3, I think a BUG_ON may give the user clearer information
> about the reason of panic. Easier to debug.

Ah, sorry, never mind, I missed Daniel's comment. The benefit of the
BUG_ON() is making it clear what's expected of the drivers.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Jani Nikula]

On Thu, 24 Jan 2013, "Su, Xuemin" <xuemin.su@intel.com> wrote:
> On Thu, 2013-01-24 at 10:31 +0200, Jani Nikula wrote:
>> >  	}
>> > +	/* some buggy driver may return NULL here, which may cause panic */
>> > +	BUG_ON(!fb);
>> 
>> I fail to see the benefit of this compared to just letting it oops...
>> 
>> >  	or->fb_id = fb->base.id;
>> 
>> ...right here.
>> 
>> 
> For PATCH V3, I think a BUG_ON may give the user clearer information
> about the reason of panic. Easier to debug.

Ah, sorry, never mind, I missed Daniel's comment. The benefit of the
BUG_ON() is making it clear what's expected of the drivers.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

RE: [PATCH V3] drm_crtc: check if fb_create return NULL

[Su, Xuemin]

-----Original Message-----
From: Jani Nikula [mailto:jani.nikula@linux.intel.com] 
Sent: Thursday, January 24, 2013 5:05 PM
To: Su, Xuemin
Cc: airlied@linux.ie; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; yanmin_zhang@linux.intel.com; He, Bo
Subject: Re: [PATCH V3] drm_crtc: check if fb_create return NULL

>Ah, sorry, never mind, I missed Daniel's comment. The benefit of the
>BUG_ON() is making it clear what's expected of the drivers.

>Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Do you think this patch is still needed?
Currently I fix a buggy function radeon_user_framebuffer_create() which returns NULL and patch is added to 3.7-stable tree.
Do you think it's also needed to do something in drm_mode_addfb()?
Thanks.

Re: [PATCH V3] drm_crtc: check if fb_create return NULL

[Daniel Vetter]

On Thu, Jan 31, 2013 at 1:55 AM, Su, Xuemin <xuemin.su@intel.com> wrote:
> -----Original Message-----
> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
> Sent: Thursday, January 24, 2013 5:05 PM
> To: Su, Xuemin
> Cc: airlied@linux.ie; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; yanmin_zhang@linux.intel.com; He, Bo
> Subject: Re: [PATCH V3] drm_crtc: check if fb_create return NULL
>
>>Ah, sorry, never mind, I missed Daniel's comment. The benefit of the
>>BUG_ON() is making it clear what's expected of the drivers.
>
>>Reviewed-by: Jani Nikula <jani.nikula@intel.com>
>
> Do you think this patch is still needed?
> Currently I fix a buggy function radeon_user_framebuffer_create() which returns NULL and patch is added to 3.7-stable tree.
> Do you think it's also needed to do something in drm_mode_addfb()?

Imo it's still useful, just to document the assumptions of the interface. Dave?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch