[PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Tim Gardner]

smatch warning:

drivers/gpu/drm/i915/intel_display.c:7019 intel_set_mode() warn: function puts
500 bytes on stack

Refactor so that saved_mode and saved_hwmode are dynamically allocated as opposed
to being automatic variables. 500 bytes seems like it could run the potential for blowing
the kernel stack, especially if struct drm_display_mode ever grows significantly.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 drivers/gpu/drm/i915/intel_display.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index de51489..f8754d6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7739,11 +7739,18 @@ bool intel_set_mode(struct drm_crtc *crtc,
 {
 	struct drm_device *dev = crtc->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
-	struct drm_display_mode *adjusted_mode, saved_mode, saved_hwmode;
+	struct drm_display_mode *adjusted_mode, *saved_mode, *saved_hwmode;
 	struct intel_crtc *intel_crtc;
 	unsigned disable_pipes, prepare_pipes, modeset_pipes;
 	bool ret = true;
 
+	saved_mode = kmalloc(2*sizeof(*saved_mode), GFP_KERNEL);
+	if (!saved_mode) {
+		pr_err("i915: Could not allocate saved display mode.\n");
+		return false;
+	}
+	saved_hwmode = saved_mode + 1;
+
 	intel_modeset_affected_pipes(crtc, &modeset_pipes,
 				     &prepare_pipes, &disable_pipes);
 
@@ -7753,8 +7760,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
 	for_each_intel_crtc_masked(dev, disable_pipes, intel_crtc)
 		intel_crtc_disable(&intel_crtc->base);
 
-	saved_hwmode = crtc->hwmode;
-	saved_mode = crtc->mode;
+	*saved_hwmode = crtc->hwmode;
+	*saved_mode = crtc->mode;
 
 	/* Hack: Because we don't (yet) support global modeset on multiple
 	 * crtcs, we don't keep track of the new mode for more than one crtc.
@@ -7817,12 +7824,13 @@ bool intel_set_mode(struct drm_crtc *crtc,
 done:
 	drm_mode_destroy(dev, adjusted_mode);
 	if (!ret && crtc->enabled) {
-		crtc->hwmode = saved_hwmode;
-		crtc->mode = saved_mode;
+		crtc->hwmode = *saved_hwmode;
+		crtc->mode = *saved_mode;
 	} else {
 		intel_modeset_check_state(dev);
 	}
 
+	kfree(saved_mode);
 	return ret;
 }
 
-- 
1.7.9.5

Re: [PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Jani Nikula]

On Thu, 06 Dec 2012, Tim Gardner <tim.gardner@canonical.com> wrote:
> smatch warning:
>
> drivers/gpu/drm/i915/intel_display.c:7019 intel_set_mode() warn: function puts
> 500 bytes on stack
>
> Refactor so that saved_mode and saved_hwmode are dynamically allocated as opposed
> to being automatic variables. 500 bytes seems like it could run the potential for blowing
> the kernel stack, especially if struct drm_display_mode ever grows significantly.

Hi Tim, seems reasonable, but please find a few comments inline.

BR,
Jani.

>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@linux.ie>
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c |   18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index de51489..f8754d6 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -7739,11 +7739,18 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  {
>  	struct drm_device *dev = crtc->dev;
>  	drm_i915_private_t *dev_priv = dev->dev_private;
> -	struct drm_display_mode *adjusted_mode, saved_mode, saved_hwmode;
> +	struct drm_display_mode *adjusted_mode, *saved_mode, *saved_hwmode;
>  	struct intel_crtc *intel_crtc;
>  	unsigned disable_pipes, prepare_pipes, modeset_pipes;
>  	bool ret = true;
>  
> +	saved_mode = kmalloc(2*sizeof(*saved_mode), GFP_KERNEL);

Style nitpick, missing spaces around the first *.

> +	if (!saved_mode) {
> +		pr_err("i915: Could not allocate saved display mode.\n");

Please use DRM_ERROR().

> +		return false;
> +	}
> +	saved_hwmode = saved_mode + 1;
> +
>  	intel_modeset_affected_pipes(crtc, &modeset_pipes,
>  				     &prepare_pipes, &disable_pipes);
>  
> @@ -7753,8 +7760,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  	for_each_intel_crtc_masked(dev, disable_pipes, intel_crtc)
>  		intel_crtc_disable(&intel_crtc->base);
>  
> -	saved_hwmode = crtc->hwmode;
> -	saved_mode = crtc->mode;
> +	*saved_hwmode = crtc->hwmode;
> +	*saved_mode = crtc->mode;
>  
>  	/* Hack: Because we don't (yet) support global modeset on multiple
>  	 * crtcs, we don't keep track of the new mode for more than one crtc.

You are missing a kfree in the adjusted_mode error path after this hunk.

> @@ -7817,12 +7824,13 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  done:
>  	drm_mode_destroy(dev, adjusted_mode);
>  	if (!ret && crtc->enabled) {
> -		crtc->hwmode = saved_hwmode;
> -		crtc->mode = saved_mode;
> +		crtc->hwmode = *saved_hwmode;
> +		crtc->mode = *saved_mode;
>  	} else {
>  		intel_modeset_check_state(dev);
>  	}
>  
> +	kfree(saved_mode);
>  	return ret;
>  }
>  
> -- 
> 1.7.9.5
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Chris Wilson]

On Fri, 07 Dec 2012 13:47:46 +0200, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> 
> On Thu, 06 Dec 2012, Tim Gardner <tim.gardner@canonical.com> wrote:
> > +	if (!saved_mode) {
> > +		pr_err("i915: Could not allocate saved display mode.\n");
> 
> Please use DRM_ERROR().

Truthfully neither, but join the growing petition to get real errorcodes
back to userspace!
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Jani Nikula]

On Fri, 07 Dec 2012, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> On Fri, 07 Dec 2012 13:47:46 +0200, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>> 
>> On Thu, 06 Dec 2012, Tim Gardner <tim.gardner@canonical.com> wrote:
>> > +	if (!saved_mode) {
>> > +		pr_err("i915: Could not allocate saved display mode.\n");
>> 
>> Please use DRM_ERROR().
>
> Truthfully neither, but join the growing petition to get real errorcodes
> back to userspace!

Heh, agreed, but in the mean time (i.e. before hell freezes over) I
think we should prefer DRM_ERROR over pr_err for consistency.

Jani.

[PATCH v2 linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Tim Gardner]

smatch warning:

drivers/gpu/drm/i915/intel_display.c:7019 intel_set_mode() warn: function puts
500 bytes on stack

Refactor so that saved_mode and saved_hwmode are dynamically allocated as opposed
to being automatic variables. 500 bytes seems like it could run the potential for blowing
the kernel stack.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---

V2 - spaces around '*', use kmalloc instead of kzalloc(). Missed
error return that would have orphaned memory.

 drivers/gpu/drm/i915/intel_display.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index de51489..c15b21b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7739,11 +7739,18 @@ bool intel_set_mode(struct drm_crtc *crtc,
 {
 	struct drm_device *dev = crtc->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
-	struct drm_display_mode *adjusted_mode, saved_mode, saved_hwmode;
+	struct drm_display_mode *adjusted_mode, *saved_mode, *saved_hwmode;
 	struct intel_crtc *intel_crtc;
 	unsigned disable_pipes, prepare_pipes, modeset_pipes;
 	bool ret = true;
 
+	saved_mode = kmalloc(2 * sizeof(*saved_mode), GFP_KERNEL);
+	if (!saved_mode) {
+		DRM_ERROR("i915: Could not allocate saved display mode.\n");
+		return false;
+	}
+	saved_hwmode = saved_mode + 1;
+
 	intel_modeset_affected_pipes(crtc, &modeset_pipes,
 				     &prepare_pipes, &disable_pipes);
 
@@ -7753,8 +7760,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
 	for_each_intel_crtc_masked(dev, disable_pipes, intel_crtc)
 		intel_crtc_disable(&intel_crtc->base);
 
-	saved_hwmode = crtc->hwmode;
-	saved_mode = crtc->mode;
+	*saved_hwmode = crtc->hwmode;
+	*saved_mode = crtc->mode;
 
 	/* Hack: Because we don't (yet) support global modeset on multiple
 	 * crtcs, we don't keep track of the new mode for more than one crtc.
@@ -7765,7 +7772,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
 	if (modeset_pipes) {
 		adjusted_mode = intel_modeset_adjusted_mode(crtc, mode);
 		if (IS_ERR(adjusted_mode)) {
-			return false;
+			ret = false;
+			goto out;
 		}
 	}
 
@@ -7817,12 +7825,14 @@ bool intel_set_mode(struct drm_crtc *crtc,
 done:
 	drm_mode_destroy(dev, adjusted_mode);
 	if (!ret && crtc->enabled) {
-		crtc->hwmode = saved_hwmode;
-		crtc->mode = saved_mode;
+		crtc->hwmode = *saved_hwmode;
+		crtc->mode = *saved_mode;
 	} else {
 		intel_modeset_check_state(dev);
 	}
 
+out:
+	kfree(saved_mode);
 	return ret;
 }
 
-- 
1.7.9.5

Re: [PATCH v2 linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Jani Nikula]

On Fri, 07 Dec 2012, Tim Gardner <tim.gardner@canonical.com> wrote:
> smatch warning:
>
> drivers/gpu/drm/i915/intel_display.c:7019 intel_set_mode() warn: function puts
> 500 bytes on stack
>
> Refactor so that saved_mode and saved_hwmode are dynamically allocated as opposed
> to being automatic variables. 500 bytes seems like it could run the potential for blowing
> the kernel stack.

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


>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@linux.ie>
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
> ---
>
> V2 - spaces around '*', use kmalloc instead of kzalloc(). Missed
> error return that would have orphaned memory.
>
>  drivers/gpu/drm/i915/intel_display.c |   22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index de51489..c15b21b 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -7739,11 +7739,18 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  {
>  	struct drm_device *dev = crtc->dev;
>  	drm_i915_private_t *dev_priv = dev->dev_private;
> -	struct drm_display_mode *adjusted_mode, saved_mode, saved_hwmode;
> +	struct drm_display_mode *adjusted_mode, *saved_mode, *saved_hwmode;
>  	struct intel_crtc *intel_crtc;
>  	unsigned disable_pipes, prepare_pipes, modeset_pipes;
>  	bool ret = true;
>  
> +	saved_mode = kmalloc(2 * sizeof(*saved_mode), GFP_KERNEL);
> +	if (!saved_mode) {
> +		DRM_ERROR("i915: Could not allocate saved display mode.\n");
> +		return false;
> +	}
> +	saved_hwmode = saved_mode + 1;
> +
>  	intel_modeset_affected_pipes(crtc, &modeset_pipes,
>  				     &prepare_pipes, &disable_pipes);
>  
> @@ -7753,8 +7760,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  	for_each_intel_crtc_masked(dev, disable_pipes, intel_crtc)
>  		intel_crtc_disable(&intel_crtc->base);
>  
> -	saved_hwmode = crtc->hwmode;
> -	saved_mode = crtc->mode;
> +	*saved_hwmode = crtc->hwmode;
> +	*saved_mode = crtc->mode;
>  
>  	/* Hack: Because we don't (yet) support global modeset on multiple
>  	 * crtcs, we don't keep track of the new mode for more than one crtc.
> @@ -7765,7 +7772,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  	if (modeset_pipes) {
>  		adjusted_mode = intel_modeset_adjusted_mode(crtc, mode);
>  		if (IS_ERR(adjusted_mode)) {
> -			return false;
> +			ret = false;
> +			goto out;
>  		}
>  	}
>  
> @@ -7817,12 +7825,14 @@ bool intel_set_mode(struct drm_crtc *crtc,
>  done:
>  	drm_mode_destroy(dev, adjusted_mode);
>  	if (!ret && crtc->enabled) {
> -		crtc->hwmode = saved_hwmode;
> -		crtc->mode = saved_mode;
> +		crtc->hwmode = *saved_hwmode;
> +		crtc->mode = *saved_mode;
>  	} else {
>  		intel_modeset_check_state(dev);
>  	}
>  
> +out:
> +	kfree(saved_mode);
>  	return ret;
>  }
>  
> -- 
> 1.7.9.5

Re: [PATCH v2 linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers

[Daniel Vetter]

On Mon, Dec 10, 2012 at 09:29:17AM +0200, Jani Nikula wrote:
> On Fri, 07 Dec 2012, Tim Gardner <tim.gardner@canonical.com> wrote:
> > smatch warning:
> >
> > drivers/gpu/drm/i915/intel_display.c:7019 intel_set_mode() warn: function puts
> > 500 bytes on stack
> >
> > Refactor so that saved_mode and saved_hwmode are dynamically allocated as opposed
> > to being automatic variables. 500 bytes seems like it could run the potential for blowing
> > the kernel stack.
> 
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch