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  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 
Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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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  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 


>
> Cc: Daniel Vetter 
> Cc: David Airlie 
> Cc: dri-de...@lists.freedesktop.org
> Signed-off-by: Tim Gardner 
> ---
>
> 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
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[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 
Cc: David Airlie 
Cc: dri-de...@lists.freedesktop.org
Signed-off-by: Tim Gardner 
---

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

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