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Message-ID: <87zk1qm6cd.fsf@intel.com>
Date: Fri, 07 Dec 2012 13:47:46 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Tim Gardner <tim.gardner@...onical.com>,
linux-kernel@...r.kernel.org
Cc: Daniel Vetter <daniel.vetter@...ll.ch>,
Tim Gardner <tim.gardner@...onical.com>,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH linux-next] i915: intel_set_mode: Reduce stack allocation from 500 bytes to 2 pointers
On Thu, 06 Dec 2012, Tim Gardner <tim.gardner@...onical.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@...ll.ch>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Tim Gardner <tim.gardner@...onical.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@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
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