[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 at ffwll.ch>
Cc: David Airlie <airlied at linux.ie>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Tim Gardner <tim.gardner at 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