drm/vmwgfx: Don't double-free the mode stored in par->set_mode

BugLink: https://bugs.launchpad.net/bugs/1826212

commit c2d31155 upstream.

When calling vmw_fb_set_par(), the mode stored in par->set_mode gets free'd
twice. The first free is in vmw_fb_kms_detach(), the second is near the
end of vmw_fb_set_par() under the name of 'old_mode'. The mode-setting code
only works correctly if the mode doesn't actually change. Removing
'old_mode' in favor of using par->set_mode directly fixes the problem.

Cc: <stable@vger.kernel.org>
Fixes: a278724a ("drm/vmwgfx: Implement fbdev on kms v2")
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Deepak Rawat <drawat@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/gpu/drm/vmwgfx/vmwgfx_fb.c

@@ -531,11 +531,9 @@ static int vmw_fb_set_par(struct fb_info *info)
 		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 		DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_PVSYNC)
 	};
-	struct drm_display_mode *old_mode;
 	struct drm_display_mode *mode;
 	int ret;
 
-	old_mode = par->set_mode;
 	mode = drm_mode_duplicate(vmw_priv->dev, &new_mode);
 	if (!mode) {
 		DRM_ERROR("Could not create new fb mode.\n");
@@ -546,11 +544,7 @@ static int vmw_fb_set_par(struct fb_info *info)
 	mode->vdisplay = var->yres;
 	vmw_guess_mode_timing(mode);
 
-	if (old_mode && drm_mode_equal(old_mode, mode)) {
-		drm_mode_destroy(vmw_priv->dev, mode);
-		mode = old_mode;
-		old_mode = NULL;
-	} else if (!vmw_kms_validate_mode_vram(vmw_priv,
+	if (!vmw_kms_validate_mode_vram(vmw_priv,
 					mode->hdisplay *
 					DIV_ROUND_UP(var->bits_per_pixel, 8),
 					mode->vdisplay)) {
@@ -613,8 +607,8 @@ static int vmw_fb_set_par(struct fb_info *info)
 	schedule_delayed_work(&par->local_work, 0);
 
 out_unlock:
-	if (old_mode)
-		drm_mode_destroy(vmw_priv->dev, old_mode);
+	if (par->set_mode)
+		drm_mode_destroy(vmw_priv->dev, par->set_mode);
 	par->set_mode = mode;
 
 	drm_modeset_unlock_all(vmw_priv->dev);