Re: [PATCH 5/5] drm/vblank: Require all CRTCs implement vblank support in drm_vblank_init()
From: sashiko-bot@kernel.org
Date: 2026-08-14 21:08:43
Also in:
dri-devel, imx, intel-gfx, intel-xe, linux-amlogic, linux-sunxi
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [High] drm_vblank_init() causes a NULL pointer dereference or driver probe failure due to accessing uninitialized or empty crtc_list --
--- Patch [5]: [PATCH 5/5] drm/vblank: Require all CRTCs implement vblank support in drm_vblank_init() ---commit 178bbb448a16663eaad60425c62b446801e0f387 Author: Lyude Paul [off-list ref] drm/vblank: Require all CRTCs implement vblank support in drm_vblank_init() This commit modifies drm_vblank_init() to verify that all CRTCs implement vblank support, ensuring an all-or-nothing configuration. It returns -EINVAL if support is mixed, and -ENODEV if no CRTCs support vblank.
quoted hunk ↗ jump to hunk
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index d57405050554f..17affae23e7a6 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c@@ -542,12 +542,31 @@ static void drm_vblank_init_release(struct drm_device *dev, void *ptr) * drmm_add_action_or_reset(). * * Returns: - * Zero on success or a negative error code on failure. + * Zero on success or a negative error code on failure. If no CRTCs with vblank + * support implemented were found, -ENODEV will be returned. */ int drm_vblank_init(struct drm_device *dev) { int ret; struct drm_crtc *crtc; + bool found_vbl_crtc = false, found_non_vbl_crtc = false; + + /* Vblank hooks are per-CRTC, not per-device - which is contrary to how + * the vblank core was written. Since hardware that only has vblank + * support on some CRTCs but not all is non-existent and would likely + * lead to UB, ensure that vblank support is all or nothing. + */ + drm_for_each_crtc(crtc, dev) {
[Severity: High] Can iterating over dev->mode_config.crtc_list here cause a NULL pointer dereference or a false -ENODEV return during driver probe? Several DRM drivers call drm_vblank_init() before initializing mode_config or creating CRTCs. For example: In i915, intel_display_driver_probe_noirq() calls drm_vblank_init() before intel_mode_config_init() sets up the crtc_list, meaning the list head is uninitialized. In vkms, vkms_create() calls drm_vblank_init() before vkms_modeset_init() initializes the crtc_list. In zynqmp_kms, zynqmp_dpsub_drm_init() initializes the list but calls drm_vblank_init() before any CRTCs are created, meaning the list is empty and this function will unconditionally return -ENODEV. Does drm_vblank_init() need to support being called before CRTCs are registered?
+ if (crtc->funcs->enable_vblank) + found_vbl_crtc = true; + else + found_non_vbl_crtc = true; + + if (drm_WARN_ON(dev, found_vbl_crtc && found_non_vbl_crtc)) + return -EINVAL; + } + if (!found_vbl_crtc) + return -ENODEV;
-- Sashiko AI review · https://sashiko.dev/#/patchset/20260814203542.1405135-1-lyude@redhat.com?part=5