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Sun, 01 Feb 2026 02:00:10 -0800 (PST) From: Shenghao Yang To: Ruben Wauters , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Shenghao Yang , stable+noautosel@kernel.org, kernel test robot , Dan Carpenter Subject: [PATCH v2] drm/gud: fix NULL crtc dereference on display disable Date: Sun, 1 Feb 2026 17:59:56 +0800 Message-ID: <20260201095956.21042-1-me@shenghaoyang.info> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" gud_plane_atomic_update() currently handles both crtc state and framebuffer updates - the complexity has led to a few accidental NULL pointer dereferences. Commit dc2d5ddb193e ("drm/gud: fix NULL fb and crtc dereferences on USB disconnect") [1] fixed an earlier dereference but planes can also be disabled in non-hotplug paths (e.g. display disables via the desktop environment). The drm_dev_enter() call would not cause an early return in those and subsequently oops on dereferencing crtc: BUG: kernel NULL pointer dereference, address: 00000000000005c8 CPU: 6 UID: 1000 PID: 3473 Comm: kwin_wayland Not tainted 6.18.2-200.vanill= a.gud.fc42.x86_64 #1 PREEMPT(lazy) RIP: 0010:gud_plane_atomic_update+0x148/0x470 [gud] drm_atomic_helper_commit_planes+0x28e/0x310 drm_atomic_helper_commit_tail+0x2a/0x70 commit_tail+0xf1/0x150 drm_atomic_helper_commit+0x13c/0x180 drm_atomic_commit+0xb1/0xe0 info ? __pfx___drm_printfn_info+0x10/0x10 drm_mode_atomic_ioctl+0x70f/0x7c0 ? __pfx_drm_mode_atomic_ioctl+0x10/0x10 drm_ioctl_kernel+0xae/0x100 drm_ioctl+0x2a8/0x550 ? __pfx_drm_mode_atomic_ioctl+0x10/0x10 __x64_sys_ioctl+0x97/0xe0 do_syscall_64+0x7e/0x7f0 ? __ct_user_enter+0x56/0xd0 ? do_syscall_64+0x158/0x7f0 ? __ct_user_enter+0x56/0xd0 ? do_syscall_64+0x158/0x7f0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Split out crtc handling from gud_plane_atomic_update() into atomic_enable() and atomic_disable() functions to delegate crtc state transitioning work to the DRM helpers. To preserve the gud state commit sequence [2], switch to the runtime PM version of drm_atomic_helper_commit_tail() which ensures that crtcs are enabled (hence sending the GUD_REQ_SET_CONTROLLER_ENABLE and GUD_REQ_SET_DISPLAY_ENABLE requests) before a framebuffer update is sent. [1] https://lore.kernel.org/all/20251231055039.44266-1-me@shenghaoyang.info/ [2] https://github.com/notro/gud/wiki/GUD-Protocol#display-state Cc: # won't apply cleanly on 6.18.x Reported-by: kernel test robot Reported-by: Dan Carpenter Closes: https://lore.kernel.org/r/202601142159.0v8ilfVs-lkp@intel.com/ Fixes: 73cfd166e045 ("drm/gud: Replace simple display pipe with DRM atomic = helpers") Signed-off-by: Shenghao Yang --- drivers/gpu/drm/gud/gud_drv.c | 9 ++++- drivers/gpu/drm/gud/gud_internal.h | 4 ++ drivers/gpu/drm/gud/gud_pipe.c | 59 +++++++++++++++++++++--------- 3 files changed, 53 insertions(+), 19 deletions(-) diff --git a/drivers/gpu/drm/gud/gud_drv.c b/drivers/gpu/drm/gud/gud_drv.c index 42135a48d92e..a2000991ecbe 100644 --- a/drivers/gpu/drm/gud/gud_drv.c +++ b/drivers/gpu/drm/gud/gud_drv.c @@ -339,7 +339,9 @@ static int gud_stats_debugfs(struct seq_file *m, void *= data) } =20 static const struct drm_crtc_helper_funcs gud_crtc_helper_funcs =3D { - .atomic_check =3D drm_crtc_helper_atomic_check + .atomic_check =3D drm_crtc_helper_atomic_check, + .atomic_enable =3D gud_crtc_atomic_enable, + .atomic_disable =3D gud_crtc_atomic_disable, }; =20 static const struct drm_crtc_funcs gud_crtc_funcs =3D { @@ -364,6 +366,10 @@ static const struct drm_plane_funcs gud_plane_funcs = =3D { DRM_GEM_SHADOW_PLANE_FUNCS, }; =20 +static const struct drm_mode_config_helper_funcs gud_mode_config_helpers = =3D { + .atomic_commit_tail =3D drm_atomic_helper_commit_tail_rpm, +}; + static const struct drm_mode_config_funcs gud_mode_config_funcs =3D { .fb_create =3D drm_gem_fb_create_with_dirty, .atomic_check =3D drm_atomic_helper_check, @@ -499,6 +505,7 @@ static int gud_probe(struct usb_interface *intf, const = struct usb_device_id *id) drm->mode_config.min_height =3D le32_to_cpu(desc.min_height); drm->mode_config.max_height =3D le32_to_cpu(desc.max_height); drm->mode_config.funcs =3D &gud_mode_config_funcs; + drm->mode_config.helper_private =3D &gud_mode_config_helpers; =20 /* Format init */ formats_dev =3D devm_kmalloc(dev, GUD_FORMATS_MAX_NUM, GFP_KERNEL); diff --git a/drivers/gpu/drm/gud/gud_internal.h b/drivers/gpu/drm/gud/gud_i= nternal.h index d27c31648341..a5b7e53cf79c 100644 --- a/drivers/gpu/drm/gud/gud_internal.h +++ b/drivers/gpu/drm/gud/gud_internal.h @@ -62,6 +62,10 @@ int gud_usb_set_u8(struct gud_device *gdrm, u8 request, = u8 val); =20 void gud_clear_damage(struct gud_device *gdrm); void gud_flush_work(struct work_struct *work); +void gud_crtc_atomic_enable(struct drm_crtc *crtc, + struct drm_atomic_state *state); +void gud_crtc_atomic_disable(struct drm_crtc *crtc, + struct drm_atomic_state *state); int gud_plane_atomic_check(struct drm_plane *plane, struct drm_atomic_state *state); void gud_plane_atomic_update(struct drm_plane *plane, diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c index 4b77be94348d..46b47452b315 100644 --- a/drivers/gpu/drm/gud/gud_pipe.c +++ b/drivers/gpu/drm/gud/gud_pipe.c @@ -580,6 +580,44 @@ int gud_plane_atomic_check(struct drm_plane *plane, return ret; } =20 +void gud_crtc_atomic_enable(struct drm_crtc *crtc, + struct drm_atomic_state *state) +{ + struct drm_device *drm =3D crtc->dev; + struct gud_device *gdrm =3D to_gud_device(drm); + int idx; + + if (!drm_dev_enter(drm, &idx)) + return; + + if (crtc->state->mode_changed || crtc->state->connectors_changed) { + gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 1); + gud_usb_set(gdrm, GUD_REQ_SET_STATE_COMMIT, 0, NULL, 0); + } + + gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, crtc->state->active); + + drm_dev_exit(idx); +} + +void gud_crtc_atomic_disable(struct drm_crtc *crtc, + struct drm_atomic_state *state) +{ + struct drm_device *drm =3D crtc->dev; + struct gud_device *gdrm =3D to_gud_device(drm); + int idx; + + if (!drm_dev_enter(drm, &idx)) + return; + + gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, 0); + + if (crtc->state->mode_changed || crtc->state->connectors_changed) + gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0); + + drm_dev_exit(idx); +} + void gud_plane_atomic_update(struct drm_plane *plane, struct drm_atomic_state *atomic_state) { @@ -607,24 +645,12 @@ void gud_plane_atomic_update(struct drm_plane *plane, mutex_unlock(&gdrm->damage_lock); } =20 - if (!drm_dev_enter(drm, &idx)) + if (!crtc || !drm_dev_enter(drm, &idx)) return; =20 - if (!old_state->fb) - gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 1); - - if (fb && (crtc->state->mode_changed || crtc->state->connectors_changed)) - gud_usb_set(gdrm, GUD_REQ_SET_STATE_COMMIT, 0, NULL, 0); - - if (crtc->state->active_changed) - gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, crtc->state->active); - - if (!fb) - goto ctrl_disable; - ret =3D drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE); if (ret) - goto ctrl_disable; + goto out; =20 drm_atomic_helper_damage_iter_init(&iter, old_state, new_state); drm_atomic_for_each_plane_damage(&iter, &damage) @@ -632,9 +658,6 @@ void gud_plane_atomic_update(struct drm_plane *plane, =20 drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE); =20 -ctrl_disable: - if (!crtc->state->enable) - gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0); - +out: drm_dev_exit(idx); } --=20 2.52.0