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drm/gud: fix NULL crtc dereference on display disable

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gud_plane_atomic_update() currently handles both crtc state and
framebuffer updates - the complexity has led to a few accidental
NULL pointer dereferences.

Commit dc2d5ddb19 ("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.vanilla.gud.fc42.x86_64 #1 PREEMPT(lazy)
RIP: 0010:gud_plane_atomic_update+0x148/0x470 [gud]
 <TASK>
 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

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202601142159.0v8ilfVs-lkp@intel.com/
Fixes: 73cfd166e0 ("drm/gud: Replace simple display pipe with DRM atomic helpers")
Cc: <stable@vger.kernel.org> # 6.19.x
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Shenghao Yang <me@shenghaoyang.info>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Ruben Wauters <rubenru09@aol.com>
Signed-off-by: Ruben Wauters <rubenru09@aol.com>
Link: https://patch.msgid.link/20260222054551.80864-1-me@shenghaoyang.info
This commit is contained in:
Shenghao Yang 2026-02-22 13:45:51 +08:00 committed by Ruben Wauters
parent 46d8a07b4a
commit 7149be786d
No known key found for this signature in database
GPG Key ID: D27E50C050AE0CE1
3 changed files with 48 additions and 19 deletions
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9
drivers/gpu/drm/gud/gud_drv.c
View File

@ -339,7 +339,9 @@ static int gud_stats_debugfs(struct seq_file *m, void *data)
}
static const struct drm_crtc_helper_funcs gud_crtc_helper_funcs = {
.atomic_check = drm_crtc_helper_atomic_check
.atomic_check = drm_crtc_helper_atomic_check,
.atomic_enable = gud_crtc_atomic_enable,
.atomic_disable = gud_crtc_atomic_disable,
};
static const struct drm_crtc_funcs gud_crtc_funcs = {
@ -364,6 +366,10 @@ static const struct drm_plane_funcs gud_plane_funcs = {
DRM_GEM_SHADOW_PLANE_FUNCS,
};
static const struct drm_mode_config_helper_funcs gud_mode_config_helpers = {
.atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
};
static const struct drm_mode_config_funcs gud_mode_config_funcs = {
.fb_create = drm_gem_fb_create_with_dirty,
.atomic_check = 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 = le32_to_cpu(desc.min_height);
drm->mode_config.max_height = le32_to_cpu(desc.max_height);
drm->mode_config.funcs = &gud_mode_config_funcs;
drm->mode_config.helper_private = &gud_mode_config_helpers;
/* Format init */
formats_dev = devm_kmalloc(dev, GUD_FORMATS_MAX_NUM, GFP_KERNEL);

4
drivers/gpu/drm/gud/gud_internal.h
View File

@ -62,6 +62,10 @@ int gud_usb_set_u8(struct gud_device *gdrm, u8 request, u8 val);
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,

54
drivers/gpu/drm/gud/gud_pipe.c
View File

@ -580,6 +580,39 @@ int gud_plane_atomic_check(struct drm_plane *plane,
return ret;
}
void gud_crtc_atomic_enable(struct drm_crtc *crtc,
struct drm_atomic_state *state)
{
struct drm_device *drm = crtc->dev;
struct gud_device *gdrm = to_gud_device(drm);
int idx;
if (!drm_dev_enter(drm, &idx))
return;
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, 1);
drm_dev_exit(idx);
}
void gud_crtc_atomic_disable(struct drm_crtc *crtc,
struct drm_atomic_state *state)
{
struct drm_device *drm = crtc->dev;
struct gud_device *gdrm = to_gud_device(drm);
int idx;
if (!drm_dev_enter(drm, &idx))
return;
gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, 0);
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 +640,12 @@ void gud_plane_atomic_update(struct drm_plane *plane,
mutex_unlock(&gdrm->damage_lock);
}
if (!drm_dev_enter(drm, &idx))
if (!crtc || !drm_dev_enter(drm, &idx))
return;
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 = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
if (ret)
goto ctrl_disable;
goto out;
drm_atomic_helper_damage_iter_init(&iter, old_state, new_state);
drm_atomic_for_each_plane_damage(&iter, &damage)
@ -632,9 +653,6 @@ void gud_plane_atomic_update(struct drm_plane *plane,
drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
ctrl_disable:
if (!crtc->state->enable)
gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);
out:
drm_dev_exit(idx);
}