Hi,
please also see this bug report:
https://gitlab.freedesktop.org/spice/linux/vd_agent/-/work_items/52
Am 30.06.26 um 14:06 schrieb Thorsten Leemhuis:
On 6/14/26 00:44, Roman Ilin wrote:
When a CRTC's display mode carries a too small pixel clock,
drm_calc_timestamping_constants() computes a frame duration that
exceeds INT_MAX. drm_vblank_crtc.framedur_ns becomes negative.
drm_crtc_vblank_start_timer() then arms the vblank hrtimer with this
interval, after which vblank events are no longer delivered. Pending
page flips never complete and the display appears frozen.
Roman, what's the status here? Does the problem still happen with
7.2-rc1? Sounds like it likely will, just want to make sure before
prodding Thomas about it, who authored and committed the change that
causes this regression.
Side note: CCing Peter Arnesen, who seems to be affected as well.
Quoting a message that was CCed to the regression list, but apparently
was rejected there:
"""
Hi everyone,
I am experiencing a similar Wayland display freeze on Kernel 7.0
described in Roman Ilin's recent patch thread ("drm/vblank: Don't arm
vblank timer with invalid frame duration").
Since my laptop consistently reproduces this freeze on boot, I am
reaching out to offer my hardware for testing if you need verification
that this patch resolves the issue on the newer Ryzen AI architectures.
My System:
* CPU / iGPU: AMD Ryzen AI 9 HX
* dGPU: NVIDIA GeForce RTX 5070
* OS: Fedora 44, Kubuntu 26.04 and Nobara Linux (Fedora-based) / Wayland
* Regression Status: Works perfectly on Kernel 6.19. Fails on Kernel 7.0.
* Tested Workarounds: Kernel parameters amdgpu.dcdebugmask=0x10, 0x410,
and amdgpu.sg_display=0 do not bypass the freeze.
Please let me know if you need me to pull specific dmesg logs or similar
from the frozen state, or if there is a specific patched branch you
would like me to compile and boot to verify the fix.
Regards
Peter
"""
Peter, would be great if you could test 7.2-rc1, too. And if you really
think the problem is the same, it might be worth trying Roman's patch.
Ciao, Thorsten
This could be triggered on virtio-gpu guests that have dynamic resolution
enabled: when the SPICE agent or the X server resizes the output, it
submits a mode whose pixel clock is off by a factor of 1000, e.g.:
clock = 406 kHz, htotal = 3152, vtotal = 2148
framedur_ns = 3152 * 2148 * 1000000 / 406 = 16675852216 ns (~16.7 s)
16675852216 does not fit into an int and wraps to roughly -504000000.
ns_to_ktime() then yields a negative interval and the timer stops working.
Found by bisection, which pointed at commit a036f5fceedb ("drm/virtgpu:
Use vblank timer"). That commit merely made virtio-gpu use the vblank
timer and thereby exposed the pre-existing problem in the timer setup
added by commit 74afeb812850 ("drm/vblank: Add vblank timer").
Reject a non-positive frame duration in drm_crtc_vblank_start_timer() and
return an error. enable_vblank then fails and the driver falls back to
sending the vblank event immediately, as it did before the vblank timer
was introduced. Valid modes are unaffected, and the timer self-heals on
the next mode that has a sane clock.
Fixes: 74afeb812850 ("drm/vblank: Add vblank timer")
Cc: [email protected]
Signed-off-by: Roman Ilin <[email protected]>
---
Notes:
Based on v7.1-rc7. Tested on 6.19 and 7.1-rc7.
Open questions:
This relies on the int overflow producing a negative value. The deeper
issue is that drm_calc_timestamping_constants() truncates framedur_ns to
int. Would you prefer to widen framedur_ns to s64, or to bound the
interval here (e.g. reject framedur_ns above one second) so that any
bogus interval is rejected regardless of sign?
Should virtio-gpu additionally sanitize the user-supplied clock in its
atomic_check (similar to vmwgfx for the clock==0 case) so the
vblank-timer throttling is preserved for these resizes, instead of
falling back to immediate events?
drivers/gpu/drm/drm_vblank.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index f78bf37f1..557cd0bc8 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -2235,7 +2235,13 @@ int drm_crtc_vblank_start_timer(struct drm_crtc *crtc)
drm_calc_timestamping_constants(crtc, &crtc->mode);
+ /*
+ * Return an error so the driver falls back to sending vblank events
+ * when a small mode clock yields a frame duration exceeding INT_MAX.
+ */
+ if (vblank->framedur_ns <= 0)
+ return -EINVAL;
+
spin_lock_irqsave(&vtimer->interval_lock, flags);
vtimer->interval = ns_to_ktime(vblank->framedur_ns);
spin_unlock_irqrestore(&vtimer->interval_lock, flags);
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
