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Fri, 4 Sep 2026 06:19:17 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id v+MVDOVimmrERwAAD6G6ig (envelope-from ); Fri, 04 Sep 2026 06:19:17 +0000 Message-ID: Date: Fri, 4 Sep 2026 08:19:16 +0200 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] drm/vblank: Don't arm vblank timer with invalid frame duration To: Thorsten Leemhuis , Roman Ilin Cc: David Airlie , Simona Vetter , Maxime Ripard , Louis Chauvet , Javier Martinez Canillas , Dmitry Osipenko , dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , Peter Arnesen , Linux kernel regressions list , Maarten Lankhorst References: <20260613224434.96501-1-me@romanilin.is> <20260702181027.98526-1-me@romanilin.is> <3b192119-9709-4f21-841f-a4706cc85e4a@suse.de> <0600a3f0-b2d2-4a07-ab21-f590c2979612@leemhuis.info> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <0600a3f0-b2d2-4a07-ab21-f590c2979612@leemhuis.info> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Level: X-Spam-Score: -2.80 X-Spam-Flag: NO X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; TAGGED_RCPT(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[15]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[gmail.com,ffwll.ch,kernel.org,bootlin.com,redhat.com,collabora.com,lists.freedesktop.org,lists.linux.dev,vger.kernel.org,linux.intel.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid,suse.com:url,imap1.dmz-prg2.suse.org:helo] Hi Thorsten Am 03.09.26 um 16:07 schrieb Thorsten Leemhuis: > On 7/3/26 09:26, Thomas Zimmermann wrote: >> Am 02.07.26 um 20:23 schrieb Roman Ilin: >>> Apologies, I accidentally fired off send-email before saving my final >>> changelog notes. Please ignore the changelog and notes in the original >>> v3 email. >>> >>> The actual changes in v3 are: >>> >>> - Changed the WARN_ON_ONCE to drm_dbg_kms (to avoid user-triggerable >>>    panics). >> We want to know when this happens. And user space will only be able to >> trigger this once, so there's no risk of spamming the kernel log. > Hmmm, just wondering: what's the status here? > > Roman Ilin, did you loose interest? Or was this continued somewhere or > maybe even resolved and I just missed that? > > Thomas: if Roman left this behind, could you maybe handle this, as it > fixes a regressions that iirc is caused by a change of yours? Or is it > fine for some reason to ignore this, even if the userland problem that > triggers this is still unfixed afaics? Side note: I by chance saw that > the latter a few days ago got a new comment from someone that ran into it. > https://gitlab.freedesktop.org/spice/linux/vd_agent/-/work_items/52 AFAICT it was almost there except for the error messaging. The v4 then never happened. I can finish the patch if Roman is no longer around. Best regards Thomas > > Ciao, Thorsten >> So this is not really a problem. drm_WARN_ON_ONCE was ok for that. You >> can also use a regular DRM print macro. But instead of drm_dbg_kms() >> should use drm_err_once(). But please also output linedur_ns and >> framedur_ns in the error. We want to know which of them is incorrect. >> You can also add more information to the error message. See [1] for the >> mode-formating macros. >> >> [1] https://elixir.bootlin.com/linux/v7.1.2/source/include/drm/ >> drm_modes.h#L422 >> >> >>> - Updated drm_calc_timestamping_constants with the goto error fallback >>>    to clear the stale state. >>> >>> Also, an automated review bot pointed out an AB-BA deadlock in >>> drm_crtc_vblank_start_timer(). But I am leaving this out of the patch to >>> keep the fixes orthogonal. >>> >>> Sorry for the noise. >>> >>>> On Jul 2, 2026, at 21:10, 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. >>>> >>>> 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"). >>>> >>>> To fix this, modify drm_calc_timestamping_constants() to use u64 for >>>> calculations, check for INT_MAX overflows, and return an error code. >>>> drm_crtc_vblank_start_timer() will then propagate the error, enabling >>>> the driver to fall back to immediate vblank events. Valid modes are >>>> unaffected, and the timer self-heals on the next mode with a sane clock. >>>> >>>> Fixes: 74afeb812850 ("drm/vblank: Add vblank timer") >>>> Suggested-by: Thomas Zimmermann >>>> Signed-off-by: Roman Ilin >>>> --- >>>> Changes in v3: >>>> >>>> - Changed the WARN_ON_ONCE to drm_err_once >>>> >>>> Notes: >>>> >>>> >>>> >>>> drivers/gpu/drm/drm_vblank.c | 71 +++++++++++++++++++++++------------- >>>> include/drm/drm_vblank.h     |  4 +- >>>> 2 files changed, 48 insertions(+), 27 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c >>>> index f90fb2d13..629b9fcc7 100644 >>>> --- a/drivers/gpu/drm/drm_vblank.c >>>> +++ b/drivers/gpu/drm/drm_vblank.c >>>> @@ -631,42 +631,51 @@ EXPORT_SYMBOL(drm_crtc_vblank_waitqueue); >>>>   * drm_crtc_vblank_helper_get_vblank_timestamp(). They are derived from >>>>   * CRTC's true scanout timing, so they take things like panel >>>> scaling or >>>>   * other adjustments into account. >>>> + * >>>> + * Returns: >>>> + * 0 on success, or a negative errno code otherwise. >>>>   */ >>>> -void drm_calc_timestamping_constants(struct drm_crtc *crtc, >>>> -     const struct drm_display_mode *mode) >>>> +int drm_calc_timestamping_constants(struct drm_crtc *crtc, >>>> +    const struct drm_display_mode *mode) >>>> { >>>> struct drm_device *dev = crtc->dev; >>>> unsigned int pipe = drm_crtc_index(crtc); >>>> struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc); >>>> - int linedur_ns = 0, framedur_ns = 0; >>>> + u64 linedur_ns, framedur_ns; >>>> int dotclock = mode->crtc_clock; >>>> + unsigned int frame_size; >>>> >>>> if (!drm_dev_has_vblank(dev)) >>>> - return; >>>> + return 0; >>>> >>>> if (drm_WARN_ON(dev, pipe >= dev->num_crtcs)) >>>> - return; >>>> + return -EINVAL; >>>> >>>> - /* Valid dotclock? */ >>>> - if (dotclock > 0) { >>>> - int frame_size = mode->crtc_htotal * mode->crtc_vtotal; >>>> + if (dotclock <= 0) { >>>> + drm_err(dev, "crtc %u: Can't calculate constants, dotclock = %d!\n", >> Please turn this into drm_err_once() because this call can actually be >> triggered repeatedly from userspace. >> >> Best regards >> Thomas >> >> >>>> + crtc->base.id, dotclock); >>>> + goto error; >>>> + } >>>> >>>> - /* >>>> - * Convert scanline length in pixels and video >>>> - * dot clock to line duration and frame duration >>>> - * in nanoseconds: >>>> - */ >>>> - linedur_ns  = div_u64((u64) mode->crtc_htotal * 1000000, dotclock); >>>> - framedur_ns = div_u64((u64) frame_size * 1000000, dotclock); >>>> + frame_size = (unsigned int)mode->crtc_htotal * (unsigned int)mode- >>>>> crtc_vtotal; >>>> - /* >>>> - * Fields of interlaced scanout modes are only half a frame duration. >>>> - */ >>>> - if (mode->flags & DRM_MODE_FLAG_INTERLACE) >>>> - framedur_ns /= 2; >>>> - } else { >>>> - drm_err(dev, "crtc %u: Can't calculate constants, dotclock = 0!\n", >>>> - crtc->base.id); >>>> + /* >>>> + * Convert scanline length in pixels and video dot clock to line >>>> duration >>>> + * and frame duration in nanoseconds. >>>> + */ >>>> + linedur_ns  = div_u64((u64)mode->crtc_htotal * 1000000, dotclock); >>>> + framedur_ns = div_u64((u64)frame_size * 1000000, dotclock); >>>> + >>>> + /* >>>> + * Fields of interlaced scanout modes are only half a frame duration. >>>> + */ >>>> + if (mode->flags & DRM_MODE_FLAG_INTERLACE) >>>> + framedur_ns /= 2; >>>> + >>>> + if (linedur_ns > INT_MAX || framedur_ns > INT_MAX) { >>>> + drm_dbg_kms(dev, "crtc %u: Can't calculate constants, mode clock >>>> too small!\n", >>>> +    crtc->base.id); >>>> + goto error; >>>> } >>>> >>>> vblank->linedur_ns  = linedur_ns; >>>> @@ -678,7 +687,16 @@ void drm_calc_timestamping_constants(struct >>>> drm_crtc *crtc, >>>>      crtc->base.id, mode->crtc_htotal, >>>>      mode->crtc_vtotal, mode->crtc_vdisplay); >>>> drm_dbg_core(dev, "crtc %u: clock %d kHz framedur %d linedur %d\n", >>>> -     crtc->base.id, dotclock, framedur_ns, linedur_ns); >>>> +     crtc->base.id, dotclock, >>>> +     vblank->framedur_ns, vblank->linedur_ns); >>>> + >>>> + return 0; >>>> + >>>> +error: >>>> + vblank->linedur_ns  = 0; >>>> + vblank->framedur_ns = 0; >>>> + drm_mode_copy(&vblank->hwmode, mode); >>>> + return -EINVAL; >>>> } >>>> EXPORT_SYMBOL(drm_calc_timestamping_constants); >>>> >>>> @@ -2221,6 +2239,7 @@ int drm_crtc_vblank_start_timer(struct drm_crtc >>>> *crtc) >>>> struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc); >>>> struct drm_vblank_crtc_timer *vtimer = &vblank->vblank_timer; >>>> unsigned long flags; >>>> + int ret; >>>> >>>> if (!vtimer->crtc) { >>>> /* >>>> @@ -2239,7 +2258,9 @@ int drm_crtc_vblank_start_timer(struct drm_crtc >>>> *crtc) >>>> hrtimer_try_to_cancel(&vtimer->timer); >>>> } >>>> >>>> - drm_calc_timestamping_constants(crtc, &crtc->mode); >>>> + ret = drm_calc_timestamping_constants(crtc, &crtc->mode); >>>> + if (ret) >>>> + return ret; >>>> >>>> spin_lock_irqsave(&vtimer->interval_lock, flags); >>>> vtimer->interval = ns_to_ktime(vblank->framedur_ns); >>>> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h >>>> index 2fcef9c0f..d99772dfa 100644 >>>> --- a/include/drm/drm_vblank.h >>>> +++ b/include/drm/drm_vblank.h >>>> @@ -311,8 +311,8 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc); >>>> u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc); >>>> void drm_crtc_vblank_restore(struct drm_crtc *crtc); >>>> >>>> -void drm_calc_timestamping_constants(struct drm_crtc *crtc, >>>> -     const struct drm_display_mode *mode); >>>> +int drm_calc_timestamping_constants(struct drm_crtc *crtc, >>>> +    const struct drm_display_mode *mode); >>>> wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc); >>>> void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc, >>>>    u32 max_vblank_count); >>>> -- >>>> 2.54.0 >>>> -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)