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bh=mbGa7/pJLqNh9s5lB1eARfC8HZvlkVr7AS4gBr7kAhI=; b=sDIkijTXOHEuKluliVY5fBgXxuB1WncaOrvU0jFMAjrrRt9oL1i9kCnpvxx8x6YZhUVriY fvziUnSPvecZKvDQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 821931321C; Wed, 28 Oct 2026 07:27:35 +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 0//wCeej4Wp8PwAAD6G6ig (envelope-from ); Wed, 28 Oct 2026 07:27:35 +0000 Message-ID: <2b2f1c04-4638-4622-9816-639d4fffa51d@suse.de> Date: Wed, 28 Oct 2026 08:27:34 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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> <7f21f160-f637-4b63-aa15-066d7b18e2ed@leemhuis.info> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[bootlin.com:url,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,suse.de:email,suse.com:url] X-Spam-Score: -12.00 Hi Am 27.10.26 um 08:49 schrieb Thorsten Leemhuis: > On 9/14/26 13:00, Thomas Zimmermann wrote: >> Am 11.09.26 um 09:39 schrieb Thorsten Leemhuis: >>> On 9/4/26 08:19, Thomas Zimmermann wrote: >>>> 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. >>>>>> 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, [...] >>>> 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. >>> No answer from Roman since then, so yes, that would be great! Tia! >> I've now sent out an update with minor changes. > Many thx again. But the thing is: it still sits on the list waiting for > review afaics: > > https://lore.kernel.org/all/20260914110004.211027-1-tzimmermann@suse.de/ > > Can you maybe prod the right people to finally get this resolved? Or > what should be do instead? The right people are in cc already. It's just that no one reviewed. I'll ping them to get this resolved. 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: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)