linux-kernel - Re: [PATCH v4] drm/vblank: Increase timeout in drm_wait_one

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Message-ID: <f19d9468-a974-4b49-bb5a-c0900f6a705e@suse.de>
Date: Thu, 4 Dec 2025 08:34:43 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Chintan Patel <chintanlike@...il.com>, maarten.lankhorst@...ux.intel.com,
 maxime.ripard@...nel.org, airlied@...il.com, simona@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 syzbot+147ba789658184f0ce04@...kaller.appspotmail.com
Subject: Re: [PATCH v4] drm/vblank: Increase timeout in drm_wait_one_vblank()

Hi

Am 04.12.25 um 04:44 schrieb Chintan Patel:
> Hi Thomas,
>
> On 10/28/25 10:14, Thomas Zimmermann wrote:
>>
>>
>> Am 28.10.25 um 04:43 schrieb Chintan Patel:
>>> Currently, wait_event_timeout() in drm_wait_one_vblank() uses a 100ms
>>> timeout. Under heavy scheduling pressure or rare delayed vblank
>>> handling, this can trigger WARNs unnecessarily.
>>>
>>> Increase the timeout to 1000ms to reduce spurious WARNs, while still
>>> catching genuine issues.
>>
>> Thanks a lot.
>>
>>>
>>> Reported-by: syzbot+147ba789658184f0ce04@...kaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=147ba789658184f0ce04
>>> Tested-by: syzbot+147ba789658184f0ce04@...kaller.appspotmail.com
>>> Signed-off-by: Chintan Patel <chintanlike@...il.com>
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>
> Gentle ping on this patch. Please let me know if there are any issues 
> with the patch, or if it requires any changes or further testing.

It's on its way already. This patch has been merged as commit 
f050da08a4ed ("drm/vblank: Increase timeout in drm_wait_one_vblank()"). 
It was part of the recent PR for v6.19-rc1.

Best regards
Thomas

[1] 
https://lore.kernel.org/dri-devel/CAPM=9tySHmq2KLAvW95MeKcb-37gZBhHTY5hf4dCTgUFLd+RKg@mail.gmail.com/T/#u

>
>>>
>>> v2:
>>>   - Dropped unnecessary in-code comment (suggested by Thomas 
>>> Zimmermann)
>>>   - Removed else branch, only log timeout case
>>>
>>> v3:
>>>   - Replaced drm_dbg_kms()/manual logging with drm_err() (suggested 
>>> by Ville Syrjälä)
>>>   - Removed unnecessary curr = drm_vblank_count() (suggested by 
>>> Thomas Zimmermann)
>>>   - Fixed commit message wording ("invalid userspace calls" → 
>>> "delayed vblank handling")
>>>
>>> v4:
>>>   - Keep the original drm_WARN() to catch genuine kernel issues
>>>   - Increased timeout from 100ms → 1000ms to reduce spurious WARNs 
>>> (suggested by Thomas Zimmermann)
>>> ---
>>>   drivers/gpu/drm/drm_vblank.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_vblank.c 
>>> b/drivers/gpu/drm/drm_vblank.c
>>> index 46f59883183d..f779103b261b 100644
>>> --- a/drivers/gpu/drm/drm_vblank.c
>>> +++ b/drivers/gpu/drm/drm_vblank.c
>>> @@ -1303,7 +1303,7 @@ void drm_wait_one_vblank(struct drm_device 
>>> *dev, unsigned int pipe)
>>>       ret = wait_event_timeout(vblank->queue,
>>>                    last != drm_vblank_count(dev, pipe),
>>> -                 msecs_to_jiffies(100));
>>> +                 msecs_to_jiffies(1000));
>>>       drm_WARN(dev, ret == 0, "vblank wait timed out on crtc %i\n", 
>>> pipe);
>>
>

-- 
--
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)