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

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Message-ID: <67663eda-dce6-48e7-ad54-572bbce8b944@gmail.com>
Date: Wed, 3 Dec 2025 19:44:49 -0800
From: Chintan Patel <chintanlike@...il.com>
To: Thomas Zimmermann <tzimmermann@...e.de>,
 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 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.

>>
>> 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);
>