Re: [PATCH] drm/xe/ufence: ufence can be signaled right after wait_woken

[Nirmoy Das <nirmoy.das@intel.com>]

On 10/11/2024 5:16 PM, Matthew Auld wrote:
> On 11/10/2024 15:10, Nirmoy Das wrote:
>>
>> On 10/11/2024 3:25 PM, Nirmoy Das wrote:
>>> do_comapre() can return success after wait_woken() which is treated as
>>> -ETIME here.
>>
>> s/after wait_woken()/after timedout wait_woken()
>>
>> I will resend with that change.
>>
>>>
>>> Fixes: e670f0b4ef24 ("drm/xe/uapi: Return correct error code for xe_wait_user_fence_ioctl")
>>> Cc: <stable@vger.kernel.org> # v6.8+
>>> Cc: Bommu Krishnaiah <krishnaiah.bommu@intel.com>
>>> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1630
>>> Cc: Matthew Auld <matthew.auld@intel.com>
>>> Cc: Matthew Brost <matthew.brost@intel.com>
>>> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
>>> ---
>>>   drivers/gpu/drm/xe/xe_wait_user_fence.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_wait_user_fence.c b/drivers/gpu/drm/xe/xe_wait_user_fence.c
>>> index d46fa8374980..d532283d4aa3 100644
>>> --- a/drivers/gpu/drm/xe/xe_wait_user_fence.c
>>> +++ b/drivers/gpu/drm/xe/xe_wait_user_fence.c
>>> @@ -169,7 +169,7 @@ int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
>>>               args->timeout = 0;
>>>       }
>>>   -    if (!timeout && !(err < 0))
>
> Since err > 0 is impossible, this could be written as: && err == 0.
>
> So I think this is saying: if we have timedout and err does not already have an error set then go ahead and set to -ETIME since we hit the timeout.

This is the issue here. This assumption is wrong that if timeout happen then return -ETIME even though the fence is signaled.


> But it might have -EIO or -ERESTARTSYS for example, which should then take precedence over -ETIME...
>
>>> +    if (!timeout && err < 0)
>
> ...this would then trample the existing err. The err can either be zero or an existing error at this point, so I think just remove this entire check:
>
> -       if (!timeout && !(err < 0))
> -               err = -ETIME;
> -
>
> ?


Yes, this works for me. The for loops sets err correctly even when there is real timeout on not-signaled fence.

I will resend a v2.


Regards,

Nirmoy

>
>>>           err = -ETIME;
>>>         if (q)