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

[Matthew Auld <matthew.auld@intel.com>]

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. 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;
-

?

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