[PATCH v2 2/2] drm/i915: Never return 0 if not all requests retired

[Andrzej Hajda]

On 21.11.2022 09:30, Janusz Krzysztofik wrote:
> Hi Nimroy,
>
> Thanks for looking at this.
>
> On Friday, 18 November 2022 20:56:50 CET Das, Nirmoy wrote:
>> On 11/18/2022 11:42 AM, Janusz Krzysztofik wrote:
>>> Users of intel_gt_retire_requests_timeout() expect 0 return value on
>>> success.  However, we have no protection from passing back 0 potentially
>>> returned by a call to dma_fence_wait_timeout() when it succedes right
>>> after its timeout has expired.
>>>
>>> Replace 0 with -ETIME before potentially using the timeout value as return
>>> code, so -ETIME is returned if there are still some requests not retired
>>> after timeout, 0 otherwise.
>>>
>>> v2: Move the added lines down so flush_submission() is not affected.
>>>
>>> Fixes: f33a8a51602c ("drm/i915: Merge wait_for_timelines with
> retire_request")
>>> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
>>> Cc: stable at vger.kernel.org # v5.5+
>>> ---
>>>    drivers/gpu/drm/i915/gt/intel_gt_requests.c | 3 +++
>>>    1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/
> drm/i915/gt/intel_gt_requests.c
>>> index edb881d756309..3ac4603eeb4ee 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>>> @@ -199,6 +199,9 @@ out_active:	spin_lock(&timelines->lock);
>>>    	if (remaining_timeout)
>>>    		*remaining_timeout = timeout;
>>>    
>>> +	if (!timeout)
>>> +		timeout = -ETIME;
>> This will return error, -ETIME when 0 timeout is passed,
>> intel_gt_retire_requests().
> Yes, but only when active_count is not 0 after we loop through
> timelines->active_list calling retire_requests() on each and counting up
> failures in active_count.

Moving this line just after the call to dma_fence_wait_timeout should 
solve the controversy.

Regards
Andrzej

>
>> We don't want that.
> When 0 timeout is passed to intel_gt_retire_requests(), do we really want it
> to return 0 unconditionally, or are we rather interested if those calls to
> retire_requests() succeeded?
>
>> I think you can use a separate variable to store
>> return val from the dma_fence_wait_timeout()
>>
>>
>> Regards,
>>
>> Nirmoy
>>
>>> +
>>>    	return active_count ? timeout : 0;
> If active count is 0, we return 0 regardless of timeout value, and that's OK.
> However, if active_count is not 0, we shouldn't return 0, I believe, we should
> return either remaining time if some left, or error (-ETIME) if not.  If you
> think I'm wrong, please explain why.
>
> Thanks,
> Janusz
>
>>>    }
>>>    
>
>
>