Re: [Intel-gfx] [PATCH] drm/i915: fix remaining_timeout in intel_gt_retire_requests_timeout

["Ceraolo Spurio, Daniele" <daniele.ceraolospurio@intel.com>]

On 3/25/2022 11:37 AM, Das, Nirmoy wrote:
>
> On 3/25/2022 6:58 PM, Daniele Ceraolo Spurio wrote:
>> In intel_gt_wait_for_idle, we use the remaining timeout returned from
>> intel_gt_retire_requests_timeout to wait on the GuC being idle. However,
>> the returned variable can have a negative value if something goes wrong
>> during the wait, leading to us hitting a GEM_BUG_ON in the GuC wait
>> function.
>> To fix this, make sure to only return the timeout if it is positive.
>>
>> Fixes: b97060a99b01b ("drm/i915/guc: Update intel_gt_wait_for_idle to 
>> work with GuC")
>> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: John Harrison <john.c.harrison@intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_gt_requests.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c 
>> b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>> index edb881d756309..ef70c209976d8 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>> @@ -197,7 +197,7 @@ out_active: spin_lock(&timelines->lock);
>>           active_count++;
>>         if (remaining_timeout)
>> -        *remaining_timeout = timeout;
>> +        *remaining_timeout = timeout > 0 ? timeout : 0;
>
>
> Should the last flush_submission() be  "if ( timeout > 0 
> &&flush_submission(gt, timeout))" ?

I considered it, but flush_submission only checks for timeout != 0 so it 
won't accidentally make use of a negative value thinking it's positive. 
I don't know if the flush is purposely done even if timeout is negative 
or if that's a mistake, but that code has been there long before we 
modified the function to return the remaining timeout and never seems to 
have caused issues, so I decided not to change it.

Daniele

>
>
> Nirmoy
>
>>         return active_count ? timeout : 0;
>>   }