Re: [PATCH] drm/i915/guc: Remove racey GEM_BUG_ON

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

On 12/9/2021 11:57 AM, Matthew Brost wrote:
> On Thu, Dec 09, 2021 at 11:26:09AM -0800, Daniele Ceraolo Spurio wrote:
>>
>> On 12/9/2021 10:51 AM, Matthew Brost wrote:
>>> A full GT can race with the last context put resulting in the context

forgot to mention earlier but you're missing "reset" here

>>> ref count being zero but the destroyed bit not yet being set. Remove
>>> GEM_BUG_ON in scrub_guc_desc_for_outstanding_g2h that asserts the
>>> destroyed bit must be set in ref count is zero.
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 2 --
>>>    1 file changed, 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> index 9b7b4f4e0d91..0f99bb83293a 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -1040,8 +1040,6 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
>>>    		spin_unlock(&ce->guc_state.lock);
>>> -		GEM_BUG_ON(!do_put && !destroyed);
>>> -
>> Do we need to re-queue/flush the destroyer work to make sure it runs before
>> we reset, or is it ok for that to run in parallel?
>>
> The code in the put path will either see the reset or that it isn't
> registered and destroy the context without any interaction with the GuC.

ok.

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

Daniele

>
> Matt
>
>> Daniele
>>
>>>    		if (pending_enable || destroyed || deregister) {
>>>    			decr_outstanding_submission_g2h(guc);
>>>    			if (deregister)