Re: [Intel-gfx] [PATCH] drm/i915/guc: Use correct context lock when callig clr_context_registered

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 09/12/2021 19:14, Daniele Ceraolo Spurio wrote:
> 
> 
> On 12/9/2021 10:48 AM, Matthew Brost wrote:
>> s/ce/cn/ when grabbing guc_state.lock before calling
>> clr_context_registered.
>>
>> Fixes: 0f7976506de61 ("drm/i915/guc: Rework and simplify locking")
>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>> Cc: <stable@vger.kernel.org>

I think Cc: stable is not needed here:

$ git tag --contains 0f7976506de61
drm-intel-fixes-2021-11-18
drm-intel-gt-next-2021-10-08
drm-intel-gt-next-2021-10-21
drm-intel-gt-next-2021-11-22
drm-intel-next-2021-10-15
drm-intel-next-fixes-2021-11-09
v5.16-rc1
v5.16-rc2
v5.16-rc3
v5.16-rc4

So still can hit 5.16 via fixes. Rodrigo, did I get this right and you 
will be able to pick it up next week or so?

> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> 
> I'm assuming we didn't see any splat from the lockdep assert in 
> clr_context_registered in our CI runs because we never hit this case as 
> it requires 64k+ contexts. Maybe we can add a selftest to purposely 
> exercise this path? Not a blocker for merging this fix.

Was the bug found by inspection or reported?

Given the buggy function is called steal_guc_id, so if the implication 
is there is no testing for guc id stealing, then it indeed please add 
some coverage ASAP.

Regards,

Tvrtko

> 
> Daniele
> 
>> ---
>>   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ++--
>>   1 file changed, 2 insertions(+), 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 1f9d4fde421f..9b7b4f4e0d91 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>> @@ -1937,9 +1937,9 @@ static int steal_guc_id(struct intel_guc *guc, 
>> struct intel_context *ce)
>>           list_del_init(&cn->guc_id.link);
>>           ce->guc_id = cn->guc_id;
>> -        spin_lock(&ce->guc_state.lock);
>> +        spin_lock(&cn->guc_state.lock);
>>           clr_context_registered(cn);
>> -        spin_unlock(&ce->guc_state.lock);
>> +        spin_unlock(&cn->guc_state.lock);
>>           set_context_guc_id_invalid(cn);
>