Re: [PATCH 1/2] drm//amdgpu: Always sync fence before unlock eviction_lock

["Christian König" <christian.koenig@amd.com>]

Am 13.03.20 um 10:29 schrieb Pan, Xinhui:
>
>> 2020年3月13日 16:52，Koenig, Christian <Christian.Koenig@amd.com> 写道：
>>
>> Am 13.03.20 um 08:43 schrieb xinhui pan:
>>> The fence generated in ->commit is a shared one, so add it to resv.
>>> And we need do that with eviction lock hold.
>>>
>>> Currently we only sync last_direct/last_delayed before ->prepare. But we
>>> fail to sync the last fence generated by ->commit. That cuases problems
>>> if eviction happenes later, but it does not sync the last fence.
>> NAK, that won't work.
>>
>> We can only add fences when the dma_resv object is locked and that is only the case when validating.
>>
> well, tha tis true.
> but considering this is a PT BO, and only eviction has race on it AFAIK.
> as for the individualized resv in bo release, we unref PT BO just after that.
> I am still thinking of other races in the real world.

We should probably just add all pipelined/delayed submissions directly 
to the reservation object in amdgpu_vm_sdma_commit().

Only the direct and invalidating submissions can't be added because we 
can't grab the reservation object in the MMU notifier.

Can you prepare a patch for this?

Regards,
Christian.

>
> thanks
> xinhui
>
>> I'm considering to just partially revert the patch originally stopping to add fences and instead only not add them when invalidating in a direct submit.
>>
>> Christian.
>>
>>> Cc: Christian König <christian.koenig@amd.com>
>>> Cc: Alex Deucher <alexander.deucher@amd.com>
>>> Cc: Felix Kuehling <Felix.Kuehling@amd.com>
>>> Signed-off-by: xinhui pan <xinhui.pan@amd.com>
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 9 +++++++--
>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> index 73398831196f..f424b5969930 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> @@ -1582,6 +1582,7 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
>>>   	struct amdgpu_vm_update_params params;
>>>   	enum amdgpu_sync_mode sync_mode;
>>>   	int r;
>>> +	struct amdgpu_bo *root = vm->root.base.bo;
>>>     	memset(&params, 0, sizeof(params));
>>>   	params.adev = adev;
>>> @@ -1604,8 +1605,6 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
>>>   	}
>>>     	if (flags & AMDGPU_PTE_VALID) {
>>> -		struct amdgpu_bo *root = vm->root.base.bo;
>>> -
>>>   		if (!dma_fence_is_signaled(vm->last_direct))
>>>   			amdgpu_bo_fence(root, vm->last_direct, true);
>>>   @@ -1623,6 +1622,12 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
>>>     	r = vm->update_funcs->commit(&params, fence);
>>>   +	if (!dma_fence_is_signaled(vm->last_direct))
>>> +		amdgpu_bo_fence(root, vm->last_direct, true);
>>> +
>>> +	if (!dma_fence_is_signaled(vm->last_delayed))
>>> +		amdgpu_bo_fence(root, vm->last_delayed, true);
>>> +
>>>   error_unlock:
>>>   	amdgpu_vm_eviction_unlock(vm);
>>>   	return r;

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