[PATCH] drm/kfd: fix ttm_bo_release warning

[Yu, Lang]

[AMD Official Use Only]



>-----Original Message-----
>From: Koenig, Christian <Christian.Koenig at amd.com>
>Sent: Thursday, September 23, 2021 10:52 PM
>To: Yu, Lang <Lang.Yu at amd.com>; amd-gfx at lists.freedesktop.org
>Cc: Kuehling, Felix <Felix.Kuehling at amd.com>; Huang, Ray
><Ray.Huang at amd.com>
>Subject: Re: [PATCH] drm/kfd: fix ttm_bo_release warning
>
>Am 23.09.21 um 16:24 schrieb Yu, Lang:
>> [AMD Official Use Only]
>>> -----Original Message-----
>>> From: Koenig, Christian <Christian.Koenig at amd.com>
>>> Sent: Thursday, September 23, 2021 8:24 PM
>>> To: Yu, Lang <Lang.Yu at amd.com>; amd-gfx at lists.freedesktop.org
>>> Cc: Kuehling, Felix <Felix.Kuehling at amd.com>; Christian K nig
>>> <C3B6christian.koenig at amd.com>; Huang, Ray <Ray.Huang at amd.com>
>>> Subject: Re: [PATCH] drm/kfd: fix ttm_bo_release warning
>>>
>>> Am 23.09.21 um 14:09 schrieb Yu, Lang:
>>>> [AMD Official Use Only]
>>>>
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Koenig, Christian <Christian.Koenig at amd.com>
>>>>> Sent: Thursday, September 23, 2021 7:40 PM
>>>>> To: Yu, Lang <Lang.Yu at amd.com>; amd-gfx at lists.freedesktop.org
>>>>> Cc: Kuehling, Felix <Felix.Kuehling at amd.com>; Christian K nig
>>>>> <C3B6christian.koenig at amd.com>; Huang, Ray <Ray.Huang at amd.com>
>>>>> Subject: Re: [PATCH] drm/kfd: fix ttm_bo_release warning
>>>>>
>>>>>
>>>>>
>>>>> Am 23.09.21 um 11:44 schrieb Lang Yu:
>>>>>> If a BO is pinned, unpin it before freeing it.
>>>>>>
>>>>>> Call Trace:
>>>>>> 	ttm_bo_put+0x30/0x50 [ttm]
>>>>>> 	amdgpu_bo_unref+0x1e/0x30 [amdgpu]
>>>>>> 	amdgpu_gem_object_free+0x34/0x50 [amdgpu]
>>>>>> 	drm_gem_object_free+0x1d/0x30 [drm]
>>>>>> 	amdgpu_amdkfd_gpuvm_free_memory_of_gpu+0x31f/0x3a0 [amdgpu]
>>>>>> 	kfd_process_device_free_bos+0xa3/0xf0 [amdgpu]
>>>>>> 	kfd_process_wq_release+0x224/0x2e0 [amdgpu]
>>>>>> 	process_one_work+0x220/0x3c0
>>>>>> 	worker_thread+0x4d/0x3f0
>>>>>> 	kthread+0x114/0x150
>>>>>> 	process_one_work+0x3c0/0x3c0
>>>>>> 	kthread_park+0x90/0x90
>>>>>> 	ret_from_fork+0x22/0x30
>>>>>>
>>>>>> Signed-off-by: Lang Yu <lang.yu at amd.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 3 +++
>>>>>>     1 file changed, 3 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>>>> index 2d6b2d77b738..7e693b064072 100644
>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>>>> @@ -1567,6 +1567,9 @@ int
>>> amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
>>>>>>     	pr_debug("Release VA 0x%llx - 0x%llx\n", mem->va,
>>>>>>     		mem->va + bo_size * (1 + mem->aql_queue));
>>>>>>
>>>>>> +	if (mem->bo->tbo.pin_count)
>>>>>> +		amdgpu_bo_unpin(mem->bo);
>>>>>> +
>>>>> NAK, using mem->bo->tbo.pin_count like this is illegal.
>>>> I didn't  get your point. I referred to function-"void
>>>> amdgpu_bo_unpin(struct amdgpu_bo *bo)", which uses it like this.
>>> What amdgpu_bo_unpin() does is the following:
>>>
>>>          ttm_bo_unpin(&bo->tbo);
>>>          if (bo->tbo.pin_count)
>>>                  return;
>>> ....
>>>
>>> In other words we take further actions based on if the buffer us is
>>> still pinned or not after an unpin operation.
>>>
>>> What you try to do here is unpinning the BO when it is pinned
>>> independent if somebody else or our code has pinned it before.
>> Hi Christian,
>>
>> Thanks for your explanation and advice. I got your point.
>> Actually, these BOs are allocated and pinned during a kfd process lifecycle.
>> I will try to add a flag into struct kgd_mem to indicate which BO is
>> pined and should be unpinned. Which will make
>> amdgpu_bo_pin/amdgpu_bo_unpin calls balanced. Thanks!
>
>That isn't to much better. The real solution would be to unpin them when the kfd
>process is destroyed.

Yes, will unpin them when the kfd process is destroyed.
But we should indicate which BO is pinned and should be unpinned. Right?

Regards,
Lang
 
>Regards,
>Christian.
>
>>
>> Regards,
>> Lang
>>> That can lead to all kind of problems and is clearly illegal.
>>>
>>>>> Where was the BO pinned in the first place?
>>>> I found two places:
>>>>
>>>> 	ret = kfd_process_alloc_gpuvm(pdd, qpd->ib_base, PAGE_SIZE, flags,
>>>> 				      &kaddr);
>>>>
>>>> 	ret = kfd_process_alloc_gpuvm(pdd, qpd->cwsr_base,
>>>> 				      KFD_CWSR_TBA_TMA_SIZE, flags, &kaddr);
>>> Well then you need to figure out where that memory is freed again and
>>> place the unpin appropriately.
>>>
>>> General rule of thumb is that calls to amdgpu_bo_pin/amdgpu_bo_unpin
>>> should be balanced.
>>>
>>> Regards,
>>> Christian.
>>>
>>>> Regards,
>>>> Lang
>>>>
>>>>> Christian.
>>>>>
>>>>>>     	ret = unreserve_bo_and_vms(&ctx, false, false);
>>>>>>
>>>>>>     	/* Remove from VM internal data structures */