RE: [PATCH] drm/kfd: fix ttm_bo_release warning

["Yu, Lang" <Lang.Yu@amd.com>]

[AMD Official Use Only]


>-----Original Message-----
>From: Koenig, Christian <Christian.Koenig@amd.com>
>Sent: Thursday, September 23, 2021 8:24 PM
>To: Yu, Lang <Lang.Yu@amd.com>; amd-gfx@lists.freedesktop.org
>Cc: Kuehling, Felix <Felix.Kuehling@amd.com>; Christian K nig
><C3B6christian.koenig@amd.com>; Huang, Ray <Ray.Huang@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@amd.com>
>>> Sent: Thursday, September 23, 2021 7:40 PM
>>> To: Yu, Lang <Lang.Yu@amd.com>; amd-gfx@lists.freedesktop.org
>>> Cc: Kuehling, Felix <Felix.Kuehling@amd.com>; Christian K nig
>>> <C3B6christian.koenig@amd.com>; Huang, Ray <Ray.Huang@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@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!

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 */