Re: [PATCH v3 04/12] drm/ttm: Set dma addr to null after freee

From: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
To: christian.koenig@amd.com, amd-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org, daniel.vetter@ffwll.ch,
	robh@kernel.org, l.stach@pengutronix.de, yuq825@gmail.com,
	eric@anholt.net
Cc: Alexander.Deucher@amd.com, gregkh@linuxfoundation.org
Subject: Re: [PATCH v3 04/12] drm/ttm: Set dma addr to null after freee
Date: Mon, 23 Nov 2020 00:15:38 -0500	[thread overview]
Message-ID: <dd7e107a-d1c0-404d-81d6-7ecca358cd8e@amd.com> (raw)
In-Reply-To: <cc970f95-ae21-ab8d-232e-abbddf7d6a0f@gmail.com>

On 11/21/20 9:13 AM, Christian König wrote:
> Am 21.11.20 um 06:21 schrieb Andrey Grodzovsky:
>> Fixes oops.
>
> That file doesn't even exist any more. What oops should this fix?

Which file ?
We set dma_address to NULL in every other place after unmap. This is so that
if dma address was already unmapped we skip it next time we enter 
ttm_unmap_and_unpopulate_pages
with same tt for some reason.
The oops happens with IOMMU enabled. The device is removed from it's IOMMU group
during PCI remove but the BOs are all still alive if user mode client holds 
reference to drm file.
Later when the refernece is droppped and device fini happens i get oops in
ttm_unmap_and_unpopulate_pages->dma_unmap_page becaue of IOMMU group structures 
being gone already.
Patch  [11/12] drm/amdgpu: Register IOMMU topology notifier per device together 
with this patch solve the oops.

Andrey

>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
>> ---
>>   drivers/gpu/drm/ttm/ttm_page_alloc.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c 
>> b/drivers/gpu/drm/ttm/ttm_page_alloc.c
>> index b40a467..b0df328 100644
>> --- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
>> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
>> @@ -1160,6 +1160,8 @@ void ttm_unmap_and_unpopulate_pages(struct device *dev, 
>> struct ttm_dma_tt *tt)
>>           dma_unmap_page(dev, tt->dma_address[i], num_pages * PAGE_SIZE,
>>                      DMA_BIDIRECTIONAL);
>>   +        tt->dma_address[i] = 0;
>> +
>>           i += num_pages;
>>       }
>>       ttm_pool_unpopulate(&tt->ttm);
>
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