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Subject: Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers
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From: John Hubbard <jhubbard@nvidia.com>
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Date: Wed, 7 Oct 2020 14:36:52 -0700
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To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: DRI Development <dri-devel@lists.freedesktop.org>, LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org, Linux MM <linux-mm@kvack.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-samsung-soc <linux-samsung-soc@vger.kernel.org>, "open list:DMA BUFFER SHARING FRAMEWORK" <linux-media@vger.kernel.org>, linux-s390@vger.kernel.org, Daniel Vetter <daniel.vetter@intel.com>, Jason Gunthorpe <jgg@ziepe.ca>, Inki Dae <inki.dae@samsung.com>, Joonyoung Shim <jy0922.shim@samsung.com>, Seung-Woo Kim <sw0312.kim@samsung.com>, Kyungmin Park <kyungmin.park@samsung.com>, Kukjin Kim <kgene@kernel.org>, Krzysztof Kozlowski <krzk@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, Jan Kara <jack@suse.cz>, Dan Williams <dan.j.williams@intel.com>

On 10/7/20 2:32 PM, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 10:33 PM John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> On 10/7/20 9:44 AM, Daniel Vetter wrote:
...
>>> @@ -398,15 +399,11 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d,
>>>        dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt,
>>>                          DMA_BIDIRECTIONAL, 0);
>>>
>>> -     pages = frame_vector_pages(g2d_userptr->vec);
>>> -     if (!IS_ERR(pages)) {
>>> -             int i;
>>> +     for (i = 0; i < g2d_userptr->npages; i++)
>>> +             set_page_dirty_lock(g2d_userptr->pages[i]);
>>>
>>> -             for (i = 0; i < frame_vector_count(g2d_userptr->vec); i++)
>>> -                     set_page_dirty_lock(pages[i]);
>>> -     }
>>> -     put_vaddr_frames(g2d_userptr->vec);
>>> -     frame_vector_destroy(g2d_userptr->vec);
>>> +     unpin_user_pages(g2d_userptr->pages, g2d_userptr->npages);
>>> +     kvfree(g2d_userptr->pages);
>>
>> You can avoid writing your own loop, and just simplify the whole thing down to
>> two lines:
>>
>>          unpin_user_pages_dirty_lock(g2d_userptr->pages, g2d_userptr->npages,
>>                                      true);
>>          kvfree(g2d_userptr->pages);
> 
> Oh nice, this is neat. I'll also roll it out in the habanalabs patch,
> that has the same thing. Well almost, it only uses set_page_dirty, not
> the _lock variant. But I have no idea whether that matters or not?


It matters. And invariably, call sites that use set_page_dirty() instead
of set_page_dirty_lock() were already wrong.  Which is why I never had to
provide anything like "unpin_user_pages_dirty (not locked)".

Although in habanalabs case, I just reviewed patch 3 and I think they *were*
correctly using set_page_dirty_lock()...

thanks,
-- 
John Hubbard
NVIDIA