linux-kernel - Re: [Linaro-mm-sig] [PATCH v2 3/5] dma-buf: Move all dma-bufs to dynamic locking specification

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Date:   Fri, 12 Aug 2022 13:34:02 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Christian König <christian.koenig@....com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org,
        spice-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Daniel Almeida <daniel.almeida@...labora.com>,
        Gert Wollny <gert.wollny@...labora.com>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rob Clark <robdclark@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Thomas Hellström <thomas_os@...pmail.org>
Subject: Re: [Linaro-mm-sig] [PATCH v2 3/5] dma-buf: Move all dma-bufs to
 dynamic locking specification



Am 10.08.22 um 20:53 schrieb Dmitry Osipenko:
> On 8/10/22 21:25, Christian König wrote:
>> Am 10.08.22 um 19:49 schrieb Dmitry Osipenko:
>>> On 8/10/22 14:30, Christian König wrote:
>>>> Am 25.07.22 um 17:18 schrieb Dmitry Osipenko:
>>>>> This patch moves the non-dynamic dma-buf users over to the dynamic
>>>>> locking specification. The strict locking convention prevents deadlock
>>>>> situation for dma-buf importers and exporters.
>>>>>
>>>>> Previously the "unlocked" versions of the dma-buf API functions weren't
>>>>> taking the reservation lock and this patch makes them to take the lock.
>>>>>
>>>>> Intel and AMD GPU drivers already were mapping imported dma-bufs under
>>>>> the held lock, hence the "locked" variant of the functions are added
>>>>> for them and the drivers are updated to use the "locked" versions.
>>>> In general "Yes, please", but that won't be that easy.
>>>>
>>>> You not only need to change amdgpu and i915, but all drivers
>>>> implementing the map_dma_buf(), unmap_dma_buf() callbacks.
>>>>
>>>> Auditing all that code is a huge bunch of work.
>>> Hm, neither of drivers take the resv lock in map_dma_buf/unmap_dma_buf.
>>> It's easy to audit them all and I did it. So either I'm missing
>>> something or it doesn't take much time to check them all. Am I really
>>> missing something?
>> Ok, so this is only changing map/unmap now?
> It also vmap/vunmap and attach/detach: In the previous patch I added the
> _unlocked postfix to the func names and in this patch I made them all to
> actually take the lock.


Take your patch "[PATCH v2 2/5] drm/gem: Take reservation lock for 
vmap/vunmap operations" as a blueprint on how to approach it.

E.g. one callback at a time and then document the result in the end.

Regards,
Christian.

>
>> In this case please separate this from the documentation change.
> I'll factor out the doc in the v3.
>
>> I would also drop the _locked postfix from the function name, just
>> having _unlocked on all functions which are supposed to be called with
>> the lock held should be sufficient.
> Noted for the v3.
>
>> Thanks for looking into this,
>> Christian.
> Thank you for the review.
>