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:   Wed, 10 Aug 2022 20:49:52 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Christian König <ckoenig.leichtzumerken@...il.com>,
        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>,
        Christian König <christian.koenig@....com>,
        "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>
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
Subject: Re: [Linaro-mm-sig] [PATCH v2 3/5] dma-buf: Move all dma-bufs to
 dynamic locking specification

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?

https://elixir.bootlin.com/linux/latest/A/ident/map_dma_buf

-- 
Best regards,
Dmitry