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Date:   Wed, 24 Aug 2022 17:14:08 +0200
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Subject: Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic
 locking specification
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To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>,
        David Airlie <airlied@linux.ie>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Daniel Almeida <daniel.almeida@collabora.com>,
        Gert Wollny <gert.wollny@collabora.com>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        Daniel Stone <daniel@fooishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Rob Clark <robdclark@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= <thomas_os@shipmail.org>,
        Qiang Yu <yuq825@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dmitry Osipenko <digetx@gmail.com>,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
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References: <20220824102248.91964-1-dmitry.osipenko@collabora.com>
 <20220824102248.91964-7-dmitry.osipenko@collabora.com>
 <17181951-1b40-cd39-48df-58b43cad117d@amd.com>
 <4af793fd-eccc-ad70-65c3-de78dced71f0@collabora.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
In-Reply-To: <4af793fd-eccc-ad70-65c3-de78dced71f0@collabora.com>
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Am 24.08.22 um 17:03 schrieb Dmitry Osipenko:
> On 8/24/22 17:08, Christian König wrote:
>> Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
>>> Move dma-buf attachment API functions to the dynamic locking
>>> specification.
>>> The strict locking convention prevents deadlock situations for dma-buf
>>> importers and exporters.
>>>
>>> Previously, the "unlocked" versions of the attachment API functions
>>> weren't taking the reservation lock and this patch makes them to take
>>> the lock.
>> Didn't we concluded that we need to keep the attach and detach callbacks
>> without the lock and only move the map/unmap callbacks over?
>>
>> Otherwise it won't be possible for drivers to lock multiple buffers if
>> they have to shuffle things around for a specific attachment.
> We did conclude that. The attach/detach dma-buf ops are unlocked, but
> the map_dma_buf/unmap_dma_buf must be invoked under lock and
> dma_buf_dynamic_attach_unlocked() maps dma-buf if either importer or
> exporter can't handle the dynamic mapping [1].

Ah! You are confusing me over and over again with that :)

Ok in this case that here is fine, I just need to re-read the patch.

Thanks,
Christian.

>
> [1]
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Fv6.0-rc2%2Fsource%2Fdrivers%2Fdma-buf%2Fdma-buf.c%23L869&amp;data=05%7C01%7Cchristian.koenig%40amd.com%7Cdf23d89db8b84bf6d4c008da85e1dc6c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637969502441026991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=d8kWKjDCFn%2B3KmK135Gcv6%2FMLffEYcipouqWxfc%2BKXM%3D&amp;reserved=0
>
> Hence I re-arranged the dma_resv_lock() in
> dma_buf_dynamic_attach_unlocked() to move both pinning and mapping under
> the held lock.
>