Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

From: "Christian König via Virtualization" <virtualization@lists.linux-foundation.org>
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>,
	"Thomas Hellström" <thomas_os@shipmail.org>,
	"Qiang Yu" <yuq825@gmail.com>
Cc: lima@lists.freedesktop.org, linux-rdma@vger.kernel.org,
	linux-arm-msm@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
	virtualization@lists.linux-foundation.org,
	linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org,
	Dmitry Osipenko <digetx@gmail.com>,
	kernel@collabora.com, linux-media@vger.kernel.org
Subject: Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification
Date: Wed, 24 Aug 2022 17:14:08 +0200	[thread overview]
Message-ID: <b24017e9-e8e7-148e-951b-0f2a1dffdca7@amd.com> (raw)
In-Reply-To: <4af793fd-eccc-ad70-65c3-de78dced71f0@collabora.com>

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.
>

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