linux-kernel - Re: [PATCH v10 07/11] drm/shmem-helper: Switch to reservation lock

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Message-ID: <c185946a-0a59-9f6e-9592-20b93f45514e@collabora.com>
Date:   Fri, 17 Feb 2023 16:33:00 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        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>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Rob Herring <robh@...nel.org>, Sean Paul <sean@...rly.run>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v10 07/11] drm/shmem-helper: Switch to reservation lock

On 2/17/23 15:52, Thomas Zimmermann wrote:
> Hi
> 
> Am 08.01.23 um 22:04 schrieb Dmitry Osipenko:
>> Replace all drm-shmem locks with a GEM reservation lock. This makes locks
>> consistent with dma-buf locking convention where importers are
>> responsible
>> for holding reservation lock for all operations performed over dma-bufs,
>> preventing deadlock between dma-buf importers and exporters.
>>
>> Suggested-by: Daniel Vetter <daniel@...ll.ch>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> 
> How much testing has this patch seen?
> 
> I'm asking because when I tried to fix the locking in this code, I had
> to review every importer to make sure that it aquired the lock. Has this
> problem been resolved?

The dma-buf locking rules was merged to v6.2 kernel.

I tested all the available importers that use drm-shmem. There were
deadlocks and lockdep warnings while I was working/testing the importer
paths in the past, feel confident that the code paths were tested well
enough. Note that Lima and Panfrost always use the importer paths in
case of display because display is a separate driver.

I checked that:

- desktop environment works
- 3d works
- video dec (v4l2) dmabuf sharing works
- shrinker works

I.e. tested it all with VirtIO-GPU, Panfrost and Lima drivers. For
VirtIO-GPU importer paths aren't relevant because it can only share bufs
with other virtio driver and in upstream we only have VirtIO-GPU driver
supporting dma-bufs.

-- 
Best regards,
Dmitry