Re: [PATCH v5 00/21] Move all drivers to a common dma-buf locking convention

[Sumit Semwal]

Hi Dmitry,


On Wed, 14 Sept 2022 at 00:58, Dmitry Osipenko
<dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>
> Hello,
>
> This series moves all drivers to a dynamic dma-buf locking specification.
> From now on all dma-buf importers are made responsible for holding
> dma-buf's reservation lock around all operations performed over dma-bufs
> in accordance to the locking specification. This allows us to utilize
> reservation lock more broadly around kernel without fearing of a potential
> deadlocks.
Thank you for the excellent work on this series - apart from a minor
nit in patch 15, please feel free to add my:
Acked-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
for the relevant dma-buf patches (1, 2, 15-19, 21).

Best regards,
Sumit.

>
> This patchset passes all i915 selftests. It was also tested using VirtIO,
> Panfrost, Lima, Tegra, udmabuf, AMDGPU and Nouveau drivers. I tested cases
> of display+GPU, display+V4L and GPU+V4L dma-buf sharing (where appropriate),
> which covers majority of kernel drivers since rest of the drivers share
> same or similar code paths.
>
> Changelog:
>
> v5: - Added acks and r-bs that were given to v4.
>
>     - Changed i915 preparation patch like was suggested by Michael Ruhl.
>       The scope of reservation locking is smaller now.
>
> v4: - Added dma_buf_mmap() to the "locking convention" documentation,
>       which was missed by accident in v3.
>
>     - Added acks from Christian König, Tomasz Figa and Hans Verkuil that
>       they gave to couple v3 patches.
>
>     - Dropped the "_unlocked" postfix from function names that don't have
>       the locked variant, as was requested by Christian König.
>
>     - Factored out the per-driver preparations into separate patches
>       to ease reviewing of the changes, which is now doable without the
>       global dma-buf functions renaming.
>
>     - Factored out the dynamic locking convention enforcements into separate
>       patches which add the final dma_resv_assert_held(dmabuf->resv) to the
>       dma-buf API functions.
>
> v3: - Factored out dma_buf_mmap_unlocked() and attachment functions
>       into aseparate patches, like was suggested by Christian König.
>
>     - Corrected and factored out dma-buf locking documentation into
>       a separate patch, like was suggested by Christian König.
>
>     - Intel driver dropped the reservation locking fews days ago from
>       its BO-release code path, but we need that locking for the imported
>       GEMs because in the end that code path unmaps the imported GEM.
>       So I added back the locking needed by the imported GEMs, updating
>       the "dma-buf attachment locking specification" patch appropriately.
>
>     - Tested Nouveau+Intel dma-buf import/export combo.
>
>     - Tested udmabuf import to i915/Nouveau/AMDGPU.
>
>     - Fixed few places in Etnaviv, Panfrost and Lima drivers that I missed
>       to switch to locked dma-buf vmapping in the drm/gem: Take reservation
>       lock for vmap/vunmap operations" patch. In a result invalidated the
>       Christian's r-b that he gave to v2.
>
>     - Added locked dma-buf vmap/vunmap functions that are needed for fixing
>       vmappping of Etnaviv, Panfrost and Lima drivers mentioned above.
>       I actually had this change stashed for the drm-shmem shrinker patchset,
>       but then realized that it's already needed by the dma-buf patches.
>       Also improved my tests to better cover these code paths.
>
> v2: - Changed locking specification to avoid problems with a cross-driver
>       ww locking, like was suggested by Christian König. Now the attach/detach
>       callbacks are invoked without the held lock and exporter should take the
>       lock.
>
>     - Added "locking convention" documentation that explains which dma-buf
>       functions and callbacks are locked/unlocked for importers and exporters,
>       which was requested by Christian König.
>
>     - Added ack from Tomasz Figa to the V4L patches that he gave to v1.
>
> Dmitry Osipenko (21):
>   dma-buf: Add unlocked variant of vmapping functions
>   dma-buf: Add unlocked variant of attachment-mapping functions
>   drm/gem: Take reservation lock for vmap/vunmap operations
>   drm/prime: Prepare to dynamic dma-buf locking specification
>   drm/armada: Prepare to dynamic dma-buf locking specification
>   drm/i915: Prepare to dynamic dma-buf locking specification
>   drm/omapdrm: Prepare to dynamic dma-buf locking specification
>   drm/tegra: Prepare to dynamic dma-buf locking specification
>   drm/etnaviv: Prepare to dynamic dma-buf locking specification
>   RDMA/umem: Prepare to dynamic dma-buf locking specification
>   misc: fastrpc: Prepare to dynamic dma-buf locking specification
>   xen/gntdev: Prepare to dynamic dma-buf locking specification
>   media: videobuf2: Prepare to dynamic dma-buf locking specification
>   media: tegra-vde: Prepare to dynamic dma-buf locking specification
>   dma-buf: Move dma_buf_vmap() to dynamic locking specification
>   dma-buf: Move dma_buf_attach() to dynamic locking specification
>   dma-buf: Move dma_buf_map_attachment() to dynamic locking
>     specification
>   dma-buf: Move dma_buf_mmap() to dynamic locking specification
>   dma-buf: Document dynamic locking convention
>   media: videobuf2: Stop using internal dma-buf lock
>   dma-buf: Remove obsoleted internal lock
>
>  Documentation/driver-api/dma-buf.rst          |   6 +
>  drivers/dma-buf/dma-buf.c                     | 211 +++++++++++++++---
>  drivers/gpu/drm/armada/armada_gem.c           |   8 +-
>  drivers/gpu/drm/drm_client.c                  |   4 +-
>  drivers/gpu/drm/drm_gem.c                     |  24 ++
>  drivers/gpu/drm/drm_gem_dma_helper.c          |   6 +-
>  drivers/gpu/drm/drm_gem_framebuffer_helper.c  |   6 +-
>  drivers/gpu/drm/drm_gem_ttm_helper.c          |   9 +-
>  drivers/gpu/drm/drm_prime.c                   |   6 +-
>  drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c   |   2 +-
>  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    |   2 +-
>  drivers/gpu/drm/i915/gem/i915_gem_object.c    |  14 ++
>  .../drm/i915/gem/selftests/i915_gem_dmabuf.c  |  16 +-
>  drivers/gpu/drm/lima/lima_sched.c             |   4 +-
>  drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c     |   4 +-
>  drivers/gpu/drm/panfrost/panfrost_dump.c      |   4 +-
>  drivers/gpu/drm/panfrost/panfrost_perfcnt.c   |   6 +-
>  drivers/gpu/drm/qxl/qxl_object.c              |  17 +-
>  drivers/gpu/drm/qxl/qxl_prime.c               |   4 +-
>  drivers/gpu/drm/tegra/gem.c                   |  17 +-
>  drivers/infiniband/core/umem_dmabuf.c         |   7 +-
>  .../common/videobuf2/videobuf2-dma-contig.c   |  22 +-
>  .../media/common/videobuf2/videobuf2-dma-sg.c |  19 +-
>  .../common/videobuf2/videobuf2-vmalloc.c      |  17 +-
>  .../platform/nvidia/tegra-vde/dmabuf-cache.c  |   6 +-
>  drivers/misc/fastrpc.c                        |   6 +-
>  drivers/xen/gntdev-dmabuf.c                   |   8 +-
>  include/drm/drm_gem.h                         |   3 +
>  include/linux/dma-buf.h                       |  17 +-
>  29 files changed, 320 insertions(+), 155 deletions(-)
>
> --
> 2.37.3
>


--
Thanks and regards,

Sumit Semwal (he / him)
Tech Lead - LCG, Vertical Technologies
Linaro.org │ Open source software for ARM SoCs