Re: [PATCH v4 00/21] Move all drivers to a common dma-buf locking convention

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Hi Dmitry,

I've gone over this multiple times now and while it is still possible that we missed something I think that this should land now.

The whole topic is just to complicated that we can 100% sure guarantee that there isn't anything wrong with the locking, but lockdep and driver testing should allow us to quickly find remaining issues.

Do you have commit rights to drm-misc-next or should I push it?

Thanks,
Christian.

Am 31.08.22 um 17:37 schrieb Dmitry Osipenko:
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.

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:

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    |  12 +
  .../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, 318 insertions(+), 155 deletions(-)





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