[PATCH v2 0/7] Move dma-buf mmap() reservation locking down to exporters

[Dmitry Osipenko]

This patchset makes dma-buf exporters responisble for taking care of
the reservation lock. I also included patch that moves drm-shmem to use
reservation lock, to let CI test the whole set. I'm going to take all
the patches via the drm-misc tree, please give an ack.

Previous policy stated that dma-buf core takes the lock around mmap()
callback. Which meant that both importers and exporters shouldn't touch
the reservation lock in the mmap() code path. This worked well until
Intel-CI found a deadlock problem in a case of self-imported dma-buf [1].

The problem happens when userpace mmaps a self-imported dma-buf, i.e.
mmaps the dma-buf FD. DRM core treats self-imported dma-bufs as own GEMs
[2]. There is no way to differentiate a prime GEM from a normal GEM for
drm-shmem in drm_gem_shmem_mmap(), which resulted in a deadlock problem
for drm-shmem mmap() code path once it's switched to use reservation lock.

It was difficult to fix the drm-shmem problem without adjusting dma-buf
locking policy. In parctice not much changed from importers perspective
because previosly dma-buf was taking the lock in between of importers
and exporters. Now this lock is shifted down to exporters.

[1] https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_114671v2/shard-snb5/igt@prime_vgem@sync@xxxxxxxxx
[2] https://elixir.bootlin.com/linux/v6.3-rc4/source/drivers/gpu/drm/drm_prime.c#L924

Changelog:

v2: - Added ack from Christian König to the DRM patch.

    - Dropped "fixes" tag from the patches, like was requested by
      Christian König. The patches don't actually need a backport
      and merely improve the locking policy.

    - Dropped "reverts" from the patch titles to prevent them from
      auto-backporting by the stable bot based on the title.

    - Added r-b from Emil Velikov and placed the drm_WARN in the
      drm-shmem patch like he suggested in a comment to v1.

    - Corrected drm-shmem patch dma_resv_lock(obj->resv) inconsistently
      used with dma_resv_unlock(shmem->base.resv). Now shmem->base.resv
      variant is used for all locks/unlocks.

Dmitry Osipenko (7):
  media: videobuf2: Don't assert held reservation lock for dma-buf
    mmapping
  dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping
  udmabuf: Don't assert held reservation lock for dma-buf mmapping
  fastrpc: Don't assert held reservation lock for dma-buf mmapping
  drm: Don't assert held reservation lock for dma-buf mmapping
  dma-buf: Change locking policy for mmap()
  drm/shmem-helper: Switch to reservation lock

 drivers/dma-buf/dma-buf.c                     |  17 +-
 drivers/dma-buf/heaps/cma_heap.c              |   3 -
 drivers/dma-buf/heaps/system_heap.c           |   3 -
 drivers/dma-buf/udmabuf.c                     |   2 -
 drivers/gpu/drm/drm_gem_shmem_helper.c        | 208 ++++++++----------
 drivers/gpu/drm/drm_prime.c                   |   2 -
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    |   2 -
 drivers/gpu/drm/lima/lima_gem.c               |   8 +-
 drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c     |   2 -
 drivers/gpu/drm/panfrost/panfrost_drv.c       |   7 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   6 +-
 drivers/gpu/drm/panfrost/panfrost_mmu.c       |  19 +-
 drivers/gpu/drm/tegra/gem.c                   |   2 -
 .../common/videobuf2/videobuf2-dma-contig.c   |   3 -
 .../media/common/videobuf2/videobuf2-dma-sg.c |   3 -
 .../common/videobuf2/videobuf2-vmalloc.c      |   3 -
 drivers/misc/fastrpc.c                        |   3 -
 include/drm/drm_gem_shmem_helper.h            |  14 +-
 18 files changed, 117 insertions(+), 190 deletions(-)

-- 
2.39.2