To ensure cross-driver locking compatibility, document the expected guidelines for implementing the GEM locking in i915. Note that this is a description of how things should end up after being reworked, and does not reflect the current state of things. Signed-off-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Dave Airlie <airlied@xxxxxxxxxx> Cc: Matthew Auld <matthew.auld@xxxxxxxxx> Cc: Abdiel Janulgue <abdiel.janulgue@xxxxxxxxxxxxxxx> Cc: CQ Tang <cq.tang@xxxxxxxxx> --- Documentation/gpu/i915.rst | 45 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst index e249ea7b0ec7..63a72d10f2c7 100644 --- a/Documentation/gpu/i915.rst +++ b/Documentation/gpu/i915.rst @@ -320,6 +320,51 @@ for execution also include a list of all locations within buffers that refer to GPU-addresses so that the kernel can edit the buffer correctly. This process is dubbed relocation. +Locking Guidelines +------------------ + +**NOTE:** This is a description of how the locking should be after +refactoring is done. Does not necessarily reflect what the locking +looks like while WIP. + +#. All locking rules and interface contracts with cross-driver interfaces + (dma-buf, dma_fence) need to be followed. + +#. No struct_mutex anywhere in the code + +#. dma_resv will be the outermost lock (when needed) and ww_acquire_ctx + is to be hoisted at highest level and passed down within i915_gem_ctx + in the call chain + +#. While holding lru/memory manager (buddy, drm_mm, whatever) locks + system memory allocations are not allowed + + * Enforce this by priming lockdep (with fs_reclaim). If we + allocate memory while holding these looks we get a rehash + of the shrinker vs. struct_mutex saga, and that would be + real bad. + +#. Do not nest different lru/memory manager locks within each other. + Take them in turn to update memory allocations, relying on the object’s + dma_resv ww_mutex to serialize against other operations. + +#. The suggestion for lru/memory managers locks is that they are small + enough to be spinlocks. + +#. All features need to come with exhaustive kernel selftests and/or + IGT tests when appropriate + +#. All LMEM uAPI paths need to be fully restartable (_interruptible() + for all locks/waits/sleeps) + + * Error handling validation through signal injection. + Still the best strategy we have for validating GEM uAPI + corner cases. + Must be excessively used in the IGT, and we need to check + that we really have full path coverage of all error cases. + + * -EDEADLK handling with ww_mutex + GEM BO Management Implementation Details ---------------------------------------- -- 2.20.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
