02.09.2022 13:31, Dmitry Osipenko пишет: > 01.09.2022 17:02, Ruhl, Michael J пишет: > ... >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >>> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >>> drm_i915_private *i915, >>> continue; >>> } >>> >>> + /* >>> + * dma_buf_unmap_attachment() requires reservation to be >>> + * locked. The imported GEM shouldn't share reservation lock, >>> + * so it's safe to take the lock. >>> + */ >>> + if (obj->base.import_attach) >>> + i915_gem_object_lock(obj, NULL); >> >> There is a lot of stuff going here. Taking the lock may be premature... >> >>> __i915_gem_object_pages_fini(obj); >> >> The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where >> unmap_attachment is actually called, would it make more sense to make >> do the locking there? > > The __i915_gem_object_put_pages() is invoked with a held reservation > lock, while freeing object is a special time when we know that GEM is > unused. > > The __i915_gem_free_objects() was taking the lock two weeks ago until > the change made Chris Wilson [1] reached linux-next. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=2826d447fbd60e6a05e53d5f918bceb8c04e315c > > I don't think we can take the lock within > i915_gem_object_put_pages_dmabuf(), it may/should deadlock other code paths. On the other hand, we can check whether the GEM's refcount number is zero in i915_gem_object_put_pages_dmabuf() and then take the lock if it's zero. Also, seems it should be possible just to bail out from i915_gem_object_put_pages_dmabuf() if refcount=0. The further drm_prime_gem_destroy() will take care of unmapping. Perhaps this could be the best option, I'll give it a test.
