On Thu, May 12, 2022 at 09:29:35AM +0200, Christian König wrote: > Am 11.05.22 um 21:05 schrieb Daniel Vetter: > > [SNIP] > > > > > It's unclear to me which driver may ever want to do the mapping under > > > > > the dma_resv_lock. But if we will ever have such a driver that will need > > > > > to map imported buffer under dma_resv_lock, then we could always add the > > > > > dma_buf_vmap_locked() variant of the function. In this case the locking > > > > > rule will sound like this: > > > > > > > > > > "All dma-buf importers are responsible for holding the dma-reservation > > > > > lock around the dmabuf->ops->mmap/vmap() calls." > > > Are you okay with this rule? > > Yeah I think long-term it's where we want to be, just trying to find > > clever ways to get there. > > > > And I think Christian agrees with that? > > Yes, completely. > > A design where most DMA-buf functions are supposed to be called with the > reservation lock held is exactly what I have in mind for the long term. > > > > > > > It shouldn't be that hard to clean up. The last time I looked into it my > > > > > > main problem was that we didn't had any easy unit test for it. > > > > > Do we have any tests for dma-bufs at all? It's unclear to me what you > > > > > are going to test in regards to the reservation locks, could you please > > > > > clarify? > > > > Unfortunately not really :-/ Only way really is to grab a driver which > > > > needs vmap (those are mostly display drivers) on an imported buffer, and > > > > see what happens. > > > > > > > > 2nd best is liberally sprinkling lockdep annotations all over the place > > > > and throwing it at intel ci (not sure amd ci is accessible to the public) > > > > and then hoping that's good enough. Stuff like might_lock and > > > > dma_resv_assert_held. > > > Alright > > So throwing it at intel-gfx-ci can't hurt I think, but that only covers > > i915 so doesn't really help with the bigger issue of catching all the > > drivers. > > BTW: We have now somebody working on converting the existing libdrm_amdgpu > unit tests over to igt. This sounds awesome. /me throws a happy dance Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
