On Tue, May 12, 2020 at 09:09:52AM -0300, Jason Gunthorpe wrote: > On Tue, May 12, 2020 at 10:59:29AM +0200, Daniel Vetter wrote: > > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > > index 6802125349fb..d5c0fd2efc70 100644 > > +++ b/drivers/dma-buf/dma-fence.c > > @@ -110,6 +110,52 @@ u64 dma_fence_context_alloc(unsigned num) > > } > > EXPORT_SYMBOL(dma_fence_context_alloc); > > > > +#ifdef CONFIG_LOCKDEP > > +struct lockdep_map dma_fence_lockdep_map = { > > + .name = "dma_fence_map" > > +}; > > + > > +bool dma_fence_begin_signalling(void) > > +{ > > Why is this global? I would have expected it to be connected to a > single fence? It's the same rules for all fences, since they can be shared across drivers in various ways. Lockdep usually achieves that with a static variable hidden in the macro, but that doesn't work if you have lots of different ways from different drivers to create a dma_fence. Hence the unique global one that we explicitly allocate. We have similar stuff for the global dma_resv_lock ww_mutex class, just there it's a bit more standardized and hidden behind a neat macro. But really lockdep needs global lockdep_maps or it doesn't work. > It would also be alot nicer if this was some general lockdep feature, > not tied to dmabuf. This exact problem also strikes anyone using > completions, for instance, and the same solution should be > applicable?? There was: https://lwn.net/Articles/709849/ It even got merged, and seems to have worked. Unfortunately (and I'm not entirely clear on the reasons) it was thrown out again, so we can't use it. That means wait_event/wake_up dependencies need to be manually annotated, like e.g. flush_work() already is. flush_work is more or less where I've stolen this idea from, with some adjustements and tricks on top to make it work for dma_fence users. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx