On Tue, May 21, 2019 at 5:41 PM Jerome Glisse <jglisse@xxxxxxxxxx> wrote: > > On Mon, May 20, 2019 at 11:39:45PM +0200, Daniel Vetter wrote: > > This is a similar idea to the fs_reclaim fake lockdep lock. It's > > fairly easy to provoke a specific notifier to be run on a specific > > range: Just prep it, and then munmap() it. > > > > A bit harder, but still doable, is to provoke the mmu notifiers for > > all the various callchains that might lead to them. But both at the > > same time is really hard to reliable hit, especially when you want to > > exercise paths like direct reclaim or compaction, where it's not > > easy to control what exactly will be unmapped. > > > > By introducing a lockdep map to tie them all together we allow lockdep > > to see a lot more dependencies, without having to actually hit them > > in a single challchain while testing. > > > > Aside: Since I typed this to test i915 mmu notifiers I've only rolled > > this out for the invaliate_range_start callback. If there's > > interest, we should probably roll this out to all of them. But my > > undestanding of core mm is seriously lacking, and I'm not clear on > > whether we need a lockdep map for each callback, or whether some can > > be shared. > > I need to read more on lockdep but it is legal to have mmu notifier > invalidation within each other. For instance when you munmap you > might split a huge pmd and it will trigger a second invalidate range > while the munmap one is not done yet. Would that trigger the lockdep > here ? Depends how it's nesting. I'm wrapping the annotation only just around the individual mmu notifier callback, so if the nesting is just - munmap starts - invalidate_range_start #1 - we noticed that there's a huge pmd we need to split - invalidate_range_start #2 - invalidate_reange_end #2 - invalidate_range_end #1 - munmap is done But if otoh it's ok to trigger the 2nd invalidate range from within an mmu_notifier->invalidate_range_start callback, then lockdep will be pissed about that. > Worst case i can think of is 2 invalidate_range_start chain one after > the other. I don't think you can triggers a 3 levels nesting but maybe. Lockdep has special nesting annotations. I think it'd be more an issue of getting those funneled through the entire call chain, assuming we really need that. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
