mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end
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 reliably 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. On Jason's suggestion this is is rolled out for both invalidate_range_start and invalidate_range_end. They both have the same calling context, hence we can share the same lockdep map. Note that the annotation for invalidate_ranage_start is outside of the mm_has_notifiers(), to make sure lockdep is informed about all paths leading to this context irrespective of whether mmu notifiers are present for a given context. We don't do that on the invalidate_range_end side to avoid paying the overhead twice, there the lockdep annotation is pushed down behind the mm_has_notifiers() check. Link: https://lore.kernel.org/r/20190826201425.17547-2-daniel.vetter@ffwll.ch Reviewed-by:Jason Gunthorpe <jgg@mellanox.com> Signed-off-by:
Daniel Vetter <daniel.vetter@intel.com> Signed-off-by:
Jason Gunthorpe <jgg@mellanox.com>
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