On Tue, Aug 20, 2019 at 10:18:59AM +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.
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.
v2: Use lock_map_acquire/release() like fs_reclaim, to avoid confusion with this being a real mutex (Chris Wilson).
v3: Rebase on top of Glisse's arg rework.
v4: Also annotate invalidate_range_end (Jason Gunthorpe) Also annotate invalidate_range_start_nonblock, I somehow missed that one in the first version.
Cc: Jason Gunthorpe jgg@ziepe.ca Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Andrew Morton akpm@linux-foundation.org Cc: David Rientjes rientjes@google.com Cc: "Jérôme Glisse" jglisse@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: "Christian König" christian.koenig@amd.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: linux-mm@kvack.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com
include/linux/mmu_notifier.h | 8 ++++++++ mm/mmu_notifier.c | 9 +++++++++ 2 files changed, 17 insertions(+)
Reviewed-by: Jason Gunthorpe jgg@mellanox.com
Jason