Re: [PATCH 1/4] mm, notifier: Add a lockdep map for invalidate_range_start/end

From: Jason Gunthorpe
Date: Tue Aug 20 2019 - 09:31:09 EST

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@xxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: "Christian KÃnig" <christian.koenig@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
> include/linux/mmu_notifier.h | 8 ++++++++
> mm/mmu_notifier.c | 9 +++++++++
> 2 files changed, 17 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>