[PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start

[Daniel Vetter]

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.

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.

Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: David Rientjes <rientjes at google.com>
Cc: "Jérôme Glisse" <jglisse at redhat.com>
Cc: Michal Hocko <mhocko at suse.com>
Cc: "Christian König" <christian.koenig at amd.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: linux-mm at kvack.org
Reviewed-by: Jérôme Glisse <jglisse at redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 include/linux/mmu_notifier.h | 6 ++++++
 mm/mmu_notifier.c            | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index b6c004bd9f6a..9dd38c32fc53 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -42,6 +42,10 @@ enum mmu_notifier_event {
 
 #ifdef CONFIG_MMU_NOTIFIER
 
+#ifdef CONFIG_LOCKDEP
+extern struct lockdep_map __mmu_notifier_invalidate_range_start_map;
+#endif
+
 /*
  * The mmu notifier_mm structure is allocated and installed in
  * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
@@ -310,10 +314,12 @@ static inline void mmu_notifier_change_pte(struct mm_struct *mm,
 static inline void
 mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
 {
+	lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
 	if (mm_has_notifiers(range->mm)) {
 		range->flags |= MMU_NOTIFIER_RANGE_BLOCKABLE;
 		__mmu_notifier_invalidate_range_start(range);
 	}
+	lock_map_release(&__mmu_notifier_invalidate_range_start_map);
 }
 
 static inline int
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 43a76d030164..331e43ce6f3c 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -21,6 +21,13 @@
 /* global SRCU for all MMs */
 DEFINE_STATIC_SRCU(srcu);
 
+#ifdef CONFIG_LOCKDEP
+struct lockdep_map __mmu_notifier_invalidate_range_start_map = {
+	.name = "mmu_notifier_invalidate_range_start"
+};
+EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start_map);
+#endif
+
 /*
  * This function allows mmu_notifier::release callback to delay a call to
  * a function that will free appropriate resources. The function must be
-- 
2.22.0