[PATCH v3 3/4] mm/mmap: Change detached vma locking scheme

[Liam R. Howlett]

Don't set the lock to the mm lock so that the detached VMA tree does not
complain about being unlocked when the mmap_lock is dropped prior to
freeing the tree.

Introduce mt_on_stack() for setting the external lock to NULL only when
LOCKDEP is used.

Move the destroying of the detached tree outside the mmap lock all
together.

Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 include/linux/maple_tree.h | 3 +++
 mm/mmap.c                  | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 6618c1512886..e278b9598428 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -187,10 +187,13 @@ typedef struct lockdep_map *lockdep_map_p;
=20
 #define mt_set_external_lock(mt, lock)					\
 	(mt)->ma_external_lock =3D &(lock)->dep_map
+
+#define mt_on_stack(mt)			(mt).ma_external_lock =3D NULL
 #else
 typedef struct { /* nothing */ } lockdep_map_p;
 #define mt_lock_is_held(mt)	1
 #define mt_set_external_lock(mt, lock)	do { } while (0)
+#define mt_on_stack(mt)			do { } while (0)
 #endif
=20
 /*
diff --git a/mm/mmap.c b/mm/mmap.c
index 7b70379a8b3e..18971ab91633 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2427,7 +2427,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct =
vm_area_struct *vma,
 	unsigned long locked_vm =3D 0;
 	MA_STATE(mas_detach, &mt_detach, 0, 0);
 	mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
-	mt_set_external_lock(&mt_detach, &mm->mmap_lock);
+	mt_on_stack(mt_detach);
=20
 	/*
 	 * If we need to split any vma, do it now to save pain later.
@@ -2545,11 +2545,11 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struc=
t vm_area_struct *vma,
 	/* Statistics and freeing VMAs */
 	mas_set(&mas_detach, start);
 	remove_mt(mm, &mas_detach);
-	__mt_destroy(&mt_detach);
 	validate_mm(mm);
 	if (unlock)
 		mmap_read_unlock(mm);
=20
+	__mt_destroy(&mt_detach);
 	return 0;
=20
 clear_tree_failed:
--=20
2.39.2


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