The old code was always doing:
vma->vm_end = next->vm_end
vma_rb_erase(next) // in __vma_unlink
vma->vm_next = next->vm_next // in __vma_unlink
next = vma->vm_next
vma_gap_update(next)
The new code still does the above for remove_next == 1 and 2, but for
remove_next == 3 it has been changed and it does:
next->vm_start = vma->vm_start
vma_rb_erase(vma) // in __vma_unlink
vma_gap_update(next)
In the latter case, while unlinking "vma", validate_mm_rb() is told to
ignore "vma" that is being removed, but next->vm_start was reduced
instead. So for the new case, to avoid the false positive from
validate_mm_rb, it should be "next" that is ignored when "vma" is
being unlinked.
"vma" and "next" in the above comment, considered pre-swap().
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
mm/mmap.c | 59 +++++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 41 insertions(+), 18 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 1b88754..57b1eaf 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -398,15 +398,9 @@ static inline void vma_rb_insert(struct vm_area_struct *vma,
rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}
-static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
+static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
{
/*
- * All rb_subtree_gap values must be consistent prior to erase,
- * with the possible exception of the vma being erased.
- */
- validate_mm_rb(root, vma);
-
- /*
* Note rb_erase_augmented is a fairly large inline function,
* so make sure we instantiate it only once with our desired
* augmented rbtree callbacks.
@@ -414,6 +408,32 @@ static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}
+static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
+ struct rb_root *root,
+ struct vm_area_struct *ignore)
+{
+ /*
+ * All rb_subtree_gap values must be consistent prior to erase,
+ * with the possible exception of the "next" vma being erased if
+ * next->vm_start was reduced.
+ */
+ validate_mm_rb(root, ignore);
+
+ __vma_rb_erase(vma, root);
+}
+
+static __always_inline void vma_rb_erase(struct vm_area_struct *vma,
+ struct rb_root *root)
+{
+ /*
+ * All rb_subtree_gap values must be consistent prior to erase,
+ * with the possible exception of the vma being erased.
+ */
+ validate_mm_rb(root, vma);
+
+ __vma_rb_erase(vma, root);
+}
+
/*
* vma has some anon_vma assigned, and is already inserted on that
* anon_vma's interval trees.
@@ -600,11 +620,12 @@ static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
static __always_inline void __vma_unlink_common(struct mm_struct *mm,
struct vm_area_struct *vma,
struct vm_area_struct *prev,
- bool has_prev)
+ bool has_prev,
+ struct vm_area_struct *ignore)
{
struct vm_area_struct *next;
- vma_rb_erase(vma, &mm->mm_rb);
+ vma_rb_erase_ignore(vma, &mm->mm_rb, ignore);
next = vma->vm_next;
if (has_prev)
prev->vm_next = next;
@@ -626,13 +647,7 @@ static inline void __vma_unlink_prev(struct mm_struct *mm,
struct vm_area_struct *vma,
struct vm_area_struct *prev)
{
- __vma_unlink_common(mm, vma, prev, true);
-}
-
-static inline void __vma_unlink(struct mm_struct *mm,
- struct vm_area_struct *vma)
-{
- __vma_unlink_common(mm, vma, NULL, false);
+ __vma_unlink_common(mm, vma, prev, true, vma);
}
/*
@@ -811,8 +826,16 @@ again:
if (remove_next != 3)
__vma_unlink_prev(mm, next, vma);
else
- /* vma is not before next if they've been swapped */
- __vma_unlink(mm, next);
+ /*
+ * vma is not before next if they've been
+ * swapped.
+ *
+ * pre-swap() next->vm_start was reduced so
+ * tell validate_mm_rb to ignore pre-swap()
+ * "next" (which is stored in post-swap()
+ * "vma").
+ */
+ __vma_unlink_common(mm, next, NULL, false, vma);
if (file)
__remove_shared_vm_struct(next, file, mapping);
} else if (insert) {
--
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