[PATCH v3 45/48] mm/mmap: Introduce dup_vma_anon() helper

Liam Howlett
2023-01-17T02:40:12Z

Create a helper for duplicating the anon vma when adjusting the vma.
This simplifies the logic of __vma_adjust().

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
mm/mmap.c | 74 ++++++++++++++++++++++++++++++-------------------------
1 file changed, 40 insertions(+), 34 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index a6e07edc15e9..a533e39a669c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -620,6 +620,29 @@ static inline void vma_complete(struct vma_prepare *vp,
uprobe_mmap(vp->insert);
}

+/*
+ * dup_anon_vma() - Helper function to duplicate anon_vma
+ * @dst: The destination VMA
+ * @src: The source VMA
+ *
+ * Returns: 0 on success.
+ */
+static inline int dup_anon_vma(struct vm_area_struct *dst,
+ struct vm_area_struct *src)
+{
+ /*
+ * Easily overlooked: when mprotect shifts the boundary, make sure the
+ * expanding vma has anon_vma set if the shrinking vma had, to cover any
+ * anon pages imported.
+ */
+ if (src->anon_vma && !dst->anon_vma) {
+ dst->anon_vma = src->anon_vma;
+ return anon_vma_clone(dst, src);
+ }
+
+ return 0;
+}
+
/*
* vma_expand - Expand an existing VMA
*
@@ -645,15 +668,12 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
struct vma_prepare vp;

if (next && (vma != next) && (end == next->vm_end)) {
- remove_next = true;
- if (next->anon_vma && !vma->anon_vma) {
- int error;
+ int ret;

- vma->anon_vma = next->anon_vma;
- error = anon_vma_clone(vma, next);
- if (error)
- return error;
- }
+ remove_next = true;
+ ret = dup_anon_vma(vma, next);
+ if (ret)
+ return ret;
}

init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
@@ -742,10 +762,11 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
struct file *file = vma->vm_file;
bool vma_changed = false;
long adjust_next = 0;
- struct vm_area_struct *exporter = NULL, *importer = NULL;
struct vma_prepare vma_prep;

if (next) {
+ int error = 0;
+
if (end >= next->vm_end) {
/*
* vma expands, overlapping all the next, and
@@ -780,15 +801,14 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
end != remove2->vm_end);
}

- exporter = next;
- importer = vma;
-
/*
* If next doesn't have anon_vma, import from vma after
* next, if the vma overlaps with it.
*/
- if (remove2 != NULL && !next->anon_vma)
- exporter = remove2;
+ if (remove != NULL && !next->anon_vma)
+ error = dup_anon_vma(vma, remove2);
+ else
+ error = dup_anon_vma(vma, remove);

} else if (end > next->vm_start) {
/*
@@ -796,9 +816,8 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
* mprotect case 5 shifting the boundary up.
*/
adjust_next = (end - next->vm_start);
- exporter = next;
- importer = vma;
- VM_WARN_ON(expand != importer);
+ VM_WARN_ON(expand != vma);
+ error = dup_anon_vma(vma, next);
} else if (end < vma->vm_end) {
/*
* vma shrinks, and !insert tells it's not
@@ -806,24 +825,11 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
* mprotect case 4 shifting the boundary down.
*/
adjust_next = -(vma->vm_end - end);
- exporter = vma;
- importer = next;
- VM_WARN_ON(expand != importer);
- }
-
- /*
- * Easily overlooked: when mprotect shifts the boundary,
- * make sure the expanding vma has anon_vma set if the
- * shrinking vma had, to cover any anon pages imported.
- */
- if (exporter && exporter->anon_vma && !importer->anon_vma) {
- int error;
-
- importer->anon_vma = exporter->anon_vma;
- error = anon_vma_clone(importer, exporter);
- if (error)
- return error;
+ VM_WARN_ON(expand != next);
+ error = dup_anon_vma(next, vma);
}
+ if (error)
+ return error;
}

if (vma_iter_prealloc(vmi, vma))
--
2.35.1