[PATCH v3 44/48] mm/mmap: Don't use __vma_adjust() in shift_arg_pages()

[Liam Howlett <liam.howlett@oracle.com>]

From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

Introduce shrink_vma() which uses the vma_prepare() and vma_complete()
functions to reduce the vma coverage.

Convert shift_arg_pages() to use expand_vma() and the new shrink_vma()
function.  Remove support from __vma_adjust() to reduce a vma size since
shift_arg_pages() is the only user that shrinks a VMA in this way.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 fs/exec.c          |  4 ++--
 include/linux/mm.h | 13 ++++------
 mm/mmap.c          | 59 ++++++++++++++++++++++++++++++++++++----------
 3 files changed, 53 insertions(+), 23 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d52fca2dd30b..c0df813d2b45 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -699,7 +699,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
 	/*
 	 * cover the whole range: [new_start, old_end)
 	 */
-	if (vma_adjust(&vmi, vma, new_start, old_end, vma->vm_pgoff))
+	if (vma_expand(&vmi, vma, new_start, old_end, vma->vm_pgoff, NULL))
 		return -ENOMEM;
 
 	/*
@@ -733,7 +733,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
 
 	vma_prev(&vmi);
 	/* Shrink the vma to just the new range */
-	return vma_adjust(&vmi, vma, new_start, new_end, vma->vm_pgoff);
+	return vma_shrink(&vmi, vma, new_start, new_end, vma->vm_pgoff);
 }
 
 /*
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a00871cc63cc..0b229ddf43a4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2822,14 +2822,11 @@ void anon_vma_interval_tree_verify(struct anon_vma_chain *node);
 
 /* mmap.c */
 extern int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin);
-extern int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma, unsigned long start,
-	unsigned long end, pgoff_t pgoff, struct vm_area_struct *expand);
-static inline int vma_adjust(struct vma_iterator *vmi,
-	struct vm_area_struct *vma, unsigned long start, unsigned long end,
-	pgoff_t pgoff)
-{
-	return __vma_adjust(vmi, vma, start, end, pgoff, NULL);
-}
+extern int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		      unsigned long start, unsigned long end, pgoff_t pgoff,
+		      struct vm_area_struct *next);
+extern int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		       unsigned long start, unsigned long end, pgoff_t pgoff);
 extern struct vm_area_struct *vma_merge(struct vma_iterator *vmi,
 	struct mm_struct *, struct vm_area_struct *prev, unsigned long addr,
 	unsigned long end, unsigned long vm_flags, struct anon_vma *,
diff --git a/mm/mmap.c b/mm/mmap.c
index a8c941e3be84..a6e07edc15e9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -637,10 +637,9 @@ static inline void vma_complete(struct vma_prepare *vp,
  *
  * Returns: 0 on success
  */
-inline int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
-		      unsigned long start, unsigned long end, pgoff_t pgoff,
-		      struct vm_area_struct *next)
-
+int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
+	       unsigned long start, unsigned long end, pgoff_t pgoff,
+	       struct vm_area_struct *next)
 {
 	bool remove_next = false;
 	struct vma_prepare vp;
@@ -686,6 +685,44 @@ inline int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 nomem:
 	return -ENOMEM;
 }
+
+/*
+ * vma_shrink() - Reduce an existing VMAs memory area
+ * @vmi: The vma iterator
+ * @vma: The VMA to modify
+ * @start: The new start
+ * @end: The new end
+ *
+ * Returns: 0 on success, -ENOMEM otherwise
+ */
+int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
+	       unsigned long start, unsigned long end, pgoff_t pgoff)
+{
+	struct vma_prepare vp;
+
+	WARN_ON((vma->vm_start != start) && (vma->vm_end != end));
+
+	if (vma_iter_prealloc(vmi, vma))
+		return -ENOMEM;
+
+	init_vma_prep(&vp, vma);
+	vma_adjust_trans_huge(vma, start, end, 0);
+	vma_prepare(&vp);
+
+	if (vma->vm_start < start)
+		vma_iter_clear(vmi, vma->vm_start, start);
+
+	if (vma->vm_end > end)
+		vma_iter_clear(vmi, end, vma->vm_end);
+
+	vma->vm_start = start;
+	vma->vm_end = end;
+	vma->vm_pgoff = pgoff;
+	vma_complete(&vp, vmi, vma->vm_mm);
+	validate_mm(vma->vm_mm);
+	return 0;
+}
+
 /*
  * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
  * is already present in an i_mmap tree without adjusting the tree.
@@ -801,14 +838,7 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
 
 	vma_prepare(&vma_prep);
 
-	if (vma->vm_start < start)
-		vma_iter_clear(vmi, vma->vm_start, start);
-	else if (start != vma->vm_start)
-		vma_changed = true;
-
-	if (vma->vm_end > end)
-		vma_iter_clear(vmi, end, vma->vm_end);
-	else if (end != vma->vm_end)
+	if (start < vma->vm_start || end > vma->vm_end)
 		vma_changed = true;
 
 	vma->vm_start = start;
@@ -821,7 +851,10 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (adjust_next) {
 		next->vm_start += adjust_next;
 		next->vm_pgoff += adjust_next >> PAGE_SHIFT;
-		vma_iter_store(vmi, next);
+		if (adjust_next < 0) {
+			WARN_ON_ONCE(vma_changed);
+			vma_iter_store(vmi, next);
+		}
 	}
 
 	vma_complete(&vma_prep, vmi, mm);
-- 
2.35.1