[PATCH v5.1 10/19] mm/mmap: Support vma == NULL in init_vma_munmap()

[Bert Karwatzki <spasswolf@web.de>]

Adding support for a NULL vma means the init_vma_munmap() can be
initialized for a less error-prone process when calling
vms_complete_munmap_vmas() later on.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mmap.c |  5 +----
 mm/vma.c  | 26 ++++++++++++++++----------
 mm/vma.h  | 14 ++++++++++++++
 3 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 56d0aaff8478..16fd14b243f9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1395,16 +1395,13 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	if (unlikely(!can_modify_mm(mm, addr, end)))
 		return -EPERM;

-	 /* arch_unmap() might do unmaps itself.  */
-	arch_unmap(mm, addr, end);
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
+	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 	if (vma) {
 		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
 		mt_on_stack(mt_detach);
 		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
-		init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 		/* Prepare to unmap any existing mapping in the area */
 		if (vms_gather_munmap_vmas(&vms, &mas_detach))
 			return -ENOMEM;
diff --git a/mm/vma.c b/mm/vma.c
index e4677364082b..a5ca42b7161b 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -352,16 +352,22 @@ static void __vma_link_file(struct vm_area_struct *vma,
  * @uf: The userfaultfd list_head
  * @unlock: Unlock after the operation.  Only unlocked on success
  */
-static inline void init_vma_munmap(struct vma_munmap_struct *vms,
+void
+init_vma_munmap(struct vma_munmap_struct *vms,
 		struct vma_iterator *vmi, struct vm_area_struct *vma,
-		unsigned long start, unsigned long end, struct list_head *uf,
-		bool unlock)
+		unsigned long start, unsigned long end,
+		struct list_head *uf, bool unlock)
 {
 	vms->vmi = vmi;
 	vms->vma = vma;
-	vms->mm = vma->vm_mm;
-	vms->start = start;
-	vms->end = end;
+	if (vma) {
+		vms->mm = vma->vm_mm;
+		vms->start = start;
+		vms->end = end;
+	} else {
+		vms->mm = NULL;
+		vms->start = vms->end = 0;
+	}
 	vms->unlock = unlock;
 	vms->uf = uf;
 	vms->vma_count = 0;
@@ -699,8 +705,8 @@ static inline void abort_munmap_vmas(struct ma_state *mas_detach)
  * needed to be done once the vma maple tree is updated.
  */

-static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
-		struct ma_state *mas_detach)
+void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
+			      struct ma_state *mas_detach)
 {
 	struct vm_area_struct *vma;
 	struct mm_struct *mm;
@@ -748,8 +754,8 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
  *
  * Return: 0 on success
  */
-static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
-		struct ma_state *mas_detach)
+int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
+			   struct ma_state *mas_detach)
 {
 	struct vm_area_struct *next = NULL;
 	int error = -ENOMEM;
diff --git a/mm/vma.h b/mm/vma.h
index 7ba0d71b50ca..8b2401f93c74 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -63,6 +63,12 @@ void anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma);
 /* Required for do_brk_flags(). */
 void vma_prepare(struct vma_prepare *vp);

+/* Required for mmap_region() */
+void init_vma_munmap(struct vma_munmap_struct *vms,
+		     struct vma_iterator *vmi, struct vm_area_struct *vma,
+		     unsigned long start, unsigned long end,
+		     struct list_head *uf, bool unlock);
+
 /* Required for do_brk_flags(). */
 void init_vma_prep(struct vma_prepare *vp,
 		   struct vm_area_struct *vma);
@@ -78,6 +84,14 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	       unsigned long start, unsigned long end, pgoff_t pgoff);

+/* Required for mmap_region() */
+void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
+			      struct ma_state *mas_detach);
+
+/* Required for mmap_region() */
+int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
+			   struct ma_state *mas_detach);
+
 int
 do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		    struct mm_struct *mm, unsigned long start,
--
2.45.2