vma_expand and vma_shrink change VMA boundaries. Expansion might also
result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent
concurrent page faults.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/mmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index ec2f8d0af280..f079e5bbcd57 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		ret = dup_anon_vma(vma, next);
 		if (ret)
 			return ret;
+
+		/* Lock the VMA  before removing it */
+		vma_start_write(next);
 	}
 
 	init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);

@@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (vma_iter_prealloc(vmi))
 		goto nomem;
 
+	vma_start_write(vma);
 	vma_adjust_trans_huge(vma, start, end, 0);
 	/* VMA iterator points to previous, so set to start if necessary */
 	if (vma_iter_addr(vmi) != start)

@@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (vma_iter_prealloc(vmi))
 		return -ENOMEM;
 
+	vma_start_write(vma);
 	init_vma_prep(&vp, vma);
 	vma_adjust_trans_huge(vma, start, end, 0);
 	vma_prepare(&vp);

-- 
2.39.1