[PATCH v2 16/33] mm/mmap: write-lock VMA before shrinking or expanding it

[Suren Baghdasaryan]

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 <sur...@google.com>
---
 mm/mmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 6fff76334177..60038c24d836 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