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Subject[PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or expanding it
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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
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