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    SubjectRe: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or expanding it
    Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

    * Suren Baghdasaryan <surenb@google.com> [230216 00:18]:
    > 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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