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SubjectRe: [RFC PATCH RESEND 11/28] mm/mmap: mark VMAs as locked before merging or splitting them
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Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> Decisions about whether VMAs can be merged or split must be made while
> VMAs are protected from the changes which can affect that decision.
> For example, merge_vma uses vma->anon_vma in its decision whether the
> VMA can be merged. Meanwhile, page fault handler changes vma->anon_vma
> during COW operation.
> Mark all VMAs which might be affected by a merge or split operation as
> locked before making decision how such operations should be performed.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> mm/mmap.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index ed58cf0689b2..ade3909c89b4 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1147,10 +1147,17 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
> if (vm_flags & VM_SPECIAL)
> return NULL;
>
> + if (prev)
> + vma_mark_locked(prev);
> next = vma_next(mm, prev);
> area = next;
> - if (area && area->vm_end == end) /* cases 6, 7, 8 */
> + if (area)
> + vma_mark_locked(area);
> + if (area && area->vm_end == end) { /* cases 6, 7, 8 */
> next = next->vm_next;
> + if (next)
> + vma_mark_locked(next);
> + }
>
> /* verify some invariant that must be enforced by the caller */
> VM_WARN_ON(prev && addr <= prev->vm_start);
> @@ -2687,6 +2694,7 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
> struct vm_area_struct *new;
> int err;
>
> + vma_mark_locked(vma);
> if (vma->vm_ops && vma->vm_ops->may_split) {
> err = vma->vm_ops->may_split(vma, addr);
> if (err)

That looks good to me, the new VMA allocated by vm_area_dup(vma) is
inheriting the locked state from vma.

Reviewed-by: Laurent Dufour <laurent.dufour@fr.ibm.com>

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