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Message-ID: <799d6831-2af3-72c1-84b2-1f0454a46c07@redhat.com>
Date: Thu, 8 Dec 2022 14:16:03 +0100
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: Jann Horn <jannh@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>,
James Houghton <jthoughton@...gle.com>,
Rik van Riel <riel@...riel.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Nadav Amit <nadav.amit@...il.com>,
John Hubbard <jhubbard@...dia.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk()
is safe to walk
On 07.12.22 21:31, Peter Xu wrote:
> Taking vma lock here is not needed for now because all potential hugetlb
> walkers here should have i_mmap_rwsem held. Document the fact.
>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
> mm/page_vma_mapped.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index e97b2e23bd28..2e59a0419d22 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -168,8 +168,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> /* The only possible mapping was handled on last iteration */
> if (pvmw->pte)
> return not_found(pvmw);
> -
> - /* when pud is not present, pte will be NULL */
> + /*
> + * NOTE: we don't need explicit lock here to walk the
> + * hugetlb pgtable because either (1) potential callers of
> + * hugetlb pvmw currently holds i_mmap_rwsem, or (2) the
> + * caller will not walk a hugetlb vma (e.g. ksm or uprobe).
> + * When one day this rule breaks, one will get a warning
> + * in hugetlb_walk(), and then we'll figure out what to do.
> + */
> pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
> if (!pvmw->pte)
> return false;
Would it make sense to squash that into the previous commit?
--
Thanks,
David / dhildenb
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