Re: [PATCH v2 07/10] mm/hugetlb: Make follow_hugetlb_page() safe to pmd unshare

John Hubbard
2022-12-07T23:27:04Z

On 12/7/22 12:30, Peter Xu wrote:
> Since follow_hugetlb_page() walks the pgtable, it needs the vma lock
> to make sure the pgtable page will not be freed concurrently.
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/hugetlb.c | 7 +++++++
> 1 file changed, 7 insertions(+)

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
--
John Hubbard
NVIDIA

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3fbbd599d015..f42399522805 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6284,6 +6284,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> break;
> }
>
> + hugetlb_vma_lock_read(vma);
> /*
> * Some archs (sparc64, sh*) have multiple pte_ts to
> * each hugepage. We have to make sure we get the
> @@ -6308,6 +6309,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> !hugetlbfs_pagecache_present(h, vma, vaddr)) {
> if (pte)
> spin_unlock(ptl);
> + hugetlb_vma_unlock_read(vma);
> remainder = 0;
> break;
> }
> @@ -6329,6 +6331,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>
> if (pte)
> spin_unlock(ptl);
> + hugetlb_vma_unlock_read(vma);
> +
> if (flags & FOLL_WRITE)
> fault_flags |= FAULT_FLAG_WRITE;
> else if (unshare)
> @@ -6388,6 +6392,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> remainder -= pages_per_huge_page(h);
> i += pages_per_huge_page(h);
> spin_unlock(ptl);
> + hugetlb_vma_unlock_read(vma);
> continue;
> }
>
> @@ -6415,6 +6420,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> if (WARN_ON_ONCE(!try_grab_folio(pages[i], refs,
> flags))) {
> spin_unlock(ptl);
> + hugetlb_vma_unlock_read(vma);
> remainder = 0;
> err = -ENOMEM;
> break;
> @@ -6426,6 +6432,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> i += refs;
>
> spin_unlock(ptl);
> + hugetlb_vma_unlock_read(vma);
> }
> *nr_pages = remainder;
> /*