On 12/7/22 12:31, 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@xxxxxxxxxx> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> --- 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. + */
Confused. Is this documentation actually intended to refer to hugetlb_walk() itself, or just this call site? If the former, then let's move it over to be right before hugetlb_walk().
pvmw->pte = hugetlb_walk(vma, pvmw->address, size); if (!pvmw->pte) return false;
thanks, -- John Hubbard NVIDIA
