From dd361e5033cf36c51acab996ea17748b81cedb38 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Fri, 16 Dec 2022 10:52:26 -0500 Subject: mm/hugetlb: make walk_hugetlb_range() safe to pmd unshare Since walk_hugetlb_range() walks the pgtable, it needs the vma lock to make sure the pgtable page will not be freed concurrently. Link: https://lkml.kernel.org/r/20221216155226.2043738-1-peterx@redhat.com Signed-off-by: Peter Xu Reviewed-by: Mike Kravetz Reviewed-by: John Hubbard Cc: Andrea Arcangeli Cc: David Hildenbrand Cc: James Houghton Cc: Jann Horn Cc: Miaohe Lin Cc: Muchun Song Cc: Nadav Amit Cc: Rik van Riel Signed-off-by: Andrew Morton --- mm/hmm.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'mm/hmm.c') diff --git a/mm/hmm.c b/mm/hmm.c index 601a99ce3c84..6a151c09de5e 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -492,8 +492,21 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask, required_fault = hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags); if (required_fault) { + int ret; + spin_unlock(ptl); - return hmm_vma_fault(addr, end, required_fault, walk); + hugetlb_vma_unlock_read(vma); + /* + * Avoid deadlock: drop the vma lock before calling + * hmm_vma_fault(), which will itself potentially take and + * drop the vma lock. This is also correct from a + * protection point of view, because there is no further + * use here of either pte or ptl after dropping the vma + * lock. + */ + ret = hmm_vma_fault(addr, end, required_fault, walk); + hugetlb_vma_lock_read(vma); + return ret; } pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT); -- cgit v1.2.3