From 20156ce2365d61beaa6f5a78a7a789044e0e7acc Mon Sep 17 00:00:00 2001 From: Huang Shijie Date: Tue, 8 Nov 2016 13:44:38 +0800 Subject: [PATCH] arm64: hugetlb: remove the wrong pmd check in find_num_contig() The find_num_contig() will return 1 when the pmd is not present. It will cause a kernel dead loop in the following scenaro: 1.) pmd entry is not present. 2.) the page fault occurs: ... hugetlb_fault() --> hugetlb_no_page() --> set_huge_pte_at() 3.) set_huge_pte_at() will only set the first PMD entry, since the find_num_contig just return 1 in this case. So the PMD entries are all empty except the first one. 4.) when kernel accesses the address mapped by the second PMD entry, a new page fault occurs: ... hugetlb_fault() --> huge_ptep_set_access_flags() The second PMD entry is still empty now. 5.) When the kernel returns, the access will cause a page fault again. The kernel will run like the "4)" above. We will see a dead loop since here. The dead loop is caught in the 32M hugetlb page (2M PMD + Contiguous bit). This patch removes wrong pmd check, and fixes this dead loop. This patch also removes the redundant checks for PGD/PUD in the find_num_contig(). Acked-by: Steve Capper Signed-off-by: Huang Shijie Reviewed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- arch/arm64/mm/hugetlbpage.c | 12 ------------ 1 file changed, 12 deletions(-) diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 0a4c97b..9a1069d 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -51,20 +51,8 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr, *pgsize = PAGE_SIZE; if (!pte_cont(pte)) return 1; - if (!pgd_present(*pgd)) { - VM_BUG_ON(!pgd_present(*pgd)); - return 1; - } pud = pud_offset(pgd, addr); - if (!pud_present(*pud)) { - VM_BUG_ON(!pud_present(*pud)); - return 1; - } pmd = pmd_offset(pud, addr); - if (!pmd_present(*pmd)) { - VM_BUG_ON(!pmd_present(*pmd)); - return 1; - } if ((pte_t *)pmd == ptep) { *pgsize = PMD_SIZE; return CONT_PMDS; -- 2.7.4