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. Acked-by: Steve Capper <steve.cap...@arm.com> Signed-off-by: Huang Shijie <shijie.hu...@arm.com> --- arch/arm64/mm/hugetlbpage.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 2e49bd2..4811ef1 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -61,10 +61,6 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr, 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; -- 2.5.5