在 2020/2/22 13:23, Qian Cai 写道:
On Feb 21, 2020, at 10:34 PM, Longpeng(Mike) longpeng2@huawei.com wrote:
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dd8737a..90daf37 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4910,28 +4910,30 @@ pte_t *huge_pte_offset(struct mm_struct *mm, { pgd_t *pgd; p4d_t *p4d;
- pud_t *pud;
- pmd_t *pmd;
pud_t *pud, pud_entry;
pmd_t *pmd, pmd_entry;
pgd = pgd_offset(mm, addr);
- if (!pgd_present(*pgd))
- if (!pgd_present(READ_ONCE(*pgd))) return NULL; p4d = p4d_offset(pgd, addr);
- if (!p4d_present(*p4d))
- if (!p4d_present(READ_ONCE(*p4d))) return NULL;
What’s the point of READ_ONCE() on those two places?
As explained in the commit messages, it's for safe(e.g. avoid the compilier mischief). You can also find the same usage in the ARM64's huge_pte_offset() in arch/arm64/mm/hugetlbpage.c