From: Michal Hocko <mhocko@xxxxxxxx> Subject: mm, hugetlb: fix huge_pte_alloc BUG_ON Zhong Jiang has reported a BUG_ON from huge_pte_alloc hitting when he runs his database load with memory online and offline running in parallel. The reason is that huge_pmd_share might detect a shared pmd which is currently migrated and so it has migration pte which is !pte_huge. There doesn't seem to be any easy way to prevent from the race and in fact seeing the migration swap entry is not harmful. Both callers of huge_pte_alloc are prepared to handle them. copy_hugetlb_page_range will copy the swap entry and make it COW if needed. hugetlb_fault will back off and so the page fault is retries if the page is still under migration and waits for its completion in hugetlb_fault. That means that the BUG_ON is wrong and we should update it. Let's simply check that all present ptes are pte_huge instead. Link: http://lkml.kernel.org/r/20160721074340.GA26398@xxxxxxxxxxxxxx Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Reported-by: zhongjiang <zhongjiang@xxxxxxxxxx> Acked-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/hugetlb.c~mm-hugetlb-fix-huge_pte_alloc-bug_on mm/hugetlb.c --- a/mm/hugetlb.c~mm-hugetlb-fix-huge_pte_alloc-bug_on +++ a/mm/hugetlb.c @@ -4310,7 +4310,7 @@ pte_t *huge_pte_alloc(struct mm_struct * pte = (pte_t *)pmd_alloc(mm, pud, addr); } } - BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte)); + BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte)); return pte; } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
