We have further discussed the patch and I believe it is not correct. See [1]. I am proposing the following alternative. [1] http://lkml.kernel.org/r/20160720132431.GM11249@xxxxxxxxxxxxxx --- >From b1e9b3214f1859fdf7d134cdcb56f5871933539c Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxxx> Date: Thu, 21 Jul 2016 09:28:13 +0200 Subject: [PATCH] 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. Reported-by: zhongjiang <zhongjiang@xxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 34379d653aa3..31dd2b8b86b3 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4303,7 +4303,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, 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; } -- 2.8.1 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>