On 2016/7/29 19:27, Michal Hocko wrote: > On Thu 21-07-16 09:43:40, Michal Hocko wrote: >> We have further discussed the patch and I believe it is not correct. See [1]. >> I am proposing the following alternative. > Andrew, please drop the mm-hugetlb-fix-race-when-migrate-pages.patch. It > is clearly racy. Whether the BUG_ON update is really the right and > sufficient fix is not 100% clear yet and we are waiting for Zhong Jiang > testing. The issue is very hard to recur. Without attaching any patch to kernel code. up to now, it still not happens to it. Thanks zhongjiang >> [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>