From 70524269062e7431127027334739c297a7ce7bc1 Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@suse.com> Date: Tue, 2 Aug 2016 14:02:34 -0700 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. Link: http://lkml.kernel.org/r/20160721074340.GA26398@dhcp22.suse.cz Signed-off-by: Michal Hocko <mhocko@suse.com> Reported-by: zhongjiang <zhongjiang@huawei.com> Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 619e00d82c5d8..ef968306fd5b8 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4310,7 +4310,7 @@ 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; } -- 2.39.5