The patch titled
Subject: mm, hugetlb: fix huge_pte_alloc BUG_ON
has been added to the -mm tree. Its filename is
mm-hugetlb-fix-huge_pte_alloc-bug_on.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-fix-huge_pte_alloc-bug_on.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-fix-huge_pte_alloc-bug_on.patch
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------------------------------------------------------
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;
}
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-hugetlb-fix-huge_pte_alloc-bug_on.patch
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