With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory error happens on a hugepage and the affected processes try to access the error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) in get_page(). The reason for this bug is that coredump-related code doesn't recognise "hugepage hwpoison entry" with which a pmd entry is replaced when a memory error occurs on a hugepage. In other words, physical address information is stored in different bit layout between hugepage hwpoison entry and pmd entry, so follow_hugetlb_page() which is called in get_dump_page() returns a wrong page from a given address. We need to filter out only hwpoison hugepages to have data on healthy hugepages in coredump. So this patch makes follow_hugetlb_page() avoid trying to get page when a pmd is in swap entry like format. ChangeLog v3: - add comment about using is_swap_pte() Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Reviewed-by: Michal Hocko <mhocko@xxxxxxx> Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- mm/hugetlb.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git v3.9-rc3.orig/mm/hugetlb.c v3.9-rc3/mm/hugetlb.c index 0d1705b..3bc20bd 100644 --- v3.9-rc3.orig/mm/hugetlb.c +++ v3.9-rc3/mm/hugetlb.c @@ -2966,9 +2966,15 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, * Some archs (sparc64, sh*) have multiple pte_ts to * each hugepage. We have to make sure we get the * first, for the page indexing below to work. + * + * is_swap_pte test covers both is_hugetlb_entry_hwpoisoned + * and hugepages under migration in which case + * hugetlb_fault waits for the migration and bails out + * properly for HWPosined pages. */ pte = huge_pte_offset(mm, vaddr & huge_page_mask(h)); - absent = !pte || huge_pte_none(huge_ptep_get(pte)); + absent = !pte || huge_pte_none(huge_ptep_get(pte)) || + is_swap_pte(huge_ptep_get(pte)); /* * When coredumping, it suits get_dump_page if we just return -- 1.7.11.7 -- 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>