(4/3/13 2:35 PM), Naoya Horiguchi wrote: > 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)); Hmmm... Now absent has two meanings. 1) skip hugetlb_fault() and return immediately if FOLL_DUMP is used. 2) call hugetlb_fault() if to be need page population or cow. The description of this patch only explain about (2). and I'm not convinced why we don't need to dump pages under migraion. -- 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>