The patch titled
Subject: hugetlbfs: add swap entry check in follow_hugetlb_page()
has been added to the -mm tree. Its filename is
hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page.patch
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------------------------------------------------------
From: Naoya Horiguchi <[email protected]>
Subject: hugetlbfs: add swap entry check in follow_hugetlb_page()
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.
The expected behavior is like this:
absent is_swap_pte FOLL_DUMP Expected behavior
-------------------------------------------------------------------
true false false hugetlb_fault
false true false hugetlb_fault
false false false return page
true false true skip page (to avoid allocation)
false true true hugetlb_fault
false false true return page
With this patch, we can call hugetlb_fault() and take proper actions (we
wait for migration entries, fail with VM_FAULT_HWPOISON_LARGE for
hwpoisoned entries,) and as the result we can dump all hugepages except
for hwpoisoned ones.
Signed-off-by: Naoya Horiguchi <[email protected]>
Cc: Rik van Riel <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: HATAYAMA Daisuke <[email protected]>
Acked-by: KOSAKI Motohiro <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: <[email protected]> [2.6.34+?]
Signed-off-by: Andrew Morton <[email protected]>
---
mm/hugetlb.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff -puN mm/hugetlb.c~hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page
mm/hugetlb.c
--- a/mm/hugetlb.c~hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page
+++ a/mm/hugetlb.c
@@ -2961,7 +2961,17 @@ long follow_hugetlb_page(struct mm_struc
break;
}
- if (absent ||
+ /*
+ * We need call hugetlb_fault for both hugepages under migration
+ * (in which case hugetlb_fault waits for the migration,) and
+ * hwpoisoned hugepages (in which case we need to prevent the
+ * caller from accessing to them.) In order to do this, we use
+ * here is_swap_pte instead of is_hugetlb_entry_migration and
+ * is_hugetlb_entry_hwpoisoned. This is because it simply covers
+ * both cases, and because we can't follow correct pages
+ * directly from any kind of swap entries.
+ */
+ if (absent || is_swap_pte(huge_ptep_get(pte)) ||
((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) {
int ret;
_
Patches currently in -mm which might be from [email protected] are
hugetlbfs-stop-setting-vm_dontdump-in-initializing-vmavm_hugetlb.patch
fix-hugetlb-memory-check-in-vma_dump_size.patch
hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page.patch
hwpoison-check-dirty-flag-to-match-against-clean-page.patch
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