The patch titled
mm: vmscan: do not use page_count without a page pin
has been added to the -mm tree. Its filename is
mm-vmscan-do-not-use-page_count-without-a-page-pin.patch
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------------------------------------------------------
Subject: mm: vmscan: do not use page_count without a page pin
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
It is unsafe to run page_count during the physical pfn scan because
compound_head could trip on a dangling pointer when reading
page->first_page if the compound page is being freed by another CPU.
[mgorman@xxxxxxx: split out patch]
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff -puN mm/vmscan.c~mm-vmscan-do-not-use-page_count-without-a-page-pin mm/vmscan.c
--- a/mm/vmscan.c~mm-vmscan-do-not-use-page_count-without-a-page-pin
+++ a/mm/vmscan.c
@@ -1124,8 +1124,20 @@ static unsigned long isolate_lru_pages(u
nr_lumpy_dirty++;
scan++;
} else {
- /* the page is freed already. */
- if (!page_count(cursor_page))
+ /*
+ * Check if the page is freed already.
+ *
+ * We can't use page_count() as that
+ * requires compound_head and we don't
+ * have a pin on the page here. If a
+ * page is tail, we may or may not
+ * have isolated the head, so assume
+ * it's not free, it'd be tricky to
+ * track the head status without a
+ * page pin.
+ */
+ if (!PageTail(cursor_page) &&
+ !atomic_read(&cursor_page->_count))
continue;
break;
}
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
mm-remove-khugepaged-double-thp-vmstat-update-with-config_numa=n.patch
mm-migratec-dont-account-swapcache-as-shmem.patch
include-asm-generic-pgtableh-fix-unbalanced-parenthesis.patch
mm-fix-negative-commitlimit-when-gigantic-hugepages-are-allocated.patch
memcg-clear-mm-owner-when-last-possible-owner-leaves.patch
mm-memory-failurec-fix-page-isolated-count-mismatch.patch
mm-vmscan-do-not-use-page_count-without-a-page-pin.patch
ksm-fix-null-pointer-dereference-in-scan_get_next_rmap_item.patch
pagewalk-fix-walk_page_range-dont-check-find_vma-result-properly.patch
pagewalk-dont-look-up-vma-if-walk-hugetlb_entry-is-unused.patch
pagewalk-add-locking-rule-comments.patch
pagewalk-add-locking-rule-comments-fix.patch
pagewalk-fix-code-comment-for-thp.patch
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