The patch titled
Subject: mm: do not use page_count() without a page pin
has been added to the -mm tree. Its filename is
mm-do-not-use-page_count-without-a-page-pin.patch
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From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: mm: do not use page_count() without a page pin
d179e84ba ("mm: vmscan: do not use page_count without a page pin") fixed
this problem in vmscan.c but same problem is in __count_immobile_pages().
I copy and paste d179e84ba's contents for description.
"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."
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Wanpeng Li <liwp.linux@xxxxxxxxx>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff -puN mm/page_alloc.c~mm-do-not-use-page_count-without-a-page-pin mm/page_alloc.c
--- a/mm/page_alloc.c~mm-do-not-use-page_count-without-a-page-pin
+++ a/mm/page_alloc.c
@@ -5499,11 +5499,18 @@ __count_immobile_pages(struct zone *zone
continue;
page = pfn_to_page(check);
- if (!page_count(page)) {
+ /*
+ * We can't use page_count without pin a page
+ * because another CPU can free compound page.
+ * This check already skips compound tails of THP
+ * because their page->_count is zero at all time.
+ */
+ if (!atomic_read(&page->_count)) {
if (PageBuddy(page))
iter += (1 << page_order(page)) - 1;
continue;
}
+
if (!PageLRU(page))
found++;
/*
_
Subject: Subject: mm: do not use page_count() without a page pin
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
linux-next.patch
memory-hotplug-fix-invalid-memory-access-caused-by-stale-kswapd-pointer.patch
memory-hotplug-fix-invalid-memory-access-caused-by-stale-kswapd-pointer-fix.patch
mm-thp-abort-compaction-if-migration-page-cannot-be-charged-to-memcg.patch
swap-allow-swap-readahead-to-be-merged.patch
documentation-update-how-page-cluster-affects-swap-i-o.patch
mm-compaction-cleanup-on-compaction_deferred.patch
memcg-prevent-oom-with-too-many-dirty-pages.patch
mm-clear-pages_scanned-only-if-draining-a-pcp-adds-pages-to-the-buddy-allocator-again.patch
mm-fix-page-reclaim-comment-error.patch
mm-do-not-use-page_count-without-a-page-pin.patch
mm-clean-up-__count_immobile_pages.patch
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