The patch titled
Subject: mm: do not use page_count() without a page pin
has been removed from the -mm tree. Its filename was
mm-do-not-use-page_count-without-a-page-pin.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
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
@@ -5500,11 +5500,18 @@ __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++;
/*
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
origin.patch
mm-remove-__gfp_no_kswapd.patch
remove-__gfp_no_kswapd-fixes-fix.patch
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