Commit bf6bddf1924e ("mm: introduce compaction and migration for ballooned
pages") introduces page_count(page) into memory compaction which
dereferences page->first_page if PageTail(page).
Introduce a store memory barrier to ensure page->first_page is properly
initialized so that code that does page_count(page) on pages off the lru
always have a valid p->first_page.
Reported-by: Holger Kiehl <Holger.Kiehl@xxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
v2: with commentary, per checkpatch
mm/page_alloc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -369,9 +369,11 @@ void prep_compound_page(struct page *page, unsigned long order)
__SetPageHead(page);
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;
- __SetPageTail(p);
set_page_count(p, 0);
p->first_page = page;
+ /* Make sure p->first_page is always valid for PageTail() */
+ smp_wmb();
+ __SetPageTail(p);
}
}
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