thp: put_page: recheck PageHead after releasing the compound_lock
After releasing the compound_lock split_huge_page can still run and release the
page before put_page_testzero runs.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swap.c b/mm/swap.c
index 33f5292..e0eeef9 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -131,8 +131,12 @@
atomic_dec(&page->_count);
VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
compound_unlock_irqrestore(page_head, flags);
- if (put_page_testzero(page_head))
- __put_compound_page(page_head);
+ if (put_page_testzero(page_head)) {
+ if (PageHead(page_head))
+ __put_compound_page(page_head);
+ else
+ __put_single_page(page_head);
+ }
} else {
/* page_head is a dangling pointer */
VM_BUG_ON(PageTail(page));
