[PATCH] hugetlb: clear PG_reserved before setting PG_head on gigantic pages

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

PF_NO_COMPOUND for PG_reserved assumes we don't use PG_reserved for
compound pages. And we generally don't. But during allocation of
gigantic pages we set PG_head before clearing PG_reserved and
__ClearPageReserved() steps on the VM_BUG_ON_PAGE().

The fix is trivial: set PG_head after PG_reserved.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
---

Andrew, this patch can be folded into "page-flags: define PG_reserved behavior on compound pages".

---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6ecf61ffa65d..bd3f3e20313b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1258,8 +1258,8 @@ static void prep_compound_gigantic_page(struct page *page, unsigned int order)
 
 	/* we rely on prep_new_huge_page to set the destructor */
 	set_compound_order(page, order);
-	__SetPageHead(page);
 	__ClearPageReserved(page);
+	__SetPageHead(page);
 	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
 		/*
 		 * For gigantic hugepages allocated through bootmem at
-- 
2.5.3

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