hugetlb: clear PG_reserved before setting PG_head on gigantic pages

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>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8ee4d8eb1473ff5bb4175e68903e2c733dbc65ed..162b53b22b49a98986e2da9389d17287c887688a 100644 (file)
--- 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