hugetlb: fix __prep_compound_gigantic_page page flag setting

Commit 2b21624fc232 ("hugetlb: freeze allocated pages before creating
hugetlb pages") changed the order page flags were cleared and set in the
head page.  It moved the __ClearPageReserved after __SetPageHead.
However, there is a check to make sure __ClearPageReserved is never done
on a head page.  If CONFIG_DEBUG_VM_PGFLAGS is enabled, the following BUG
will be hit when creating a hugetlb gigantic page:

    page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
    ------------[ cut here ]------------
    kernel BUG at include/linux/page-flags.h:500!
    Call Trace will differ depending on whether hugetlb page is created
    at boot time or run time.

Make sure to __ClearPageReserved BEFORE __SetPageHead.

Link: https://lkml.kernel.org/r/20221118195249.178319-1-mike.kravetz@oracle.com
Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Acked-by: Muchun Song <songmuchun@bytedance.com>
Tested-by: Tarun Sahu <tsahu@linux.ibm.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e48f8ef45b17ff9cfd225815ad599345dcbf5491..f1385c3b6c9638119c29fd240a8fb501d7f9ba13 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1800,6 +1800,7 @@ static bool __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);
+       __ClearPageReserved(page);
        __SetPageHead(page);
        for (i = 0; i < nr_pages; i++) {
                p = nth_page(page, i);
@@ -1816,7 +1817,8 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
                 * on the head page when they need know if put_page() is needed
                 * after get_user_pages().
                 */
-               __ClearPageReserved(p);
+               if (i != 0)     /* head page cleared above */
+                       __ClearPageReserved(p);
                /*
                 * Subtle and very unlikely
                 *