[PATCH] hugetlbfs: Call VM_BUG_ON_PAGE earlier in free_huge_page

[Yongkai Wu]

A stack trace was triggered by VM_BUG_ON_PAGE(page_mapcount(page),
page) in free_huge_page().  Unfortunately, the page->mapping field
was set to NULL before this test.  This made it more difficult to
determine the root cause of the problem.

Move the VM_BUG_ON_PAGE tests earlier in the function so that if
they do trigger more information is present in the page struct.

Signed-off-by: Yongkai Wu <ni...@163.com>
Acked-by: Michal Hocko <mho...@suse.com>
Acked-by: Mike Kravetz <mike.krav...@oracle.com>
---
 mm/hugetlb.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7f2a28a..14ef274 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1248,10 +1248,11 @@ void free_huge_page(struct page *page)
                (struct hugepage_subpool *)page_private(page);
        bool restore_reserve;
 
-       set_page_private(page, 0);
-       page->mapping = NULL;
        VM_BUG_ON_PAGE(page_count(page), page);
        VM_BUG_ON_PAGE(page_mapcount(page), page);
+
+       set_page_private(page, 0);
+       page->mapping = NULL;
        restore_reserve = PagePrivate(page);
        ClearPagePrivate(page);
 
-- 
1.8.3.1