[PATCH] mm/page_alloc: Restrict and formalize compound_page_dtors[]

[Anshuman Khandual]

Restrict elements in compound_page_dtors[] array per NR_COMPOUND_DTORS and
explicitly position them according to enum compound_dtor_id. This improves
protection against possible misalignment between compound_page_dtors[] and
enum compound_dtor_id later on.

Cc: Andrew Morton <a...@linux-foundation.org>
Cc: linux...@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khand...@arm.com>
---
 include/linux/mm.h |  2 +-
 mm/page_alloc.c    | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 688558c57751..d1bd7736a5e5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -856,7 +856,7 @@ enum compound_dtor_id {
 #endif
        NR_COMPOUND_DTORS,
 };
-extern compound_page_dtor * const compound_page_dtors[];
+extern compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS];
 
 static inline void set_compound_page_dtor(struct page *page,
                enum compound_dtor_id compound_dtor)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cef05d3a23f5..2e4c23b34940 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -302,14 +302,14 @@ const char * const migratetype_names[MIGRATE_TYPES] = {
 #endif
 };
 
-compound_page_dtor * const compound_page_dtors[] = {
-       NULL,
-       free_compound_page,
+compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
+       [NULL_COMPOUND_DTOR] = NULL,
+       [COMPOUND_PAGE_DTOR] = free_compound_page,
 #ifdef CONFIG_HUGETLB_PAGE
-       free_huge_page,
+       [HUGETLB_PAGE_DTOR] = free_huge_page,
 #endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-       free_transhuge_page,
+       [TRANSHUGE_PAGE_DTOR] = free_transhuge_page,
 #endif
 };
 
-- 
2.20.1