[PATCH] nommu page refcount bug fixing

[Luke Yang]

Hi all,

   The previous "nommu use compound pages" patch has a problem: when
the pages allocated is not compound page (eg: slab allocator), the
refcount value of every page still need to be set, otherwise the
get/put_page() would free a single page improperly, such as in
access_process_vm().

Signed-off-by: Luke Yang <luke.adi@xxxxxxxxx>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b7f14a4..fc8b544 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -436,6 +436,14 @@ static void __free_pages_ok(struct page
                mutex_debug_check_no_locks_freed(page_address(page),
                                                 PAGE_SIZE<<order);

+#ifndef CONFIG_MMU
+       if (!PageCompound(page)) {
+               for (i = 1 ; i < (1 << order) ; ++i) {
+                       __put_page(page + i);
+               }
+       }
+#endif
+
        for (i = 0 ; i < (1 << order) ; ++i)
                reserved += free_pages_check(page + i);
        if (reserved)
@@ -453,6 +461,8 @@ static void __free_pages_ok(struct page
  */
 void fastcall __init __free_pages_bootmem(struct page *page, unsigned
int order)
 {
+       int i;
+
        if (order == 0) {
                __ClearPageReserved(page);
                set_page_count(page, 0);
@@ -472,6 +482,11 @@ void fastcall __init __free_pages_bootme
                }

                set_page_refcounted(page);
+
+#ifndef CONFIG_MMU
+               for (i = 1; i < (1 << order); i++)
+                       set_page_refcounted(page + i);
+#endif
                __free_pages(page, order);
        }
 }
@@ -512,6 +527,8 @@ static inline void expand(struct zone *z
  */
 static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 {
+       int i;
+
        if (unlikely(page_mapcount(page) |
                (page->mapping != NULL)  |
                (page_count(page) != 0)  |
@@ -539,7 +556,21 @@ static int prep_new_page(struct page *pa
                        1 << PG_referenced | 1 << PG_arch_1 |
                        1 << PG_checked | 1 << PG_mappedtodisk);
        set_page_private(page, 0);
+
        set_page_refcounted(page);
+
+#ifndef CONFIG_MMU
+       if (!(gfp_flags & __GFP_COMP)) {
+               /*
+                * Reference all the pages for this order, otherwise if
+                * anyone accesses one of the pages with (get/put) it
+                * will be freed. - eg: access_process_vm()
+                */
+               for (i = 1; i < (1 << order); i++)
+                       set_page_refcounted(page + i);
+       }
+#endif
+
        kernel_map_pages(page, 1 << order, 1);

        if (gfp_flags & __GFP_ZERO)

--
Best regards,
Luke Yang
luke.adi@xxxxxxxxx
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b7f14a4..fc8b544 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -436,6 +436,14 @@ static void __free_pages_ok(struct page 
 		mutex_debug_check_no_locks_freed(page_address(page),
 						 PAGE_SIZE<<order);
 
+#ifndef CONFIG_MMU
+	if (!PageCompound(page)) {
+		for (i = 1 ; i < (1 << order) ; ++i) {
+			__put_page(page + i);
+		}
+	}
+#endif
+
 	for (i = 0 ; i < (1 << order) ; ++i)
 		reserved += free_pages_check(page + i);
 	if (reserved)
@@ -453,6 +461,8 @@ static void __free_pages_ok(struct page 
  */
 void fastcall __init __free_pages_bootmem(struct page *page, unsigned int order)
 {
+	int i;
+
 	if (order == 0) {
 		__ClearPageReserved(page);
 		set_page_count(page, 0);
@@ -472,6 +482,11 @@ void fastcall __init __free_pages_bootme
 		}
 
 		set_page_refcounted(page);
+
+#ifndef CONFIG_MMU
+		for (i = 1; i < (1 << order); i++)
+			set_page_refcounted(page + i);
+#endif
 		__free_pages(page, order);
 	}
 }
@@ -512,6 +527,8 @@ static inline void expand(struct zone *z
  */
 static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 {
+	int i;
+
 	if (unlikely(page_mapcount(page) |
 		(page->mapping != NULL)  |
 		(page_count(page) != 0)  |
@@ -539,7 +556,21 @@ static int prep_new_page(struct page *pa
 			1 << PG_referenced | 1 << PG_arch_1 |
 			1 << PG_checked | 1 << PG_mappedtodisk);
 	set_page_private(page, 0);
+
 	set_page_refcounted(page);
+
+#ifndef CONFIG_MMU
+	if (!(gfp_flags & __GFP_COMP)) {
+		/*
+		 * Reference all the pages for this order, otherwise if
+		 * anyone accesses one of the pages with (get/put) it
+		 * will be freed. - eg: access_process_vm()
+		 */
+		for (i = 1; i < (1 << order); i++)
+			set_page_refcounted(page + i);
+	}
+#endif
+
 	kernel_map_pages(page, 1 << order, 1);
 
 	if (gfp_flags & __GFP_ZERO)