[PATCH] remove set_page_count() outside mm/

set_page_count usage outside mm/ is limited to setting the refcount to 1.
Remove set_page_count from outside mm/, and replace those users with
init_page_count() and set_page_refcounted().

This allows more debug checking, and tighter control on how code is allowed
to play around with page->_count.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 21 insertions, 11 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 39d49ec..20117a4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -18,6 +18,7 @@
 #include <asm/pgtable.h>
 
 #include <linux/hugetlb.h>
+#include "internal.h"
 
 const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
 static unsigned long nr_huge_pages, free_huge_pages;
@@ -106,7 +107,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma, unsigned long addr)
 		return NULL;
 	}
 	spin_unlock(&hugetlb_lock);
-	set_page_count(page, 1);
+	set_page_refcounted(page);
 	for (i = 0; i < (HPAGE_SIZE/PAGE_SIZE); ++i)
 		clear_user_highpage(&page[i], addr);
 	return page;
@@ -152,7 +153,7 @@ static void update_and_free_page(struct page *page)
 				1 << PG_private | 1<< PG_writeback);
 	}
 	page[1].lru.next = NULL;
-	set_page_count(page, 1);
+	set_page_refcounted(page);
 	__free_pages(page, HUGETLB_PAGE_ORDER);
 }
 
diff --git a/mm/internal.h b/mm/internal.h
index 7bb3397..d20e3cc 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -13,8 +13,19 @@
 
 #include <linux/mm.h>
 
-static inline void set_page_refs(struct page *page, int order)
+static inline void set_page_count(struct page *page, int v)
 {
+	atomic_set(&page->_count, v);
+}
+
+/*
+ * Turn a non-refcounted page (->_count == 0) into refcounted with
+ * a count of one.
+ */
+static inline void set_page_refcounted(struct page *page)
+{
+	BUG_ON(PageCompound(page) && page_private(page) != (unsigned long)page);
+	BUG_ON(atomic_read(&page->_count));
 	set_page_count(page, 1);
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e197818..7f65b5a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -442,7 +442,7 @@ void fastcall __init __free_pages_bootmem(struct page *page, unsigned int order)
 	if (order == 0) {
 		__ClearPageReserved(page);
 		set_page_count(page, 0);
-		set_page_refs(page, 0);
+		set_page_refcounted(page);
 		__free_page(page);
 	} else {
 		int loop;
@@ -457,7 +457,7 @@ void fastcall __init __free_pages_bootmem(struct page *page, unsigned int order)
 			set_page_count(p, 0);
 		}
 
-		set_page_refs(page, order);
+		set_page_refcounted(page);
 		__free_pages(page, order);
 	}
 }
@@ -525,7 +525,7 @@ static int prep_new_page(struct page *page, int order)
 			1 << PG_referenced | 1 << PG_arch_1 |
 			1 << PG_checked | 1 << PG_mappedtodisk);
 	set_page_private(page, 0);
-	set_page_refs(page, order);
+	set_page_refcounted(page);
 	kernel_map_pages(page, 1 << order, 1);
 	return 0;
 }
@@ -755,10 +755,8 @@ void split_page(struct page *page, unsigned int order)
 
 	BUG_ON(PageCompound(page));
 	BUG_ON(!page_count(page));
-	for (i = 1; i < (1 << order); i++) {
-		BUG_ON(page_count(page + i));
-		set_page_count(page + i, 1);
-	}
+	for (i = 1; i < (1 << order); i++)
+		set_page_refcounted(page + i);
 }
 
 /*
@@ -1771,7 +1769,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 			continue;
 		page = pfn_to_page(pfn);
 		set_page_links(page, zone, nid, pfn);
-		set_page_count(page, 1);
+		init_page_count(page);
 		reset_page_mapcount(page);
 		SetPageReserved(page);
 		INIT_LIST_HEAD(&page->lru);