[PATCH] mm: VM_BUG_ON

Introduce a VM_BUG_ON, which is turned on with CONFIG_DEBUG_VM.  Use this
in the lightweight, inline refcounting functions; PageLRU and PageActive
checks in vmscan, because they're pretty well confined to vmscan.  And in
page allocate/free fastpaths which can be the hottest parts of the kernel
for kbuilds.

Unlike BUG_ON, VM_BUG_ON must not be used to execute statements with
side-effects, and should not be used outside core mm code.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/mm.h

@@ -278,6 +278,12 @@ struct page {
  */
 #include <linux/page-flags.h>
 
+#ifdef CONFIG_DEBUG_VM
+#define VM_BUG_ON(cond) BUG_ON(cond)
+#else
+#define VM_BUG_ON(condition) do { } while(0)
+#endif
+
 /*
  * Methods to modify the page usage count.
  *
@@ -297,7 +303,7 @@ struct page {
  */
 static inline int put_page_testzero(struct page *page)
 {
-	BUG_ON(atomic_read(&page->_count) == 0);
+	VM_BUG_ON(atomic_read(&page->_count) == 0);
 	return atomic_dec_and_test(&page->_count);
 }
 
@@ -307,6 +313,7 @@ static inline int put_page_testzero(struct page *page)
  */
 static inline int get_page_unless_zero(struct page *page)
 {
+	VM_BUG_ON(PageCompound(page));
 	return atomic_inc_not_zero(&page->_count);
 }
 
@@ -323,6 +330,7 @@ static inline void get_page(struct page *page)
 {
 	if (unlikely(PageCompound(page)))
 		page = (struct page *)page_private(page);
+	VM_BUG_ON(atomic_read(&page->_count) == 0);
 	atomic_inc(&page->_count);
 }
 

mm/internal.h

@@ -24,8 +24,8 @@ static inline void set_page_count(struct page *page, int v)
  */
 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));
+	VM_BUG_ON(PageCompound(page) && page_private(page) != (unsigned long)page);
+	VM_BUG_ON(atomic_read(&page->_count));
 	set_page_count(page, 1);
 }
 

mm/page_alloc.c

@@ -127,7 +127,6 @@ static int bad_range(struct zone *zone, struct page *page)
 
 	return 0;
 }
-
 #else
 static inline int bad_range(struct zone *zone, struct page *page)
 {
@@ -218,12 +217,12 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
 {
 	int i;
 
-	BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) == __GFP_HIGHMEM);
+	VM_BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) == __GFP_HIGHMEM);
 	/*
 	 * clear_highpage() will use KM_USER0, so it's a bug to use __GFP_ZERO
 	 * and __GFP_HIGHMEM from hard or soft interrupt context.
 	 */
-	BUG_ON((gfp_flags & __GFP_HIGHMEM) && in_interrupt());
+	VM_BUG_ON((gfp_flags & __GFP_HIGHMEM) && in_interrupt());
 	for (i = 0; i < (1 << order); i++)
 		clear_highpage(page + i);
 }
@@ -347,8 +346,8 @@ static inline void __free_one_page(struct page *page,
 
 	page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
 
-	BUG_ON(page_idx & (order_size - 1));
-	BUG_ON(bad_range(zone, page));
+	VM_BUG_ON(page_idx & (order_size - 1));
+	VM_BUG_ON(bad_range(zone, page));
 
 	zone->free_pages += order_size;
 	while (order < MAX_ORDER-1) {
@@ -421,7 +420,7 @@ static void free_pages_bulk(struct zone *zone, int count,
 	while (count--) {
 		struct page *page;
 
-		BUG_ON(list_empty(list));
+		VM_BUG_ON(list_empty(list));
 		page = list_entry(list->prev, struct page, lru);
 		/* have to delete it as __free_one_page list manipulates */
 		list_del(&page->lru);
@@ -512,7 +511,7 @@ static inline void expand(struct zone *zone, struct page *page,
 		area--;
 		high--;
 		size >>= 1;
-		BUG_ON(bad_range(zone, &page[size]));
+		VM_BUG_ON(bad_range(zone, &page[size]));
 		list_add(&page[size].lru, &area->free_list);
 		area->nr_free++;
 		set_page_order(&page[size], high);
@@ -761,8 +760,8 @@ void split_page(struct page *page, unsigned int order)
 {
 	int i;
 
-	BUG_ON(PageCompound(page));
-	BUG_ON(!page_count(page));
+	VM_BUG_ON(PageCompound(page));
+	VM_BUG_ON(!page_count(page));
 	for (i = 1; i < (1 << order); i++)
 		set_page_refcounted(page + i);
 }
@@ -809,7 +808,7 @@ again:
 	local_irq_restore(flags);
 	put_cpu();
 
-	BUG_ON(bad_range(zone, page));
+	VM_BUG_ON(bad_range(zone, page));
 	if (prep_new_page(page, order, gfp_flags))
 		goto again;
 	return page;
@@ -1083,7 +1082,7 @@ fastcall unsigned long get_zeroed_page(gfp_t gfp_mask)
 	 * get_zeroed_page() returns a 32-bit address, which cannot represent
 	 * a highmem page
 	 */
-	BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
+	VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
 
 	page = alloc_pages(gfp_mask | __GFP_ZERO, 0);
 	if (page)
@@ -1116,7 +1115,7 @@ EXPORT_SYMBOL(__free_pages);
 fastcall void free_pages(unsigned long addr, unsigned int order)
 {
 	if (addr != 0) {
-		BUG_ON(!virt_addr_valid((void *)addr));
+		VM_BUG_ON(!virt_addr_valid((void *)addr));
 		__free_pages(virt_to_page((void *)addr), order);
 	}
 }

mm/swap.c

@@ -233,7 +233,7 @@ void fastcall __page_cache_release(struct page *page)
 		struct zone *zone = page_zone(page);
 
 		spin_lock_irqsave(&zone->lru_lock, flags);
-		BUG_ON(!PageLRU(page));
+		VM_BUG_ON(!PageLRU(page));
 		__ClearPageLRU(page);
 		del_page_from_lru(zone, page);
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
@@ -284,7 +284,7 @@ void release_pages(struct page **pages, int nr, int cold)
 				zone = pagezone;
 				spin_lock_irq(&zone->lru_lock);
 			}
-			BUG_ON(!PageLRU(page));
+			VM_BUG_ON(!PageLRU(page));
 			__ClearPageLRU(page);
 			del_page_from_lru(zone, page);
 		}
@@ -337,7 +337,7 @@ void __pagevec_release_nonlru(struct pagevec *pvec)
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
 
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 		if (put_page_testzero(page))
 			pagevec_add(&pages_to_free, page);
 	}
@@ -364,7 +364,7 @@ void __pagevec_lru_add(struct pagevec *pvec)
 			zone = pagezone;
 			spin_lock_irq(&zone->lru_lock);
 		}
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
 		add_page_to_inactive_list(zone, page);
 	}
@@ -391,9 +391,9 @@ void __pagevec_lru_add_active(struct pagevec *pvec)
 			zone = pagezone;
 			spin_lock_irq(&zone->lru_lock);
 		}
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
-		BUG_ON(PageActive(page));
+		VM_BUG_ON(PageActive(page));
 		SetPageActive(page);
 		add_page_to_active_list(zone, page);
 	}

mm/vmscan.c

@@ -440,7 +440,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		if (TestSetPageLocked(page))
 			goto keep;
 
-		BUG_ON(PageActive(page));
+		VM_BUG_ON(PageActive(page));
 
 		sc->nr_scanned++;
 
@@ -564,7 +564,7 @@ keep_locked:
 		unlock_page(page);
 keep:
 		list_add(&page->lru, &ret_pages);
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 	}
 	list_splice(&ret_pages, page_list);
 	if (pagevec_count(&freed_pvec))
@@ -603,7 +603,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		page = lru_to_page(src);
 		prefetchw_prev_lru_page(page, src, flags);
 
-		BUG_ON(!PageLRU(page));
+		VM_BUG_ON(!PageLRU(page));
 
 		list_del(&page->lru);
 		target = src;
@@ -674,7 +674,7 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 		 */
 		while (!list_empty(&page_list)) {
 			page = lru_to_page(&page_list);
-			BUG_ON(PageLRU(page));
+			VM_BUG_ON(PageLRU(page));
 			SetPageLRU(page);
 			list_del(&page->lru);
 			if (PageActive(page))
@@ -797,9 +797,9 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 	while (!list_empty(&l_inactive)) {
 		page = lru_to_page(&l_inactive);
 		prefetchw_prev_lru_page(page, &l_inactive, flags);
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
-		BUG_ON(!PageActive(page));
+		VM_BUG_ON(!PageActive(page));
 		ClearPageActive(page);
 
 		list_move(&page->lru, &zone->inactive_list);
@@ -827,9 +827,9 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 	while (!list_empty(&l_active)) {
 		page = lru_to_page(&l_active);
 		prefetchw_prev_lru_page(page, &l_active, flags);
-		BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
-		BUG_ON(!PageActive(page));
+		VM_BUG_ON(!PageActive(page));
 		list_move(&page->lru, &zone->active_list);
 		pgmoved++;
 		if (!pagevec_add(&pvec, page)) {