---

yaml
---
r: 283003
b: refs/heads/master
c: c0a32fc
h: refs/heads/master
i:
  283001: 090aafa
  282999: 0e3c73d
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 1399ff86f2a2bbacbbe68fa00c5f8c752b344723
+refs/heads/master: c0a32fc5a2e470d0b02597b23ad79a317735253e

trunk/Documentation/kernel-parameters.txt

@@ -623,6 +623,25 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	no_debug_objects
 			[KNL] Disable object debugging
 
+	debug_guardpage_minorder=
+			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
+			parameter allows control of the order of pages that will
+			be intentionally kept free (and hence protected) by the
+			buddy allocator. Bigger value increase the probability
+			of catching random memory corruption, but reduce the
+			amount of memory for normal system use. The maximum
+			possible value is MAX_ORDER/2.  Setting this parameter
+			to 1 or 2 should be enough to identify most random
+			memory corruption problems caused by bugs in kernel or
+			driver code when a CPU writes to (or reads from) a
+			random memory location. Note that there exists a class
+			of memory corruptions problems caused by buggy H/W or
+			F/W or by drivers badly programing DMA (basically when
+			memory is written at bus level and the CPU MMU is
+			bypassed) which are not detectable by
+			CONFIG_DEBUG_PAGEALLOC, hence this option will not help
+			tracking down these problems.
+
 	debugpat	[X86] Enable PAT debugging
 
 	decnet.addr=	[HW,NET]

trunk/include/linux/mm.h

@@ -1618,5 +1618,22 @@ extern void copy_user_huge_page(struct page *dst, struct page *src,
 				unsigned int pages_per_huge_page);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+extern unsigned int _debug_guardpage_minorder;
+
+static inline unsigned int debug_guardpage_minorder(void)
+{
+	return _debug_guardpage_minorder;
+}
+
+static inline bool page_is_guard(struct page *page)
+{
+	return test_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+}
+#else
+static inline unsigned int debug_guardpage_minorder(void) { return 0; }
+static inline bool page_is_guard(struct page *page) { return false; }
+#endif /* CONFIG_DEBUG_PAGEALLOC */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */

trunk/include/linux/page-debug-flags.h

@@ -13,6 +13,7 @@
 
 enum page_debug_flags {
 	PAGE_DEBUG_FLAG_POISON,		/* Page is poisoned */
+	PAGE_DEBUG_FLAG_GUARD,
 };
 
 /*
@@ -21,7 +22,8 @@ enum page_debug_flags {
  */
 
 #ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
-#if !defined(CONFIG_PAGE_POISONING) \
+#if !defined(CONFIG_PAGE_POISONING) && \
+    !defined(CONFIG_PAGE_GUARD) \
 /* && !defined(CONFIG_PAGE_DEBUG_SOMETHING_ELSE) && ... */
 #error WANT_PAGE_DEBUG_FLAGS is turned on with no debug features!
 #endif

trunk/mm/Kconfig.debug

@@ -4,6 +4,7 @@ config DEBUG_PAGEALLOC
 	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
 	depends on !KMEMCHECK
 	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
+	select PAGE_GUARD if ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	---help---
 	  Unmap pages from the kernel linear mapping after free_pages().
 	  This results in a large slowdown, but helps to find certain types
@@ -22,3 +23,7 @@ config WANT_PAGE_DEBUG_FLAGS
 config PAGE_POISONING
 	bool
 	select WANT_PAGE_DEBUG_FLAGS
+
+config PAGE_GUARD
+	bool
+	select WANT_PAGE_DEBUG_FLAGS

trunk/mm/page_alloc.c

@@ -57,6 +57,7 @@
 #include <linux/ftrace_event.h>
 #include <linux/memcontrol.h>
 #include <linux/prefetch.h>
+#include <linux/page-debug-flags.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -388,6 +389,37 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
 		clear_highpage(page + i);
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+unsigned int _debug_guardpage_minorder;
+
+static int __init debug_guardpage_minorder_setup(char *buf)
+{
+	unsigned long res;
+
+	if (kstrtoul(buf, 10, &res) < 0 ||  res > MAX_ORDER / 2) {
+		printk(KERN_ERR "Bad debug_guardpage_minorder value\n");
+		return 0;
+	}
+	_debug_guardpage_minorder = res;
+	printk(KERN_INFO "Setting debug_guardpage_minorder to %lu\n", res);
+	return 0;
+}
+__setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
+
+static inline void set_page_guard_flag(struct page *page)
+{
+	__set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+}
+
+static inline void clear_page_guard_flag(struct page *page)
+{
+	__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+}
+#else
+static inline void set_page_guard_flag(struct page *page) { }
+static inline void clear_page_guard_flag(struct page *page) { }
+#endif
+
 static inline void set_page_order(struct page *page, int order)
 {
 	set_page_private(page, order);
@@ -445,6 +477,11 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
 	if (page_zone_id(page) != page_zone_id(buddy))
 		return 0;
 
+	if (page_is_guard(buddy) && page_order(buddy) == order) {
+		VM_BUG_ON(page_count(buddy) != 0);
+		return 1;
+	}
+
 	if (PageBuddy(buddy) && page_order(buddy) == order) {
 		VM_BUG_ON(page_count(buddy) != 0);
 		return 1;
@@ -501,11 +538,19 @@ static inline void __free_one_page(struct page *page,
 		buddy = page + (buddy_idx - page_idx);
 		if (!page_is_buddy(page, buddy, order))
 			break;
-
-		/* Our buddy is free, merge with it and move up one order. */
-		list_del(&buddy->lru);
-		zone->free_area[order].nr_free--;
-		rmv_page_order(buddy);
+		/*
+		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
+		 * merge with it and move up one order.
+		 */
+		if (page_is_guard(buddy)) {
+			clear_page_guard_flag(buddy);
+			set_page_private(page, 0);
+			__mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);
+		} else {
+			list_del(&buddy->lru);
+			zone->free_area[order].nr_free--;
+			rmv_page_order(buddy);
+		}
 		combined_idx = buddy_idx & page_idx;
 		page = page + (combined_idx - page_idx);
 		page_idx = combined_idx;
@@ -731,6 +776,23 @@ static inline void expand(struct zone *zone, struct page *page,
 		high--;
 		size >>= 1;
 		VM_BUG_ON(bad_range(zone, &page[size]));
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+		if (high < debug_guardpage_minorder()) {
+			/*
+			 * Mark as guard pages (or page), that will allow to
+			 * merge back to allocator when buddy will be freed.
+			 * Corresponding page table entries will not be touched,
+			 * pages will stay not present in virtual address space
+			 */
+			INIT_LIST_HEAD(&page[size].lru);
+			set_page_guard_flag(&page[size]);
+			set_page_private(&page[size], high);
+			/* Guard pages are not available for any usage */
+			__mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << high));
+			continue;
+		}
+#endif
 		list_add(&page[size].lru, &area->free_list[migratetype]);
 		area->nr_free++;
 		set_page_order(&page[size], high);
@@ -1754,7 +1816,8 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...)
 {
 	unsigned int filter = SHOW_MEM_FILTER_NODES;
 
-	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
+	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) ||
+	    debug_guardpage_minorder() > 0)
 		return;
 
 	/*