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Commit c0a32fc5 authored by Stanislaw Gruszka's avatar Stanislaw Gruszka Committed by Linus Torvalds
Browse files

mm: more intensive memory corruption debugging 



With CONFIG_DEBUG_PAGEALLOC configured, the CPU will generate an exception
on access (read,write) to an unallocated page, which permits us to catch
code which corrupts memory.  However the kernel is trying to maximise
memory usage, hence there are usually few free pages in the system and
buggy code usually corrupts some crucial data.

This patch changes the buddy allocator to keep more free/protected pages
and to interlace free/protected and allocated pages to increase the
probability of catching corruption.

When the kernel is compiled with CONFIG_DEBUG_PAGEALLOC,
debug_guardpage_minorder defines the minimum order used by the page
allocator to grant a request.  The requested size will be returned with
the remaining pages used as guard pages.

The default value of debug_guardpage_minorder is zero: no change from
current behaviour.

[akpm@linux-foundation.org: tweak documentation, s/flg/flag/]
Signed-off-by: default avatarStanislaw Gruszka <sgruszka@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1399ff86

Documentation/kernel-parameters.txt

+19 −0
Original line number Diff line number Diff line
@@ -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]

include/linux/mm.h

+17 −0
Original line number Diff line number Diff line
@@ -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 */

include/linux/page-debug-flags.h

+3 −1
Original line number Diff line number Diff line
@@ -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

mm/Kconfig.debug

+5 −0
Original line number Diff line number Diff line
@@ -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

mm/page_alloc.c

+69 −6
Original line number Diff line number Diff line
@@ -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. */

		/*

		 * 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;



	/*