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.

Signed-off-by: Stanislaw 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: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 0b53aad7fed841e80044d315aff5d205333f8bc9..9906afe52b65f9c260f923ce3d90de314c64fc92 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -623,6 +623,24 @@ 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 order of pages that will be
+                       intentionally kept free (and hence protected) by buddy
+                       allocator. Bigger value increase probability of
+                       catching random memory corruption, but reduce amount
+                       of memory for normal system use. 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/drivers
+                       code when CPU write to (or read from) random memory
+                       location. Note that there exist 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 CPU MMU is bypassed), which
+                       are not detectable by CONFIG_DEBUG_PAGEALLOC, hence this
+                       option would not help tracking down these problems too.
+
        debugpat        [X86] Enable PAT debugging
 
        decnet.addr=    [HW,NET]

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 02e39b0042b16978f4d2868933ed17df23c334eb..91b72c9b3c0e2afb332bd140d4d3d0b0a082ae88 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1608,5 +1608,22 @@ 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 */

diff --git a/include/linux/page-debug-flags.h b/include/linux/page-debug-flags.h
index b0638fd91e92fdacc2f2675207ef723342072597..22691f614043df3d3cdf77c3b12dd97a551bf813 100644 (file)
--- a/include/linux/page-debug-flags.h
+++ b/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

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 8b1a477162dc07242e7a461951bca291cff3dde7..4b2443254de260d2e05cdecb8d3eea903d91734f 100644 (file)
--- a/mm/Kconfig.debug
+++ b/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

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 76db4e2ad51796ec1ac6819c4a6fe4ada077f25b..8b13233f851fb6545d0420a85c4e97f464367473 100644 (file)
--- a/mm/page_alloc.c
+++ b/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>
@@ -401,6 +402,37 @@ 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_flg(struct page *page)
+{
+       __set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+}
+
+static inline void clear_page_guard_flg(struct page *page)
+{
+       __clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+}
+#else
+static inline void set_page_guard_flg(struct page *page) { }
+static inline void clear_page_guard_flg(struct page *page) { }
+#endif
+
 static inline void set_page_order(struct page *page, int order)
 {
        set_page_private(page, order);
@@ -458,6 +490,11 @@ 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;
@@ -514,11 +551,19 @@ 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_flg(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;
@@ -744,6 +789,23 @@ 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_flg(&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);
@@ -1767,7 +1829,8 @@ 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;
 
        /*