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: 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5d9b4c9813bd..5568553a41fd 100644
--- a/include/linux/mm.h
+++ b/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 */