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, 19 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7b2e5c5eefa6..7ed7030e7722 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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]