mm: add CONFIG_DEBUG_VM_RB build option

Add a CONFIG_DEBUG_VM_RB build option for the previously existing
DEBUG_MM_RB code.  Now that Andi Kleen modified it to avoid using
recursive algorithms, we can expose it a bit more.

Also extend this code to validate_mm() after stack expansion, and to check
that the vma's start and last pgoffs have not changed since the nodes were
inserted on the anon vma interval tree (as it is important that the nodes
be reindexed after each such update).

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -798,6 +798,15 @@ config DEBUG_VM
 
 	  If unsure, say N.
 
+config DEBUG_VM_RB
+	bool "Debug VM red-black trees"
+	depends on DEBUG_VM
+	help
+	  Enable this to turn on more extended checks in the virtual-memory
+	  system that may impact performance.
+
+	  If unsure, say N.
+
 config DEBUG_VIRTUAL
 	bool "Debug VM translations"
 	depends on DEBUG_KERNEL && X86