mm/vmstat.c: assert that vmstat_text is in sync with stat_items_size

Having two gigantic arrays that must manually be kept in sync, including
ifdefs, isn't exactly robust.  To make it easier to catch such issues in
the future, add a BUILD_BUG_ON().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Jann Horn <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Kemi Wang <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmstat.c

@@ -1665,6 +1665,8 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 	stat_items_size += sizeof(struct vm_event_state);
 #endif
 
+	BUILD_BUG_ON(stat_items_size !=
+		     ARRAY_SIZE(vmstat_text) * sizeof(unsigned long));
 	v = kmalloc(stat_items_size, GFP_KERNEL);
 	m->private = v;
 	if (!v)