locking/lockdep: Only ask for /proc/lock_stat output when available

When lockdep turns itself off, the following message is logged:

  Please attach the output of /proc/lock_stat to the bug report

Omit this message when CONFIG_LOCK_STAT is off, and /proc/lock_stat
doesn't exist.

Signed-off-by: Andreas Gruenbacher <andreas.gruenbacher@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1405451452-3824-1-git-send-email-andreas.gruenbacher@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/lockdep.c

@@ -384,7 +384,9 @@ static void print_lockdep_off(const char *bug_msg)
 {
 	printk(KERN_DEBUG "%s\n", bug_msg);
 	printk(KERN_DEBUG "turning off the locking correctness validator.\n");
+#ifdef CONFIG_LOCK_STAT
 	printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report\n");
+#endif
 }
 
 static int save_trace(struct stack_trace *trace)