[PATCH] lockdep: debug_show_all_locks & debug_show_held_locks vs. debug_locks

lockdep's data shouldn't be used when debug_locks == 0 because it's not
updated after this, so it's more misleading than helpful.

PS: probably lockdep's current-> fields should be reset after it turns
debug_locks off: so, after printing a bug report, but before return from
exported functions, but there are really a lot of these possibilities (e.g.
 after DEBUG_LOCKS_WARN_ON), so, something could be missed.  (Of course
direct use of this fields isn't recommended either.)

Reported-by: Folkert van Heusden <folkert@vanheusden.com>
Inspired-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 8dc24c92dc6d..7065a687ac54 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2742,6 +2742,10 @@ void debug_show_all_locks(void)
         int count = 10;
         int unlock = 1;
 
+        if (unlikely(!debug_locks)) {
+                printk("INFO: lockdep is turned off.\n");
+                return;
+        }
         printk("\nShowing all locks held in the system:\n");
 
         /*
@@ -2785,6 +2789,10 @@ EXPORT_SYMBOL_GPL(debug_show_all_locks);
 
 void debug_show_held_locks(struct task_struct *task)
 {
+        if (unlikely(!debug_locks)) {
+                printk("INFO: lockdep is turned off.\n");
+                return;
+        }
         lockdep_print_held_locks(task);
 }