lockdep: fix overflow in the hlock shrinkage code

There is a overflow by 1 case in the new shrunken hlock code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 67f42b300c65..c88aa3d8e87f 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -191,7 +191,12 @@ struct lock_chain {
 };
 
 #define MAX_LOCKDEP_KEYS_BITS           11
-#define MAX_LOCKDEP_KEYS                (1UL << MAX_LOCKDEP_KEYS_BITS)
+/*
+ * Subtract one because we offset hlock->class_idx by 1 in order
+ * to make 0 mean no class. This avoids overflowing the class_idx
+ * bitfield and hitting the BUG in hlock_class().
+ */
+#define MAX_LOCKDEP_KEYS                ((1UL << MAX_LOCKDEP_KEYS_BITS) - 1)
 
 struct held_lock {
         /*