Mutexs will exceed 64 bytes for debug builds in 2.6.31 kernels.

Increase the pad size accordingly to handle this.

module/zfs/arc.c

@@ -517,7 +517,7 @@ static void arc_evict_ghost(arc_state_t *state, uint64_t spa, int64_t bytes);
  * Hash table routines
  */
 
-#define	HT_LOCK_PAD	64
+#define	HT_LOCK_PAD	256
 
 struct ht_lock {
 	kmutex_t	ht_lock;