1 files changed, 27 insertions, 0 deletions
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 0b2a79c4013b..cbff35b9b7ae 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -20,6 +20,33 @@ struct mutex_waiter {
 #endif
 };
 
+/*
+ * @owner: contains: 'struct task_struct *' to the current lock owner,
+ * NULL means not owned. Since task_struct pointers are aligned at
+ * at least L1_CACHE_BYTES, we have low bits to store extra state.
+ *
+ * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
+ * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ * Bit2 indicates handoff has been done and we're waiting for pickup.
+ */
+#define MUTEX_FLAG_WAITERS	0x01
+#define MUTEX_FLAG_HANDOFF	0x02
+#define MUTEX_FLAG_PICKUP	0x04
+
+#define MUTEX_FLAGS		0x07
+
+/*
+ * Internal helper function; C doesn't allow us to hide it :/
+ *
+ * DO NOT USE (outside of mutex & scheduler code).
+ */
+static inline struct task_struct *__mutex_owner(struct mutex *lock)
+{
+	if (!lock)
+		return NULL;
+	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
+}
+
 #ifdef CONFIG_DEBUG_MUTEXES
 extern void debug_mutex_lock_common(struct mutex *lock,
 				    struct mutex_waiter *waiter);