While debugging the unlock vs. dequeue race which resulted in state corruption of futexes the lockless nature of rt_mutex_proxy_unlock() caused some confusion. Add commentry to explain why it is safe to do this lockless. Add matching comments to rt_mutex_init_proxy_locked() for completeness sake. Signed-off-by: Thomas Gleixner --- kernel/locking/rtmutex.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1617,11 +1617,15 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init); * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a * proxy owner * - * @lock: the rt_mutex to be locked + * @lock: the rt_mutex to be locked * @proxy_owner:the task to set as owner * * No locking. Caller has to do serializing itself - * Special API call for PI-futex support + * + * Special API call for PI-futex support. This initializes the rtmutex and + * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not + * possible at this point because the pi_state which contains the rtmutex + * is not yet visible to other tasks. */ void rt_mutex_init_proxy_locked(struct rt_mutex *lock, struct task_struct *proxy_owner) @@ -1635,10 +1639,14 @@ void rt_mutex_init_proxy_locked(struct r /** * rt_mutex_proxy_unlock - release a lock on behalf of owner * - * @lock: the rt_mutex to be locked + * @lock: the rt_mutex to be locked * * No locking. Caller has to do serializing itself - * Special API call for PI-futex support + * + * Special API call for PI-futex support. This merily cleans up the rtmutex + * (debugging) state. Concurrent operations on this rt_mutex are not + * possible because it belongs to the pi_state which is about to be freed + * and it is not longer visible to other tasks. */ void rt_mutex_proxy_unlock(struct rt_mutex *lock, struct task_struct *proxy_owner)