Re: [PATCH -v5 09/14] futex: Rework inconsistent rt_mutex/futex_q state

[Thomas Gleixner]

On Sat, 4 Mar 2017, Peter Zijlstra wrote:
> @@ -1402,12 +1402,18 @@ static int wake_futex_pi(u32 __user *uad
>  	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
>  
>  	/*
> -	 * It is possible that the next waiter (the one that brought
> -	 * top_waiter owner to the kernel) timed out and is no longer
> -	 * waiting on the lock.
> +	 * When we interleave with futex_lock_pi() where it does
> +	 * rt_mutex_timed_futex_lock(), we might observe @this futex_q waiter,
> +	 * but the rt_mutex's wait_list can be empty (either still, or again,
> +	 * depending on which side we land).
> +	 *
> +	 * When this happens, give up our locks and try again, giving the
> +	 * futex_lock_pi() instance time to complete and unqueue_me().

  time to complete, either by waiting on the rtmutex or removing itself
  from the futex queue.

Or something like that.

Thanks,

	tglx