Re: [RFC][PATCH 3/3] locking/mutex: Add lock handoff to avoid starvation

[Peter Zijlstra]

On Tue, Aug 23, 2016 at 02:46:20PM +0200, Peter Zijlstra wrote:
> @@ -573,8 +600,14 @@ __mutex_lock_common(struct mutex *lock,
>  		schedule_preempt_disabled();
>  		spin_lock_mutex(&lock->wait_lock, flags);
>  
> +		if (__mutex_owner(lock) == current)
> +			break;
> +
>  		if (__mutex_trylock(lock))
>  			break;
> +
> +		if (__mutex_waiter_is_first(lock, &waiter))
> +			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
>  	}
>  	__set_task_state(task, TASK_RUNNING);
>  

And 'obviously' we can add a spin-on-owner loop in there as well, as
Waiman's patches did, but I didn't bother pulling that in for now.