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Date: Tue, 23 Aug 2016 14:56:19 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Waiman Long <waiman.long@hpe.com>, Jason Low <jason.low2@hpe.com>,
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        Imre Deak <imre.deak@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Tim Chen <tim.c.chen@linux.intel.com>, Terry Rudd <terry.rudd@hpe.com>,
        "Paul E. McKenney" <paulmck@us.ibm.com>, Jason Low <jason.low2@hp.com>
Subject: Re: [RFC][PATCH 3/3] locking/mutex: Add lock handoff to avoid
 starvation
Message-ID: <20160823125619.GC10138@twins.programming.kicks-ass.net>
References: <20160823124617.015645861@infradead.org>
 <20160823124856.898171453@infradead.org>
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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.