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

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Message-ID: <20160823125619.GC10138@twins.programming.kicks-ass.net>
Date:   Tue, 23 Aug 2016 14:56:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Waiman Long <waiman.long@....com>,
        Jason Low <jason.low2@....com>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <Will.Deacon@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Imre Deak <imre.deak@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Terry Rudd <terry.rudd@....com>,
        "Paul E. McKenney" <paulmck@...ibm.com>,
        Jason Low <jason.low2@...com>
Subject: Re: [RFC][PATCH 3/3] locking/mutex: Add lock handoff to avoid
 starvation

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.