linux-kernel - Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning is enabled

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Message-ID: <20160818141404.GA10121@twins.programming.kicks-ass.net>
Date:	Thu, 18 Aug 2016 16:14:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Low <jason.low2@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, imre.deak@...el.com,
	linux-kernel@...r.kernel.org, Jason Low <jason.low2@...com>,
	Waiman Long <Waiman.Long@....com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Tim Chen <tim.c.chen@...ux.intel.com>, terry.rudd@....com,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning
 is enabled

On Wed, Aug 10, 2016 at 11:44:08AM -0700, Jason Low wrote:
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 2cb7531..5643a233 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -57,6 +57,8 @@ struct mutex {
>  #endif
>  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
>  	struct optimistic_spin_queue osq; /* Spinner MCS lock */
> +#elif defined(CONFIG_SMP)
> +	bool yield_to_waiter; /* Prevent starvation when spinning disabled */
>  #endif
>  #ifdef CONFIG_DEBUG_MUTEXES
>  	void			*magic;

Isn't this also possible on !SMP && PREEMPT ?