From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932477AbcHKCja (ORCPT <rfc822;w@1wt.eu>);
	Wed, 10 Aug 2016 22:39:30 -0400
Received: from g2t4622.austin.hp.com ([15.73.212.79]:50556 "EHLO
	g2t4622.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752164AbcHKCj3 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 10 Aug 2016 22:39:29 -0400
Message-ID: <1470882626.17361.18.camel@j-VirtualBox>
Subject: Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning
 is enabled
From: Jason Low <jason.low2@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: jason.low2@hpe.com, Ingo Molnar <mingo@redhat.com>, imre.deak@intel.com,
        linux-kernel@vger.kernel.org, Waiman Long <Waiman.Long@hpe.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Tim Chen <tim.c.chen@linux.intel.com>, terry.rudd@hpe.com,
        "Paul E. McKenney" <paulmck@us.ibm.com>
Date: Wed, 10 Aug 2016 19:30:26 -0700
In-Reply-To: <1470854648.17361.9.camel@j-VirtualBox>
References: <1470854648.17361.9.camel@j-VirtualBox>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.10.4-0ubuntu2 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2016-08-10 at 11:44 -0700, Jason Low wrote:
> @@ -917,11 +976,12 @@ EXPORT_SYMBOL(mutex_trylock);
>  int __sched
>  __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  {
> -	int ret;
> +	int ret = 1;
>  
>  	might_sleep();
>  
> -	ret = __mutex_fastpath_lock_retval(&lock->base.count);
> +	if (!need_yield_to_waiter(lock))
> +		ret = __mutex_fastpath_lock_retval(&lock->base.count);
>  
>  	if (likely(!ret)) {
>  		ww_mutex_set_context_fastpath(lock, ctx);
> @@ -935,11 +995,12 @@ EXPORT_SYMBOL(__ww_mutex_lock);
>  int __sched
>  __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  {
> -	int ret;
> +	int ret = 1;
>  
>  	might_sleep();
>  
> -	ret = __mutex_fastpath_lock_retval(&lock->base.count);
> +	if (!need_yield_to_waiter(lock))

And we would need to pass &lock->base instead of lock since lock is
struct ww_mutex * here.