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 S934132AbaCSQ5z (ORCPT <rfc822;w@1wt.eu>);
	Wed, 19 Mar 2014 12:57:55 -0400
Received: from merlin.infradead.org ([205.233.59.134]:39429 "EHLO
	merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1755729AbaCSQ5y (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 19 Mar 2014 12:57:54 -0400
Date: Wed, 19 Mar 2014 17:57:47 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peng Tao <bergwolf@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Oleg Drokin <oleg.drokin@intel.com>,
        Andreas Dilger <andreas.dilger@intel.com>
Subject: Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive_head
Message-ID: <20140319165747.GC8557@laptop.programming.kicks-ass.net>
References: <1395148208-2209-1-git-send-email-bergwolf@gmail.com>
 <20140318133331.GA23193@laptop.programming.kicks-ass.net>
 <CA+a=Yy74V9_N4L8DoG=6iLnjGyOb6=ifraAqs5jW7ZsCG0t7jw@mail.gmail.com>
 <20140318140504.GD23193@laptop.programming.kicks-ass.net>
 <20140318154724.GA5669@redhat.com>
 <CA+a=Yy4WPO9FQwqzDygz6AadT6xbOMEa_puwosZ6WFN17uCncw@mail.gmail.com>
 <20140319164907.GA10113@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20140319164907.GA10113@redhat.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Mar 19, 2014 at 05:49:07PM +0100, Oleg Nesterov wrote:
> +static void add_wait_queue_flag(wait_queue_head_t *q, wait_queue_t *wait)
> +{
> +	struct list_head *head = &q->task_list;
> +	wait_queue_t *excl;
> +
> +	if (wait->flags & WQ_FLAG_EXCLUSIVE) {
> +		if (wait->flags & WQ_FLAG_EXCLUSIVE_HEAD) {
> +			list_for_each_entry(excl, head, task_list)
> +				if (excl->flags & WQ_FLAG_EXCLUSIVE) {
> +					head = &excl->task_list;
> +					break;
> +				}

I prefer an extra pair of { } here, but the main concern would be the
cost of that iteration.

> +		}
> +		/* turn list_add() below into list_add_tail() */
> +		head = head->prev;
> +	}
> +
> +	list_add(&wait->task_list, head);
> +}

Other than that, yes something like that would do I suppose.