From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next 01/17] net: sched: refactor
 mini_qdisc_pair_swap() to use workqueue
Date: Tue, 13 Nov 2018 08:08:31 -0800 (PST)
Message-ID: <20181113.080831.1579511935763457972.davem@davemloft.net>
References: <1542009346-23780-2-git-send-email-vladbu@mellanox.com>
        <20181112.092809.744587974364715455.davem@davemloft.net>
        <vbfk1lhjf2s.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: netdev@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com,
        jiri@resnulli.us, ast@kernel.org, daniel@iogearbox.net
To: vladbu@mellanox.com
Return-path: <netdev-owner@vger.kernel.org>
Received: from shards.monkeyblade.net ([23.128.96.9]:51446 "EHLO
        shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1731439AbeKNCIM (ORCPT
        <rfc822;netdev@vger.kernel.org>); Tue, 13 Nov 2018 21:08:12 -0500
In-Reply-To: <vbfk1lhjf2s.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

From: Vlad Buslov <vladbu@mellanox.com>
Date: Tue, 13 Nov 2018 13:13:19 +0000

> 
> On Mon 12 Nov 2018 at 17:28, David Miller <davem@davemloft.net> wrote:
>> From: Vlad Buslov <vladbu@mellanox.com>
>> Date: Mon, 12 Nov 2018 09:55:30 +0200
>>
>>> +void mini_qdisc_pair_swap(struct mini_Qdisc_pair *miniqp,
>>> +			  struct tcf_proto *tp_head)
>>> +{
>>> +	xchg(&miniqp->tp_head, tp_head);
>>
>> If you are not checking the return value of xchg(), then this is
>> simply a store with optionally a memory barrier of some sort
>> either before or after.
> 
> That was my intention. What would be a better way to atomically
> reset a pointer? Should I just change this line to explicit
> assignment+barrier?

We have all kinds of helpers in the kernel for doing things like
this, grep for things like "smp_load_acquire", "smp_store_release()"
etc.