From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH net-next 2/8] rtnetlink: add rtnl_register_module
Date: Mon, 6 Nov 2017 13:44:54 +0100
Message-ID: <20171106124454.GI3165@worktop.lehotels.local>
References: <20171106105113.20476-1-fw@strlen.de>
 <20171106105113.20476-3-fw@strlen.de>
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Cc: netdev@vger.kernel.org
To: Florian Westphal <fw@strlen.de>
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On Mon, Nov 06, 2017 at 11:51:07AM +0100, Florian Westphal wrote:
> @@ -180,6 +164,12 @@ int __rtnl_register(int protocol, int msgtype,
>  		rcu_assign_pointer(rtnl_msg_handlers[protocol], tab);
>  	}
>  
> +	WARN_ON(tab[msgindex].owner && tab[msgindex].owner != owner);
> +
> +	tab[msgindex].owner = owner;
> +	/* make sure owner is always visible first */
> +	smp_wmb();
> +
>  	if (doit)
>  		tab[msgindex].doit = doit;
>  	if (dumpit)

> @@ -235,6 +279,9 @@ int rtnl_unregister(int protocol, int msgtype)
>  	handlers[msgindex].doit = NULL;
>  	handlers[msgindex].dumpit = NULL;
>  	handlers[msgindex].flags = 0;
> +	/* make sure we clear owner last */
> +	smp_wmb();
> +	handlers[msgindex].owner = NULL;
>  	rtnl_unlock();
>  
>  	return 0;

These wmb()'s don't make sense; and the comments are incomplete. What do
they pair with? Who cares about this ordering?