linux-kernel - Re: [PATCH v2] neighbour: confirm neigh entries when ARP packet is received

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Message-ID: <20180911111217.3e3679c5@xeon-e3>
Date:   Tue, 11 Sep 2018 11:12:17 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Vasily Khoruzhick <vasilykh@...sta.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jim Westfall <jwestfall@...realistic.net>,
        Wolfgang Bumiller <w.bumiller@...xmox.com>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Ihar Hrachyshka <ihrachys@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] neighbour: confirm neigh entries when ARP packet is
 received

On Tue, 11 Sep 2018 11:04:06 -0700
Vasily Khoruzhick <vasilykh@...sta.com> wrote:

> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index aa19d86937af..56a554597db5 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -1180,6 +1180,12 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
>  		lladdr = neigh->ha;
>  	}
>  
> +	/* Update confirmed timestamp for neighbour entry after we
> +	 * received ARP packet even if it doesn't change IP to MAC binding.
> +	 */
> +	if (new & NUD_CONNECTED)
> +		neigh->confirmed = jiffies;

You might want to do:
	if ((new & NUD_CONNECTED) && neigh->confirmed != jiffies)
		neigh->confirmed = jiffies;

This avoid poisoning the cacheline with unnecessary write.