Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 11 Sep 2018 11:12:17 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Vasily Khoruzhick <vasilykh@arista.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Roopa Prabhu <roopa@cumulusnetworks.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        Jim Westfall <jwestfall@surrealistic.net>,
        Wolfgang Bumiller <w.bumiller@proxmox.com>,
        Vasily Khoruzhick <anarsoul@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Ihar Hrachyshka <ihrachys@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] neighbour: confirm neigh entries when ARP packet is
 received
Message-ID: <20180911111217.3e3679c5@xeon-e3>
In-Reply-To: <20180911180406.31283-1-vasilykh@arista.com>
References: <20180911180406.31283-1-vasilykh@arista.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 11 Sep 2018 11:04:06 -0700
Vasily Khoruzhick <vasilykh@arista.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.