netdev - Re: [PATCH v3 net] net: ipv6: regenerate host route if moved to gc list

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Message-ID: <20170424210819.5ynqc6rdf7z2gnox@kafai-mba.dhcp.thefacebook.com>
Date:   Mon, 24 Apr 2017 14:08:19 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     David Ahern <dsa@...ulusnetworks.com>
CC:     Eric Dumazet <eric.dumazet@...il.com>, <netdev@...r.kernel.org>,
        <dvyukov@...gle.com>, <andreyknvl@...gle.com>,
        <mmanning@...cade.com>
Subject: Re: [PATCH v3 net] net: ipv6: regenerate host route if moved to gc
 list

On Mon, Apr 24, 2017 at 01:37:00PM -0600, David Ahern wrote:
> On 4/24/17 10:39 AM, Eric Dumazet wrote:
> >
> > Very nice changelog !
>
>
> Thanks. Given my aggressive brain cell recycling program, I needed to
> write down the analysis.
>
>
>
> >> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> >> index 80ce478c4851..93f81d9cd85f 100644
> >> --- a/net/ipv6/addrconf.c
> >> +++ b/net/ipv6/addrconf.c
> >> @@ -3271,14 +3271,25 @@ static void addrconf_gre_config(struct net_device *dev)
> >>  static int fixup_permanent_addr(struct inet6_dev *idev,
> >>  				struct inet6_ifaddr *ifp)
> >>  {
> >> -	if (!ifp->rt) {
> >> -		struct rt6_info *rt;
> >> +	/* rt6i_ref == 0 means the host route was removed from the
> >> +	 * FIB, for example, if 'lo' device is taken down. In that
> >> +	 * case regenerate the host route.
> >> +	 */
> >> +	if (!ifp->rt || !atomic_read(&ifp->rt->rt6i_ref)) {
> >> +		struct rt6_info *rt, *prev;
> >>
> >>  		rt = addrconf_dst_alloc(idev, &ifp->addr, false);
> >>  		if (unlikely(IS_ERR(rt)))
> >>  			return PTR_ERR(rt);
> >>
> >> +		prev = ifp->rt;
> >
> > I would feel more comfortable if this was moved after the spin_lock() ?
>
> That's what I had in v2; it reads better to me even if it is not
> technically required (all changes to ifp->rt happen under rtnl).
>
> Martin you agree?
Agree.

My question was mainly on the added spin_lock.

>
> I'll send a v3 tomorrow -- allow more time for other comments.