netdev - Re: [PATCH ipsec,v3] net: xfrm_policy: fix device unregistration hang

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Date:   Wed, 14 Feb 2018 10:24:46 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Eyal Birger <eyal.birger@...il.com>
CC:     Xin Long <lucien.xin@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Wei Wang <weiwan@...gle.com>, davem <davem@...emloft.net>,
        network dev <netdev@...r.kernel.org>,
        Florian Westphal <fw@...len.de>, <shmulik@...anetworks.com>,
        <shannon.nelson@...cle.com>
Subject: Re: [PATCH ipsec,v3] net: xfrm_policy: fix device unregistration hang

On Tue, Feb 13, 2018 at 08:23:14PM +0200, Eyal Birger wrote:
> Hi Xin Long,
> 
> On Tue, 13 Feb 2018 23:18:14 +0800
> Xin Long <lucien.xin@...il.com> wrote:
> 
> > On Tue, Feb 13, 2018 at 6:54 PM, Eyal Birger <eyal.birger@...il.com>
> > wrote:
> > > In setups like the following:
> > >
> > >        Host A          --        Host B
> > > tun0 -- ipsec -- eth0  --  eth0 -- ipsec -- tun0
> > >
> > > where tun0 are tunnel devices using dst_cache (ipip, ipip6, etc...).
> > >
> > > Unregistration of an underlying eth0 device leads to the following
> > > log messages:
> > >
> > > unregister_netdevice: waiting for eth0 to become free. Usage count
> > > = 2
> > >
> > > This is since xfrm dsts device references are not released upon
> > > device unregistration when the xfrm dst is cached in a dst_cache.
> > >
> > > This issue was first introduced in commit 52df157f17e5
> > > ("xfrm: take refcnt of dst when creating struct xfrm_dst bundle")
> > > as part of an effort to remove routing garbage collection.
> > >
> > > Several approaches for fixing this were discussed in [1]; this
> > > commit keeps track of allocated xdsts and releases their device
> > > references on a netdev unregister/down events.
> > >
> > > Signed-off-by: Eyal Birger <eyal.birger@...il.com>
> > > Fixes: 52df157f17e5 ("xfrm: take refcnt of dst when creating struct
> > > xfrm_dst bundle")  
> > I had another fix [1] for this issue in my local tree.
> > That reuses uncached_list to track xdsts, and fewer job to do for
> > this. As naturally uncached_list is already the list that is supposed
> > to do this job. We don't have to introduce a new list and members.
> > 
> > [1] https://paste.fedoraproject.org/paste/X8FQzEXjGXQBTKAVLnDn4w
> 
> I have tested your patch and it resolves the issue described.
> I like not having to introduce a new list and lock.

Me too. This looks like the best of all proposed solutions.

> 
> Small note: I think you need to increase net->ipv6.rt6_stats->fib_rt_uncache
> when adding to the IPv6 uncached list from the xfrm code.

Xing, plaese incorporate the review and submit the patch.

Thanks!