netdev - Re: [PATCH ipsec,v2] net: xfrm_policy: fix device unregistration hang

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Message-ID: <20180213065505.n2jodesr5s32gcfo@gauss3.secunet.de>
Date:   Tue, 13 Feb 2018 07:55:05 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Eyal Birger <eyal.birger@...il.com>
CC:     <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <fw@...len.de>,
        <shmulik@...anetworks.com>, <shannon.nelson@...cle.com>
Subject: Re: [PATCH ipsec,v2] net: xfrm_policy: fix device unregistration hang

On Mon, Feb 12, 2018 at 08:58:28PM +0200, Eyal Birger 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.
> 
> 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 event.
> 
> Signed-off-by: Eyal Birger <eyal.birger@...il.com>

Please add a 'Fixes' tag, it is not so clear what introduced this bug.