netdev - Re: [PATCH net] tipc: change to use register_pernet

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Message-Id: <20190622.165414.71029280359569399.davem@davemloft.net>
Date:   Sat, 22 Jun 2019 16:54:14 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, jon.maloy@...csson.com,
        ying.xue@...driver.com, tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net] tipc: change to use register_pernet_device

From: Xin Long <lucien.xin@...il.com>
Date: Thu, 20 Jun 2019 18:39:28 +0800

> This patch is to fix a dst defcnt leak, which can be reproduced by doing:
> 
>   # ip net a c; ip net a s; modprobe tipc
>   # ip net e s ip l a n eth1 type veth peer n eth1 netns c
>   # ip net e c ip l s lo up; ip net e c ip l s eth1 up
>   # ip net e s ip l s lo up; ip net e s ip l s eth1 up
>   # ip net e c ip a a 1.1.1.2/8 dev eth1
>   # ip net e s ip a a 1.1.1.1/8 dev eth1
>   # ip net e c tipc b e m udp n u1 localip 1.1.1.2
>   # ip net e s tipc b e m udp n u1 localip 1.1.1.1
>   # ip net d c; ip net d s; rmmod tipc
> 
> and it will get stuck and keep logging the error:
> 
>   unregister_netdevice: waiting for lo to become free. Usage count = 1
> 
> The cause is that a dst is held by the udp sock's sk_rx_dst set on udp rx
> path with udp_early_demux == 1, and this dst (eventually holding lo dev)
> can't be released as bearer's removal in tipc pernet .exit happens after
> lo dev's removal, default_device pernet .exit.
> 
>  "There are two distinct types of pernet_operations recognized: subsys and
>   device.  At creation all subsys init functions are called before device
>   init functions, and at destruction all device exit functions are called
>   before subsys exit function."
> 
> So by calling register_pernet_device instead to register tipc_net_ops, the
> pernet .exit() will be invoked earlier than loopback dev's removal when a
> netns is being destroyed, as fou/gue does.
> 
> Note that vxlan and geneve udp tunnels don't have this issue, as the udp
> sock is released in their device ndo_stop().
> 
> This fix is also necessary for tipc dst_cache, which will hold dsts on tx
> path and I will introduce in my next patch.
> 
> Reported-by: Li Shuang <shuali@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Applied.