netdev - Re: neigh_params_release() usage in net/ipv6/addrconf.c

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Message-ID: <4A0F3B0F.2070209@gmail.com>
Date:	Sun, 17 May 2009 00:15:43 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Chase Douglas <chasedouglas.lists@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: neigh_params_release() usage in net/ipv6/addrconf.c

Chase Douglas wrote, On 05/15/2009 06:33 PM:

> I'm debugging an issue I'm seeing when I use vlan with IPv6 support.  
> After bringing up the device, I'm unable to bring it down and  
> unregister it. I put some debug statements around dev_hold() and  
> dev_put() to see what was going on:
> 
> dev_hold() called on lo.2, new refcnt: 1 (net/core/dev.c:4162)
> dev_hold() called on lo.2, new refcnt: 2 (net/core/neighbour.c:1357)
> dev_hold() called on lo.2, new refcnt: 3 (net/ipv4/devinet.c:178)
> dev_hold() called on lo.2, new refcnt: 4 (net/core/neighbour.c:1357)
> dev_hold() called on lo.2, new refcnt: 5 (net/8021q/vlan.c:266)
> dev_hold() called on lo.2, new refcnt: 6 (net/core/link_watch.c:219)
> dev_put()  called on lo.2, new refcnt: 5 (net/core/link_watch.c:191)
> dev_hold() called on lo.2, new refcnt: 6 (net/core/dev.c:684)
> dev_put()  called on lo.2, new refcnt: 5 (net/ipv4/fib_semantics.c:149)
> dev_hold() called on lo.2, new refcnt: 6 (net/core/dev.c:684)
> dev_hold() called on lo.2, new refcnt: 7 (net/ipv4/fib_frontend.c:173)
> dev_put()  called on lo.2, new refcnt: 6 (net/ipv4/route.c:2453)
> dev_put()  called on lo.2, new refcnt: 5 (net/ipv4/fib_semantics.c:149)
> dev_put()  called on lo.2, new refcnt: 4 (net/core/neighbour.c:1393)
> dev_put()  called on lo.2, new refcnt: 3 (net/ipv4/devinet.c:151)
> dev_put()  called on lo.2, new refcnt: 2 (net/core/dev.c:4010)
> dev_put()  called on lo.2, new refcnt: 1 (net/8021q/vlan.c:182)
> unregister_netdevice: waiting for lo.2 to become free. Usage count = 2
> 
> The fourth dev_hold() is in neigh_parms_alloc(), called by  
> ipv6_add_dev(). The only place I see neigh_parms_release() called in  
> addrconf.c is if ipv6_add_dev() fails later on, or when taking the  
> device down in addrconf_ifdown(). Unfortunately, when I bring the vlan  
> dev down I never see addrconf_ifdown() called with the how parameter  
> set to 1, which is the only instance where neigh_parms_release() would  
> be called.

You write about ipv6, but the log is ipv4 only or I miss something.
Anyway, it seems you do this vlan on the loopback. If so, there is:

         if ((dev->flags & IFF_LOOPBACK) && how == 1)
                 how = 0;

at least before 2.6.29 kernels, and vlans copy most of the flags.
Otherwise, how == 1 should work OK.

> PS: I am running my tests using a slightly modified SLES 11 kernel. I  

Generally, it's better to give the kernel number, because everybody
uses Debian here. ...Not! ;-)

Jarek P.
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