netdev - Re: Possible deadlock in ipv6?

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Date:	Wed, 06 Jun 2012 17:58:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Possible deadlock in ipv6?

On Wed, 2012-06-06 at 17:53 +0200, Eric Dumazet wrote:
> On Wed, 2012-06-06 at 18:49 +0400, Vladimir Davydov wrote:
> > I'm not familiar with the linux net subsystem, so I would appreciate if 
> > someone could clarify if the following call chain is possible:
> > 
> > addrconf_ifdown() calls neigh_ifdown(nd_tbl) which locks nd_tbl.lock for 
> > writing and calls
> > 
> >      pneigh_ifdown
> >      pndisc_destructor
> >      ipv6_dev_mc_dec
> >      __ipv6_dev_mc_dec
> >      igmp6_group_dropped
> >      igmp6_leave_group
> >      igmp6_send
> >      icmp6_dst_alloc
> >      ip6_neigh_lookup
> >      neigh_create
> > 
> > and neigh_create() locks nd_tbl.lock for writing again resulting in a 
> > deadlock.
> 
> It seems a deadlock is possible indeed, good catch !
> 
> 

And it seems this neigh_down() can be removed, its called later
(after dev->ip6_ptr is cleared)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8f6411c..62c4c00 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2750,7 +2750,6 @@ static int addrconf_ifdown(struct net_device *dev, int how)
 	ASSERT_RTNL();
 
 	rt6_ifdown(net, dev);
-	neigh_ifdown(&nd_tbl, dev);
 
 	idev = __in6_dev_get(dev);
 	if (idev == NULL)


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