netdev - Re: Possible deadlock in ipv6?

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Date:	Wed, 06 Jun 2012 19:02:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vladimir Davydov <VDavydov@...allels.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Possible deadlock in ipv6?

On Wed, 2012-06-06 at 20:01 +0400, Vladimir Davydov wrote:
> On Jun 6, 2012, at 7:58 PM, Eric Dumazet wrote:
> 
> > 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)
> > 
> 
> BTW, commit d1ed113f1669390da9898da3beddcc058d938587 did exactly the same, but it was reverted along with a bundle of other commits by 73a8bd74e2618990dbb218c3d82f53e60acd9af0.

Yes, but the revert was a 'revert a serie', while this particular patch
seems fine, especially if fixing a deadlock ;)




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