netdev - Re: [PATCH v2] ipv6: Don't depend on per socket memory for neighbour discovery messages

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Date:	Tue, 3 Sep 2013 19:23:48 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org, Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH v2] ipv6: Don't depend on per socket memory for neighbour
 discovery messages

On 09/03/13 at 12:03pm, Stephen Warren wrote:
> On 09/03/2013 11:51 AM, Eric Dumazet wrote:
> > On Tue, 2013-09-03 at 11:42 -0600, Stephen Warren wrote:
> > 
> >> I don't see any extra messages from PROVE_LOCKING related to networking.
> >> There is a single extra message from inside the audio driver, but that's
> >> not networking-related at all.
> > 
> > LOCKDEP is automatically disabled at first splat.
> > 
> > Please try a kernel without audio driver ;)
> 
> Ah, OK. Now I do see something from ipv6:
> 
> > [   25.327622] 
> > [   25.329142] =============================================
> > [   25.334533] [ INFO: possible recursive locking detected ]
> > [   25.339927] 3.11.0-rc7-next-20130830-00024-g209b4d8-dirty #17 Not tainted
> > [   25.346705] ---------------------------------------------
> > [   25.352095] login/704 is trying to acquire lock:
> > [   25.356705]  (&ndev->lock){++--..}, at: [<c049be24>] ipv6_chk_mcast_addr+0x5c/0x200
> > [   25.364405] 
> > [   25.364405] but task is already holding lock:
> > [   25.370230]  (&ndev->lock){++--..}, at: [<c0480eb4>] addrconf_rs_timer+0x18/0x134

Real deadlock, we should not hold idev->lock for ndisc_send_rs(), we
should drop the lock beforehand I guess. We also don't hold idev->lock
if we send out the RS via addrconf_dad_completed().

I'm confused why lockdep would only trigger after my patch, the
deadlock is unrelated.

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