linux-kernel - Re: RTNL: assertion failed at net/ipv6/addrconf.c (1699)

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Date:	Tue, 02 Sep 2014 19:58:04 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Cong Wang <cwang@...pensource.com>
Cc:	Sabrina Dubroca <sd@...asysnail.net>,
	Tommi Rantala <tt.rantala@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, trinity@...r.kernel.org,
	Dave Jones <davej@...hat.com>
Subject: Re: RTNL: assertion failed at net/ipv6/addrconf.c (1699)

Hi Cong,

On Tue, Sep 2, 2014, at 18:50, Cong Wang wrote:
> On Fri, Aug 29, 2014 at 6:51 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> >
> > Also rtnl_lock and rcu_read_lock compose in that order, so we don't need
> > to change dev_get_by_flags, but as this is the only user it sure is
> > possible. RCU locked version is just easier composeable, so I wouldn't
> > touch that if needed in future, just also take rcu lock as before.
> 
> There is no point to keep RCU read lock if we have rtnl lock,
> I don't know why you don't want to change dev_get_by_flags(),
> it is pretty easy to do since it only has one caller.

I definitely don't have a problem cleaning this up in net-next. I wanted
a minimal patch for stable because I didn't check history where and when
additional users of dev_get_by_flags_rcu were removed.

> Even if you really need RCU in future, you are always welcome
> to bring it back when you do, sorry we should never be blocked by
> code NOT merged yet.
> 
> >
> > Also we should move ASSERT_RTNL checks from addrconf_join_solict to
> > ipv6_dev_mc_inc/dec.
> >
> 
> Make it another patch.

It is just one logical change, moving ASSERT_RTNLs to places where they
better catch invalid callstacks.

Bye,
Hannes
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