linux-kernel - Re: [Patch] net: kill an RCU warning in inet_fill_link

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Message-ID: <1291224717.2856.1021.camel@edumazet-laptop>
Date:	Wed, 01 Dec 2010 18:31:57 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Graf <tgraf@...radead.org>
Cc:	Amerigo Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [Patch] net: kill an RCU warning in inet_fill_link_af()

Le mercredi 01 décembre 2010 à 12:18 -0500, Thomas Graf a écrit :
> On Wed, Dec 01, 2010 at 05:03:06PM +0100, Eric Dumazet wrote:
> > [PATCH net-next-2.6] net: kill an RCU warning in inet_fill_link_af()
> > 
> > commits 9f0f7272 (ipv4: AF_INET link address family) and cf7afbfeb8c
> > (rtnl: make link af-specific updates atomic) used incorrect
> > __in_dev_get_rcu() in RTNL protected contexts, triggering PROVE_RCU
> > warnings.
> > 
> > Switch to __in_dev_get_rtnl(), wich is more appropriate, since we hold
> > RTNL.
> > 
> > Based on a report and initial patch from Amerigo Wang.
> 
> RTNL is not held while dumping, it is only held for get and set, but we
> still hold rcu readlocks while dumping so there should be no asserts
> triggered. Thanks for fixing this.

Are you sure RTNL is not held while dumping ? 

Patrick did the change to hold RTNL while dumping too, 3.5 years ago.
Check commits 6313c1e0992fea, 1c2d670f3660e9103 ([RTNETLINK]: Hold
rtnl_mutex during netlink dump callbacks)

If this was the case (not holding RTNL), we should use
rcu_dereference(), not rtnl_dereference()



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