From: Benjamin Poirier <bpoirier@suse.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: netdev@vger.kernel.org, Pablo Neira Ayuso <pablo@netfilter.org>,
Patrick McHardy <kaber@trash.net>,
"David S. Miller" <davem@davemloft.net>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Frysinger <vapier@gentoo.org>, Arun Sharma <asharma@fb.com>,
netfilter-devel@vger.kernel.org, netfilter@vger.kernel.org,
coreteam@netfilter.org, linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH RFC 1/2] netfilter: conntrack: remove RCU usage in conntrack notifier
Date: Fri, 27 Apr 2012 16:14:59 -0400 [thread overview]
Message-ID: <20120427201459.GA31254@d2.synalogic.ca> (raw)
In-Reply-To: <1335553131.2775.252.camel@edumazet-glaptop>
On 2012/04/27 20:58, Eric Dumazet wrote:
> On Fri, 2012-04-27 at 14:28 -0400, Benjamin Poirier wrote:
> > I think that the rcu usage in this code is pointless. It should either be
> > removed or, if it was intended to protect against something, it ought to make
> > that clear.
> >
> > 1) The code does not make use of the deferred deletion/wait for completion rcu
> > api (ie. synchronize_rcu(), call_rcu()).
> > 2) It does not benefit from the barriers implied by the rcu primitives used.
> > The code deals with callback pointers. There's no need to order writes to the
> > function code (!) before writes to the function pointers here.
> > ---
>
> At a first glance, this seems pretty wrong.
>
> code can disappear under you, thats for sure.
>
> CONFIG_NF_CT_NETLINK=m
>
> hint : module unload contains an rcu barrier.
>
Thank you Eric. I had indeed failed to consider module load/unload
cases, which are effectively "writes to function code".
prev parent reply other threads:[~2012-04-27 20:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-27 18:28 [PATCH RFC 1/2] netfilter: conntrack: remove RCU usage in conntrack notifier Benjamin Poirier
2012-04-27 18:28 ` [PATCH RFC 2/2] netfilter: conntrack: replace mutex with cmpxchg Benjamin Poirier
2012-05-02 0:51 ` Pablo Neira Ayuso
2012-04-27 18:58 ` [PATCH RFC 1/2] netfilter: conntrack: remove RCU usage in conntrack notifier Eric Dumazet
2012-04-27 20:14 ` Benjamin Poirier [this message]
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