linux-kernel - Re: [PATCH] net: add a synchronize_net() in netdev_rx_handler

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Message-ID: <5155AF24.3090305@redhat.com>
Date:	Fri, 29 Mar 2013 16:11:32 +0100
From:	Ivan Vecera <ivecera@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jiri Pirko <jpirko@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andy Gospodarek <andy@...yhouse.net>,
	"David S. Miller" <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Guy Streeter <streeter@...hat.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>, stephen@...workplumber.org
Subject: Re: [PATCH] net: add a synchronize_net() in netdev_rx_handler_unregister()

On 03/29/2013 02:01 PM, Eric Dumazet wrote:
>> CPU0 will see rx_handler set and yet, rx_handler_data nulled. Write
>> >barrier in rcu_assign_pointer() might prevent this reorder from happening.
>> >Therefore I suggest:
>> >
>> >diff --git a/net/core/dev.c b/net/core/dev.c
>> >index 0caa38e..c16b829 100644
>> >--- a/net/core/dev.c
>> >+++ b/net/core/dev.c
>> >@@ -3332,8 +3332,8 @@ void netdev_rx_handler_unregister(struct net_device *dev)
>> >  {
>> >
>> >  	ASSERT_RTNL();
>> >-	RCU_INIT_POINTER(dev->rx_handler, NULL);
>> >-	RCU_INIT_POINTER(dev->rx_handler_data, NULL);
>> >+	rcu_assign_pointer(dev->rx_handler, NULL);
>> >+	rcu_assign_pointer(dev->rx_handler_data, NULL);
>> >  }
>> >  EXPORT_SYMBOL_GPL(netdev_rx_handler_unregister);
>> >
>> >
> Nope this changes nothing at all.
Erik, why doesn't help the write barrier between the assignments. It 
should guarantee their orders... or not?

Thanks,
Ivan
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