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

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Date:	Fri, 29 Mar 2013 15:39:39 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	paulmck@...ux.vnet.ibm.com
Cc:	eric.dumazet@...il.com, jpirko@...hat.com, rostedt@...dmis.org,
	andy@...yhouse.net, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, nicolas.2p.debian@...il.com,
	tglx@...utronix.de, streeter@...hat.com, stephen@...workplumber.org
Subject: Re: [PATCH] net: add a synchronize_net() in
 netdev_rx_handler_unregister()

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Date: Fri, 29 Mar 2013 12:20:11 -0700

> On Fri, Mar 29, 2013 at 06:01:22AM -0700, Eric Dumazet wrote:
>> [PATCH] net: add a synchronize_net() in netdev_rx_handler_unregister()
>> 
>> commit 35d48903e97819 (bonding: fix rx_handler locking) added a race
>> in bonding driver, reported by Steven Rostedt who did a very good
>> diagnosis :
 ...
>> We can fix bug this in two ways. First is adding a test in
>> bond_handle_frame() and others to check if rx_handler_data is NULL.
>> 
>> A second way is adding a synchronize_net() in
>> netdev_rx_handler_unregister() to make sure that a rcu protected reader
>> has the guarantee to see a non NULL rx_handler_data.
>> 
>> The second way is better as it avoids an extra test in fast path.
>> 
>> Reported-by: Steven Rostedt <rostedt@...dmis.org>
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> Cc: Jiri Pirko <jpirko@...hat.com>
>> Cc: Paul E. McKenney <paulmck@...ibm.com>
> 
> Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> With kudos to Steven Rostedt for his analogy between RCU and
> Schrödinger's cat.  ;-)

Applied and queued up for -stable, thanks Everyone.
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