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From: Cong Wang <amwang@redhat.com>
To: Jay Vosburgh <fubar@us.ibm.com>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Neil Horman <nhorman@tuxdriver.com>,
	netdev@vger.kernel.org, Andy Gospodarek <gospo@redhat.com>,
	bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	bonding-devel@lists.sourceforge.net,
	Jeff Moyer <jmoyer@redhat.com>, Matt Mackall <mpm@selenic.com>,
	David Miller <davem@davemloft.net>
Subject: Re: [Bonding-devel] [v3 Patch 2/3] bridge: make bridge support netpoll
Date: Wed, 14 Apr 2010 16:11:02 +0800	[thread overview]
Message-ID: <4BC57896.9060707@redhat.com> (raw)
In-Reply-To: <8304.1271177567@death.nxdomain.ibm.com>

Jay Vosburgh wrote:
> Cong Wang <amwang@redhat.com> wrote:
> 
>> Stephen Hemminger wrote:
>>> On Mon, 12 Apr 2010 12:38:57 +0200
>>> Eric Dumazet <eric.dumazet@gmail.com> wrote:
>>>
>>>> Le lundi 12 avril 2010 à 18:37 +0800, Cong Wang a écrit :
>>>>> Stephen Hemminger wrote:
>>>>>> There is no protection on dev->priv_flags for SMP access.
>>>>>> It would better bit value in dev->state if you are using it as control flag.
>>>>>>
>>>>>> Then you could use 
>>>>>> 			if (unlikely(test_and_clear_bit(__IN_NETPOLL, &skb->dev->state)))
>>>>>> 				netpoll_send_skb(...)
>>>>>>
>>>>>>
>>>>> Hmm, I think we can't use ->state here, it is not for this kind of purpose,
>>>>> according to its comments.
>>>>>
>>>>> Also, I find other usages of IFF_XXX flags of ->priv_flags are also using
>>>>> &, | to set or clear the flags. So there must be some other things preventing
>>>>> the race...
>>>> Yes, its RTNL that protects priv_flags changes, hopefully...
>>>>
>>> The patch was not protecting priv_flags with RTNL.
>>> For example..
>>>
>>>
>>> @@ -308,7 +312,9 @@ static void netpoll_send_skb(struct netp
>>>  		     tries > 0; --tries) {
>>>  			if (__netif_tx_trylock(txq)) {
>>>  				if (!netif_tx_queue_stopped(txq)) {
>>> +					dev->priv_flags |= IFF_IN_NETPOLL;
>>>  					status = ops->ndo_start_xmit(skb, dev);
>>> +					dev->priv_flags &= ~IFF_IN_NETPOLL;
>>>  					if (status == NETDEV_TX_OK)
>>>  						txq_trans_update(txq);
>> Hmm, but I checked the bonding case (IFF_BONDING), it doesn't
>> hold rtnl_lock. Strange.
> 
> 	I looked, and there are a couple of cases in bonding that don't
> have RTNL for adjusting priv_flags (in bond_ab_arp_probe when no slaves
> are up, and a couple of cases in 802.3ad).  I think the solution there
> is to move bonding away from priv_flags for some of this (e.g., convert
> bonding to use a frame hook like bridge and macvlan, and greatly
> simplify skb_bond_should_drop), but that's a separate topic.
> 
> 	The majority of the cases, however, do hold RTNL.  Bonding
> generally doesn't have to acquire RTNL itself, since whatever called
> into bonding is holding it already.  For example, the slave add and
> remove paths (bond_enslave, bond_release) are called either via sysfs or
> ioctl, both of which acquire RTNL.  All of the set and clear operations
> for IFF_BONDING fall into this category; look at bonding_store_slaves
> for an example.
> 
> 	Bonding does acquire RTNL itself when performing failovers,
> e.g., bond_mii_monitor holds RTNL prior to calling bond_miimon_commit,
> which will change priv_flags.
> 

Thanks a lot for your reply!

You are right, I missed something.

Hmm, for bonding, RTNL lock is necessary because there are sysfs
interface and ioctl interface to change its configuration.

  parent reply	other threads:[~2010-04-14  8:11 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-04-08  6:18 [v3 Patch 1/3] netpoll: add generic support for bridge and bonding devices Amerigo Wang
2010-04-08  6:18 ` [v3 Patch 2/3] bridge: make bridge support netpoll Amerigo Wang
2010-04-08 15:37   ` Stephen Hemminger
2010-04-09  5:43     ` Cong Wang
2010-04-12 10:37     ` Cong Wang
2010-04-12 10:38       ` Eric Dumazet
2010-04-12 15:38         ` [Bonding-devel] " Stephen Hemminger
2010-04-13  8:57           ` Cong Wang
2010-04-13 16:52             ` Jay Vosburgh
2010-04-13 17:33               ` Stephen Hemminger
2010-04-14  8:16                 ` Cong Wang
2010-04-14  8:11               ` Cong Wang [this message]
2010-04-08  6:19 ` [v3 Patch 3/3] bonding: make bonding " Amerigo Wang

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