Jay Vosburgh wrote:
> Cong Wang <amwang@xxxxxxxxxx> wrote:
>
>> Stephen Hemminger wrote:
>>> On Mon, 12 Apr 2010 12:38:57 +0200
>>> Eric Dumazet <eric.dumazet@xxxxxxxxx> 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.
_______________________________________________
Bridge mailing list
Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/bridge
