On Tue, 13 Apr 2010 09:52:47 -0700 Jay Vosburgh <fubar@xxxxxxxxxx> 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. > All this was related to netpoll. And netpoll processing often needs to occur in hard IRQ context. Therefor netpoll stuff and RTNL (which is a mutex), really don't mix well. Keep RTNL for what it was meant for network reconfiguration. Don't turn it into a network special BKL. -- _______________________________________________ Bridge mailing list Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/bridge