From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [Bonding-devel] [v3 Patch 2/3] bridge: make bridge support netpoll Date: Tue, 13 Apr 2010 10:33:20 -0700 Message-ID: <20100413103320.11a2a4f7@nehalam> References: <20100408062234.4499.17042.sendpatchset@localhost.localdomain> <20100408062246.4499.5670.sendpatchset@localhost.localdomain> <20100408083710.2b61ee44@nehalam> <4BC2F7E2.7020309@redhat.com> <1271068737.16881.18.camel@edumazet-laptop> <20100412083842.26d71bda@nehalam> <4BC43214.6030009@redhat.com> <8304.1271177567@death.nxdomain.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Cong Wang , Eric Dumazet , Neil Horman , netdev@vger.kernel.org, Andy Gospodarek , bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, bonding-devel@lists.sourceforge.net, Jeff Moyer , Matt Mackall , David Miller To: Jay Vosburgh Return-path: In-Reply-To: <8304.1271177567@death.nxdomain.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, 13 Apr 2010 09:52:47 -0700 Jay Vosburgh wrote: > Cong Wang wrote: >=20 > >Stephen Hemminger wrote: > >> On Mon, 12 Apr 2010 12:38:57 +0200 > >> Eric Dumazet wrote: > >>=20 > >>> Le lundi 12 avril 2010 =C3=A0 18:37 +0800, Cong Wang a =C3=A9crit= : > >>>> 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=20 > >>>>> if (unlikely(test_and_clear_bit(__IN_NETPOLL, &skb->dev->sta= te))) > >>>>> 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 a= lso using > >>>> &, | to set or clear the flags. So there must be some other thin= gs preventing > >>>> the race... > >>> Yes, its RTNL that protects priv_flags changes, hopefully... > >>> > >>=20 > >> The patch was not protecting priv_flags with RTNL. > >> For example.. > >>=20 > >>=20 > >> @@ -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 |=3D IFF_IN_NETPOLL; > >> status =3D ops->ndo_start_xmit(skb, dev); > >> + dev->priv_flags &=3D ~IFF_IN_NETPOLL; > >> if (status =3D=3D NETDEV_TX_OK) > >> txq_trans_update(txq); > > > >Hmm, but I checked the bonding case (IFF_BONDING), it doesn't > >hold rtnl_lock. Strange. >=20 > 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 slav= es > are up, and a couple of cases in 802.3ad). I think the solution ther= e > is to move bonding away from priv_flags for some of this (e.g., conve= rt > bonding to use a frame hook like bridge and macvlan, and greatly > simplify skb_bond_should_drop), but that's a separate topic. >=20 > 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 operatio= ns > for IFF_BONDING fall into this category; look at bonding_store_slaves > for an example. >=20 > 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. >=20 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. --=20