From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: Re: [Bonding-devel] [v3 Patch 2/3] bridge: make bridge support netpoll Date: Wed, 14 Apr 2010 16:11:02 +0800 Message-ID: <4BC57896.9060707@redhat.com> 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; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Stephen Hemminger , 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 Jay Vosburgh wrote: > Cong Wang wrote: >=20 >> Stephen Hemminger wrote: >>> On Mon, 12 Apr 2010 12:38:57 +0200 >>> Eric Dumazet wrote: >>> >>>> 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 c= ontrol flag. >>>>>> >>>>>> Then you could use=20 >>>>>> if (unlikely(test_and_clear_bit(__IN_NETPOLL, &skb->dev->stat= e))) >>>>>> netpoll_send_skb(...) >>>>>> >>>>>> >>>>> Hmm, I think we can't use ->state here, it is not for this kind o= f purpose, >>>>> according to its comments. >>>>> >>>>> Also, I find other usages of IFF_XXX flags of ->priv_flags are al= so using >>>>> &, | to set or clear the flags. So there must be some other thing= s 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 |=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 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.