From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ding Tianhong Subject: Re: [PATCH v2 net-next 2/3] bonding: fix __get_first_agg RCU usage Date: Thu, 9 Jan 2014 19:58:17 +0800 Message-ID: <52CE8ED9.60609@huawei.com> References: <1389266425-28365-1-git-send-email-vfalico@redhat.com> <1389266425-28365-3-git-send-email-vfalico@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Jay Vosburgh , Andy Gospodarek To: Veaceslav Falico , Return-path: Received: from szxga01-in.huawei.com ([119.145.14.64]:17051 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750990AbaAIL6n (ORCPT ); Thu, 9 Jan 2014 06:58:43 -0500 In-Reply-To: <1389266425-28365-3-git-send-email-vfalico@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2014/1/9 19:20, Veaceslav Falico wrote: > Currently, the RCU read lock usage is just wrong - it gets the slave struct > under RCU and continues to use it when RCU lock is released. > > However, it's still safe to do this cause we didn't need the > rcu_read_lock() initially - all of the __get_first_agg() callers are either > holding RCU read lock or the RTNL lock, so that we can't sync while in it. > > So, remove the useless rcu locking and add a comment. > > Fixes: be79bd048 ("bonding: add RCU for bond_3ad_state_machine_handler()") > CC: dingtianhong@huawei.com > CC: Jay Vosburgh > CC: Andy Gospodarek > Signed-off-by: Veaceslav Falico > --- > > Notes: > v1 -> v2: > Don't use RCU primitives as we can hold RTNL. > > drivers/net/bonding/bond_3ad.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c > index cf5fab8..d2782c8 100644 > --- a/drivers/net/bonding/bond_3ad.c > +++ b/drivers/net/bonding/bond_3ad.c > @@ -143,6 +143,7 @@ static inline struct bonding *__get_bond_by_port(struct port *port) > * > * Return the aggregator of the first slave in @bond, or %NULL if it can't be > * found. > + * The caller must either hold RCU or RTNL lock. > */ > static inline struct aggregator *__get_first_agg(struct port *port) > { > @@ -153,9 +154,7 @@ static inline struct aggregator *__get_first_agg(struct port *port) > if (bond == NULL) > return NULL; > > - rcu_read_lock(); > - first_slave = bond_first_slave_rcu(bond); > - rcu_read_unlock(); > + first_slave = bond_first_slave(bond); > > return first_slave ? &(SLAVE_AD_INFO(first_slave).aggregator) : NULL; > } > Hi, Veaceslav: Do you mean the bond_first_slave is safe in rcu_read_xxlock()? #define bond_first_slave(bond) \ (bond_has_slaves(bond) ? \ netdev_adjacent_get_private(bond_slave_list(bond)->next) : \ NULL) Regards Ding