From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ding Tianhong Subject: Re: [PATCH v3 net-next 2/3] bonding: fix __get_first_agg RCU usage Date: Fri, 10 Jan 2014 18:43:41 +0800 Message-ID: <52CFCEDD.6030202@huawei.com> References: <1389345523-5497-1-git-send-email-vfalico@redhat.com> <1389345523-5497-3-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 szxga03-in.huawei.com ([119.145.14.66]:30694 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751148AbaAJKnx (ORCPT ); Fri, 10 Jan 2014 05:43:53 -0500 In-Reply-To: <1389345523-5497-3-git-send-email-vfalico@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2014/1/10 17:18, 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: > v2 -> v3: > Use the rcu primitives. > > v1 -> v2: > Don't use RCU primitives as we can hold RTNL. > > drivers/net/bonding/bond_3ad.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c > index 9ff55eb..27dac0e 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 hold RCU 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(); > I am afraid the lockdep check will calling some warming: bond_3ad_unbind_slave -> __get_first_agg -> bond_first_slave_rcu -> netdev_lower_get_first_private_rcu -> list_first_or_null_rcu but the bond_3ad_unbind_slave is not in RCU. Regards Ding > return first_slave ? &(SLAVE_AD_INFO(first_slave).aggregator) : NULL; > } >