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Date: Mon, 28 Oct 2013 02:34:28 +0100 From: Veaceslav Falico <vfalico@...hat.com> To: Ding Tianhong <dingtianhong@...wei.com> Cc: Jay Vosburgh <fubar@...ibm.com>, Andy Gospodarek <andy@...yhouse.net>, "David S. Miller" <davem@...emloft.net>, Nikolay Aleksandrov <nikolay@...hat.com>, Netdev <netdev@...r.kernel.org> Subject: Re: [PATCH net-next v2 0/5] bonding: patchset for rcu use in bonding On Mon, Oct 28, 2013 at 09:15:52AM +0800, Ding Tianhong wrote: >On 2013/10/28 6:53, Veaceslav Falico wrote: >> On Thu, Oct 24, 2013 at 11:08:35AM +0800, Ding Tianhong wrote: >>> Hi: >>> >>> The slave list will add and del by bond_master_upper_dev_link() and bond_upper_dev_unlink(), >>> which will call call_netdevice_notifiers(), even it is safe to call it in write bond lock now, >>> but we can't sure that whether it is safe later, because other drivers may deal NETDEV_CHANGEUPPER >>> in sleep way, so I didn't admit move the bond_upper_dev_unlink() in write bond lock. >>> >>> now the bond_for_each_slave only protect by rtnl_lock(), maybe use bond_for_each_slave_rcu is a good >>> way to protect slave list for bond, but as a system slow path, it is no need to transform bond_for_each_slave() >>> to bond_for_each_slave_rcu() in slow path, so in the patchset, I will remove the unused read bond lock >>> for monitor function, maybe it is a better way, I will wait to accept any relay for it. >>> >>> Thanks for the Veaceslav Falico opinion. >>> >>> v2: add and modify commit for patchset and patch, it will be the first step for the whole patchset. >>> >>> Ding Tianhong (5): >>> bonding: remove bond read lock for bond_mii_monitor() >>> bonding: remove bond read lock for bond_alb_monitor() >>> bonding: remove bond read lock for bond_loadbalance_arp_mon() >>> bonding: remove bond read lock for bond_activebackup_arp_mon() >> >> This patch introduces a regression by boot-test with active backup mode: >> >> bond_activebackup_arp_mon() is already not holding the bond->lock, however >> it might call bond_change_active_slave(), which does (in case of new_active): >> >> 912 write_unlock_bh(&bond->curr_slave_lock); >> 913 read_unlock(&bond->lock); >> 914 915 call_netdevice_notifiers(NETDEV_BONDING_FAILOVER, bond->dev); >> 916 if (should_notify_peers) >> 917 call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, >> 918 bond->dev); >> 919 920 read_lock(&bond->lock); >> 921 write_lock_bh(&bond->curr_slave_lock); >> >> so it drops the bond->lock (which wasn't taken previously), and then takes >> it (without anyone dropping it afterwards). >> >> I don't know how to fix it - cause a lot of other callers already take it, >> and we can't just drop them (we'd race), and we can't remove it here (cause >> we can't call notifiers while atomic). >> >> Which begs the question - was this patchset tested at all? >> >> [ 21.796823] ===================================== >> [ 21.796823] [ BUG: bad unlock balance detected! ] ... snip ... > >Hi David: >yes, exactly I miss it and make a mistake, the bond_select_active_slave is still have the protect problem and >need to be processed, I miss it, sorry, I will send a patch to fix the bug soon. > >Hi Veaceslav: >sorry about the commit, I will pay more attention to the commit and test, thanks for your advise and report the bug, >I have to admin that I was too careless. I'll ask you once again, even though it seems that my NACK doesn't block the patchset - try writing commit messages that actually describe why and how you do it. It's, actually, not only for the reviewers - it's also really good for you - cause while writing the commit log you also understand a lot more what are you doing, and might spot some corner cases (like this one). Sorry for being negative, however it costs me *much* more time to review patches without proper commit messages. I've done it once, twice, several times more - but that's it, I refuse to spend my time on your skipped homework. It might also help to split patches into really small steps - as in - do only one thing at a time, and describe it. This will help evade bugs *a lot*. It also helps people who'll bisect it, bugfix it and review it - because every patch will be a small, well-documented change, instead of a chunk of code with a description 'lets remove bond->lock'. Thank you and hope that helps. > > > > >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe netdev" in >>> the body of a message to majordomo@...r.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> . >> > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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