From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe Koziolek Subject: Re: [PATCH] net/bonding: send arp in interval if no active slave Date: Wed, 2 Sep 2015 01:10:29 +0200 Message-ID: <55E63065.8070906@redknee.com> References: <1439828583-27325-1-git-send-email-jarod@redhat.com> <20150817165500.GA21512@vps.falico.eu> <55D215F7.3080905@redhat.com> <55D22E64.6020807@redknee.com> <2649.1439838866@famine> <55D2494F.3020800@redknee.com> <20150901154157.GY504@gospo.home.greyhouse.net> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Cc: Jay Vosburgh , Jarod Wilson , Veaceslav Falico , , To: Andy Gospodarek Return-path: In-Reply-To: <20150901154157.GY504@gospo.home.greyhouse.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Sep 01, 2015 at 05:41 PM +0200, Andy Gospodarek wrote: > On Mon, Aug 17, 2015 at 10:51:27PM +0200, Uwe Koziolek wrote: >> On Mon, Aug 17, 2015 at 09:14PM +0200, Jay Vosburgh wrote: >>> Uwe Koziolek wrote: >>> >>>> On2015-08-17 07:12 PM,Jarod Wilson wrote: >>>>> On 2015-08-17 12:55 PM, Veaceslav Falico wrote: >>>>>> On Mon, Aug 17, 2015 at 12:23:03PM -0400, Jarod Wilson wrote: >>>>>>> From: Uwe Koziolek >>>>>>> >>>>>>> With some very finicky switch hardware, active backup bonding can get >>>>>>> into >>>>>>> a situation where we play ping-pong between interfaces, trying to get >>>>>>> one >>>>>>> to come up as the active slave. There seems to be an issue with the >>>>>>> switch's arp replies either taking too long, or simply getting lost, >>>>>>> so we >>>>>>> wind up unable to get any interface up and active. Sometimes, the issue >>>>>>> sorts itself out after a while, sometimes it doesn't. >>>>>>> >>>>>>> Testing with num_grat_arp has proven fruitless, but sending an >>>>>>> additional >>>>>>> arp on curr_arp_slave if we're still in the arp_interval timeslice in >>>>>>> bond_ab_arp_probe(), has shown to produce 100% reliability in testing >>>>>>> with >>>>>>> this hardware combination. >>>>>> Sorry, I don't understand the logic of why it works, and what exactly >>>>>> are >>>>>> we fixiing here. >>>>>> >>>>>> It also breaks completely the logic for link state management in case >>>>>> of no >>>>>> current active slave for 2*arp_interval. >>>>>> >>>>>> Could you please elaborate what exactly is fixed here, and how it >>>>>> works? :) >>>>> I can either duplicate some information from the bug, or Uwe can, to >>>>> illustrate the exact nature of the problem. >>>>> >>>>>> p.s. num_grat_arp maybe could help? >>>>> That was my thought as well, but as I understand it, that route was >>>>> explored, and it didn't help any. I don't actually have a reproducer >>>>> setup of my own, unfortunately, so I'm kind of caught in the middle >>>>> here... >>>>> >>>>> Uwe, can you perhaps further enlighten us as to what num_grat_arp >>>>> settings were tried that didn't help? I'm still of the mind that if >>>>> num_grat_arp *didn't* help, we probably need to do something keyed off >>>>> num_grat_arp. >>>> The bonding slaves are connected to high available switches, each of the >>>> slaves is connected to a different switch. If the bond is starting, only >>>> the selected slave sends one arp-request. If a matching arp_response was >>>> received, this slave and the bond is going into state up, sending the >>>> gratitious arps... >>>> But if you got no arp reply the next slave was selected. >>>> With most of the newer switches, not overloaded, or with other software >>>> bugs, or with a single switch configuration, you would get a arp response >>>> on the first arp request. >>>> But in case of high availability configuration with non perfect switches >>>> like HP ProCurve 54xx, also with some Cisco models, you may not get a >>>> response on the first arp request. >>>> >>>> I have seen network snoops, there the switches are not responding to the >>>> first arp request on slave 1, the second arp request was sent on slave 2 >>>> but the response was received on slave one, and all following arp >>>> requests are anwsered on the wrong slave for a longer time. >>> Could you elaborate on the exact "high availability >>> configuration" here, including the model(s) of switch(es) involved? >>> >>> Is this some kind of race between the switch or switches >>> updating the forwarding tables and the bond flip flopping between the >>> slaves? E.g., source MAC from ARP sent on slave 1 is used to populate >>> the forwarding table, but (for whatever reason) there is no reply. ARP >>> on slave 2 is sent (using the same source MAC, unless you set >>> fail_over_mac), but forwarding tables still send that MAC to slave 1, so >>> reply is sent there. >> High availability: >> 2 managed switches with routing capabilities have an interconnect. >> One slave of a bonding interface is connected to the first switch, the >> second slave is connected to the other switch. >> The switch models are HP ProCurve 5406 and HP ProCurve 5412. As far as i >> remember also HP E 3500 and E 3800 are also >> affected, for the affected Cisco models I can't answer today. >> Affected single switch configurations was not seen. >> >> Yes, race conditions with delayed upgrades of the forwarding tables is a >> well matching explanation for the problem. >> >>>> The proposed change sents up to 3 arp requests on a down bond using the >>>> same slave, delayed by arp_interval. >>>> Using problematic switches i have seen the the arp response on the right >>>> slave at latest on the second arp request. So the bond is going into state >>>> up. >>>> >>>> How does it works: >>>> The bonds in up state are handled on the beginning of bond_ab_arp_probe >>>> procedure, the other part of this procedure is handling the slave change. >>>> The proposed change is bypassing the slave change for 2 additional calls >>>> of bond_ab_arp_probe. >>>> Now the retries are not only for an up bond available, they are also >>>> implemented for a down bond. >>> Does this delay failover or bringup on switches that are not >>> "problematic"? I.e., if arp_interval is, say, 1000 (1 second), will >>> this impact failover / recovery times? >>> >>> -J >> It depends. >> failover times are not impacted, this is handled different. >> Only the transition from a down bonding interface (bond and all slaves are >> down) to the state up can be increased by up to 2 times arp_interval, >> If the selected interface did not came up .If well working switches are >> used, and everything other is also ok, there are no impacts. > So I'm not a huge fan of workarounds like these, but I also understand > from a practical standpoint that this is useful. My only issue with the > patch would be to please include a small comment (1-2 lines) in the code > that describes the behavior. I know we have the changelog entries for > this, but I would feel better about having an exception like this in the > code for those reading it and wondering: > > "Why would we wait 2 intervals before failing over to the next interface > when there are no active interfaces?" > diff -up a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c --- a/drivers/net/bonding/bond_main.c 2015-08-30 20:34:09.000000000 +0200 +++ b/drivers/net/bonding/bond_main.c 2015-09-02 00:39:10.000298202 +0200 @@ -2795,6 +2795,16 @@ static bool bond_ab_arp_probe(struct bon return should_notify_rtnl; } + /* sometimes the forwarding tables of the switches are not updated fast enough + * the first arp response after a slave change is received on the wrong slave. + * the arp requests will be retried 2 times on the same slave + */ + + if (bond_time_in_interval(bond, curr_arp_slave->last_link_up, 2)) { + bond_arp_send_all(bond, curr_arp_slave); + return should_notify_rtnl; + } + bond_set_slave_inactive_flags(curr_arp_slave, BOND_SLAVE_NOTIFY_LATER); bond_for_each_slave_rcu(bond, slave, iter) { >>>> The num_grat_arp has no chance to solve the problem. The num_grat_arp is >>>> only used, if a different slave is going active. >>>> But in our case, the bonding slaves are not going into the state active >>>> for a longer time. >>>>>>> [jarod: manufacturing of changelog] >>>>>>> CC: Jay Vosburgh >>>>>>> CC: Veaceslav Falico >>>>>>> CC: Andy Gospodarek >>>>>>> CC: netdev@vger.kernel.org >>>>>>> Signed-off-by: Uwe Koziolek >>>>>>> Signed-off-by: Jarod Wilson >>>>>>> --- >>>>>>> drivers/net/bonding/bond_main.c | 5 +++++ >>>>>>> 1 file changed, 5 insertions(+) >>>>>>> >>>>>>> diff --git a/drivers/net/bonding/bond_main.c >>>>>>> b/drivers/net/bonding/bond_main.c >>>>>>> index 0c627b4..60b9483 100644 >>>>>>> --- a/drivers/net/bonding/bond_main.c >>>>>>> +++ b/drivers/net/bonding/bond_main.c >>>>>>> @@ -2794,6 +2794,11 @@ static bool bond_ab_arp_probe(struct bonding >>>>>>> *bond) >>>>>>> return should_notify_rtnl; >>>>>>> } >>>>>>> >>>>>>> + if (bond_time_in_interval(bond, curr_arp_slave->last_link_up, 2)) >>>>>>> { >>>>>>> + bond_arp_send_all(bond, curr_arp_slave); >>>>>>> + return should_notify_rtnl; >>>>>>> + } >>>>>>> + >>>>>>> bond_set_slave_inactive_flags(curr_arp_slave, >>>>>>> BOND_SLAVE_NOTIFY_LATER); >>>>>>> >>>>>>> bond_for_each_slave_rcu(bond, slave, iter) { >>>>>>> -- >>>>>>> 1.8.3.1 >>> --- >>> -Jay Vosburgh, jay.vosburgh@canonical.com