Messages in this thread Patch in this message | | | Subject | Re: [PATCH] net/bonding: send arp in interval if no active slave | From | Uwe Koziolek <> | Date | Fri, 4 Sep 2015 13:04:38 +0200 |
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Am 03.09.2015 um 17:05 schrieb Jay Vosburgh: > Uwe Koziolek <uwe.koziolek@redknee.com> wrote: > >> 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 <uwe.koziolek@redknee.com> 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 <uwe.koziolek@redknee.com> >>>>>>>>> >>>>>>>>> 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; >> + } >> + > > I probably should have asked this in the beginning, but at what > range of arp_interval values does the problem manifest? If it's a race > condition with the switch update, I'd expect that only very small > arp_interval values would be affected. > > Also, your proposed comment wraps past 80 columns. > > -J > Only 500 msecs arp interval is used, no other values are checked. Wraps in patch are now removed.
diff -up ./drivers/net/bonding/bond_main.c.orig ./drivers/net/bonding/bond_main.c --- ./drivers/net/bonding/bond_main.c.orig 2015-08-30 20:34:09.000000000 +0200 +++ ./drivers/net/bonding/bond_main.c 2015-09-04 11:59:05.755897182 +0200 @@ -2795,6 +2795,17 @@ 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) { > >> 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 <j.vosburgh@gmail.com> >>>>>>>>> CC: Veaceslav Falico <vfalico@gmail.com> >>>>>>>>> CC: Andy Gospodarek <gospo@cumulusnetworks.com> >>>>>>>>> CC: netdev@vger.kernel.org >>>>>>>>> Signed-off-by: Uwe Koziolek <uwe.koziolek@redknee.com> >>>>>>>>> Signed-off-by: Jarod Wilson <jarod@redhat.com> >>>>>>>>> --- >>>>>>>>> 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 >
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