[corosync] Corosync 1.3.x/1.4.x: Random redundant ring instabilities

Jerome Flesch jerome.flesch at netasq.com
Mon Jun 11 13:47:45 GMT 2012

I think you misunderstood me: We currently have 3 problems. The first 
one is the secondary ring going down and up all the time. The 2 others 
look really similar to https://bugzilla.redhat.com/show_bug.cgi?id=820821 .

We can reproduce the first one easily, and this is why I have been able 
to make a patch for it. However, 
https://bugzilla.redhat.com/show_bug.cgi?id=820821 is really hard for us 
to reproduce (or was ... I just saw your update on the bug report :). By 
really hard I mean that it occurred only on some of our customers' 
clusters and it is very rare. In other words, it happens at the worst 
place possible to debug it. This is why I wanted to use CTS to try to 
reproduce it.

Now that you have found what is causing the bug #820821, I will be able 
to make sure easily that we are affected by the very same bug. I'll also 
be able to test your patch :). I'll keep you updated on the results.

Thank you very much for your work.

By the way, I still think updating cts/README would be a good idea. For 
instance, it would allow me to run these tests on FreeBSD and our 
systems each time we switch to a new version a Corosync.

On 11.06.2012 09:35, Jan Friesse wrote:
> Jerome,
> you really don't need to install CTS to reproduce BZ#820821, because 
> as you wrote, you are able to reproduce by yourself. So if you can add 
> information to that BZ HOW you would able to reproduce it and/or find 
> out different (maybe more reliable reproducer) it would be great.
> Honza
> Jerome FLESCH napsal(a):
>> I've had a look at the bug report 
>> https://bugzilla.redhat.com/show_bug.cgi?id=820821 . If I understand 
>> it correctly, the only known way to reproduce this bug at the moment 
>> is to run CTS until it fails ? This bug is a major issue for us, so I 
>> would like to try to reproduce it on my end. However I haven't been 
>> able to run CTS yet. I've read 
>> https://github.com/corosync/corosync/tree/master/cts#readme but it 
>> seems obsolete (I can't find corolab.py anywhere in the repo). Also 
>> CTS seems to be tied in some way to Pacemaker ?
>> Could you please give some short instructions on how to run CTS, or 
>> better yet, update cts/README ?
>> ----- Mail original -----
>> De: "Jan Friesse"<jfriesse at redhat.com>
>> À: "Jerome FLESCH"<jerome.flesch at netasq.com>
>> Cc: discuss at corosync.org, "Christophe 
>> CARRE"<christophe.carre at netasq.com>, "Thomas 
>> MONTAGNE"<thomas.montagne at netasq.com>, 
>> "nicolas"<nicolas.dumont at netasq.com>
>> Envoyé: Jeudi 7 Juin 2012 11:04:04
>> Objet: Re: [corosync] Corosync 1.3.x/1.4.x: Random redundant ring 
>> instabilities
>> Jerome,
>> I believe first and second behavior is same as described in
>> https://bugzilla.redhat.com/show_bug.cgi?id=820821 by Andrew. I'm not
>> yet entirely sure WHY is happening.
>> Third one, flushing, is very important. Without flush, buffer may start
>> to overload and it causes really bad behavior (there was BZ with this
>> problem).
>> I would like Steve to review your patch, but for me it looks like ok.
>> Regards,
>>     Honza
>> Jerome FLESCH napsal(a):
>>> Hello,
>>> When upgrading from Corosync 1.2.8 to Corosync 1.4.2/1.4.3, some 
>>> nasty bugs appeared on our clusters. I observed the following bad 
>>> behaviors:
>>> 1) A process connected to Corosync with CPG wasn't correctly 
>>> informed that there are other processes connected on other 
>>> processors. It also didn't get their messages
>>> 2) A process sending messages with CPG never received copies of its 
>>> messages
>>> 3) 1 ring out of 2 went up/down quite often
>>> The behaviors 1 and 2 are very hard for us to reproduce, but we are 
>>> able to get the behavior 3 quite easily.
>>> The simplest setup we found to get it is the following:
>>> - 2 VirtualBox VMs, connected by 2 network interfaces (vboxnet0, 
>>> vboxnet1 ; one for each ring)
>>> - OS: Linux (Debian stable)
>>> - On one of the VMs, a test program sending some CPG messages (see 
>>> the script "test_corosync.sh" joined to this mail for example)
>>> Here are the Corosync logs we get when we do this setup:
>>> Jun 06 16:23:40 corosync [TOTEM ] A processor joined or left the 
>>> membership and a new membership was formed.
>>> Jun 06 16:23:40 corosync [CPG   ] chosen downlist: sender r(0) 
>>> ip( r(1) ip( ; members(old:1 left:0)
>>> Jun 06 16:23:40 corosync [MAIN  ] Completed service synchronization, 
>>> ready to provide service.
>>> Jun 06 16:24:37 corosync [TOTEM ] Marking ringid 1 interface 
>>> Jun 06 16:24:38 corosync [TOTEM ] Automatically recovered ring 1
>>> Jun 06 16:25:33 corosync [TOTEM ] Marking ringid 1 interface 
>>> Jun 06 16:25:34 corosync [TOTEM ] Automatically recovered ring 1
>>> Jun 06 16:26:35 corosync [TOTEM ] Marking ringid 1 interface 
>>> Jun 06 16:26:36 corosync [TOTEM ] Automatically recovered ring 1
>>> (...)
>>> The second ring goes down about every 2 minutes and automatically 
>>> back up right after.
>>> We spent some times looking for the commit that introduced this bug, 
>>> and it appears it's due the following one:
>>> Corosync 1.3.3 ->   1.3.4: e27a58d93d0d3795beb550f87b660c9c04f11386
>>> Corosync 1.4.1 ->   1.4.2: be608c050247e5f9c8266b8a0f9803cc0a3dc881
>>> Commit message: Ignore memb_join messages during flush operations
>>> I had a look at this commit, and it seems to me it's dropping too 
>>> many packets:
>>> Because of this commit, while totemrrp_recv_flush() is called, 
>>> Corosync drops memb_join packets, but also ORF tokens. In the end, 
>>> it seems that sometimes, we drop so many of them that Corosync marks 
>>> the ring as faulty.
>>> To fix that, I've made the patch joined to this mail 
>>> (corosync-fix-token-drop.patch).
>>> However I wonder why this packet dropping is done at such a low 
>>> layer. Wouldn't it be more appropriate to do it in totemsrp.c ?
>>> Moreover, it seems to me that totemrrp_recv_flush() is called every 
>>> times Corosync get an ORF token (in message_handler_orf_token()). It 
>>> seems weird to me because the commit message says the packets should 
>>> only be dropped when we are in gather state to avoid switching 
>>> suddenly to recovery state.
>>> Also, could you tell me if this packet dropping could explain the 2 
>>> other behaviors I observed ?
>>> Thanks in advance,
>>> Regards,
>>> _______________________________________________
>>> discuss mailing list
>>> discuss at corosync.org
>>> http://lists.corosync.org/mailman/listinfo/discuss

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