Message-ID: <4EF71125.1060901@tonian.com>
Date: Sun, 25 Dec 2011 14:03:49 +0200
From: Benny Halevy <bhalevy@tonian.com>
MIME-Version: 1.0
To: Trond Myklebust <Trond.Myklebust@netapp.com>
CC: tigran.mkrtchyan@desy.de, linux-nfs <linux-nfs@vger.kernel.org>
Subject: Re: Session timeout on RHEL6.2
References: <CAGue13pWcOKeQH9nr=VK2ZCMLpC2s1=yQwuyxAEuuizjSh1Z+g@mail.gmail.com>  <1324475851.7709.12.camel@lade.trondhjem.org>  <CAGue13pSKnxNK_UWnh0KXz_w-CbeWQjmDS1H7ZBVMRiV25JqmQ@mail.gmail.com>  <4EF6A898.2010207@tonian.com> <1324806463.2740.6.camel@lade.trondhjem.org>
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On 2011-12-25 11:47, Trond Myklebust wrote:
> On Sun, 2011-12-25 at 06:37 +0200, Benny Halevy wrote: 
>> On 2011-12-21 22:11, Tigran Mkrtchyan wrote:
>>> On Wed, Dec 21, 2011 at 2:57 PM, Trond Myklebust
>>> <Trond.Myklebust@netapp.com> wrote:
>>>> On Wed, 2011-12-21 at 10:24 +0100, Tigran Mkrtchyan wrote:
>>>>> Dear friends,
>>>>>
>>>>> We are observing strange behavior with RHEL 6.2:
>>>>>
>>>>> Our the server lease time is 90 seconds. I can see that client
>>>>> sends SEQUENCE every 60 sec. And this is for some hours ( ~8 ).
>>>>> At some point client sends SEQUENCE after 127 seconds and
>>>>> gets, as expected, EXPIRED.
>>>>
>>>> Why shouldn't the client be allowed to let the lease expire if nothing
>>>> is using that filesystem?
>>>>
>>>>> I this point I have to blame myself.
>>>>> Client comes with EXCHANGE_ID using the same clientid.
>>>>> We did not garbage collected clientid internally as this happens after
>>>>> 2*LEASE_TIME
>>>>> and return EXPIRE. This ping-pong never ends.
>>>>>
>>>>> This is probably mostly a bug on my side. Nevertheless we never observed late
>>>>> SEQUENCE with kernel > 2.6.39. A short packet dump attached.
>>>>>
>>>>> I can open bug at RHEL if required.
>>>>
>>>> I wouldn't consider that a bug.
>>>
>>> As I said, there is a bug in exchange_id processing ( case 3 ) on my
>>> side. But to me it's sounds strange that client after more than 8
>>> hours of sending only sequence decided to send one of them later than
>>> lease time. Especially, that we did not have it with other kernels.
>>
>> I'm inclined to agree.  The client can let the lease expire for sure
>> and that's not a bug but the fact that the client sent the SEQUENCE operation
>> after the lease had expired indicates it might not be aware of that fact
>> and that seems to be a client bug.
>>
>> That said, I don't think that letting the lease expire when the client is idle
>> is the most polite thing to do. Why let the server clean up after the client
>> and revert to possibly un-optimized recovery paths rather than orderly
>> destruction of the state by the client?
> 
> There are plenty of cases where the client can be idle for hours or even
> _days_. What's the point of pinging the server all the time after
> working hours?
> 
> If someone wants to code up a DESTROY_SESSION and DESTROY_CLIENTID in
> order to make it formal, then fine, however note that we don't even do
> that on a full unmount today.
> 

The heavy lifting is releasing locks and returning layouts and delegations
sending DESTROY_{SESSION,CLIENTID} would be nice to have but I don't think
it's the most important issue.

Benny