Session timeout on RHEL6.2

Session timeout on RHEL6.2

[Tigran Mkrtchyan]

[-- Attachment #1: Type: text/plain, Size: 699 bytes --]

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.

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.

Regards,
   Tigran.

[-- Attachment #2: sequence.dump --]
[-- Type: application/octet-stream, Size: 3112 bytes --]

Re: Session timeout on RHEL6.2

[Trond Myklebust]

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.

Trond
-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com

Re: Session timeout on RHEL6.2

[Tigran Mkrtchyan]

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.

Anyway, we will update our server tomorrow with bugfix.

Tigran.

>
> Trond
> --
> Trond Myklebust
> Linux NFS client maintainer
>
> NetApp
> Trond.Myklebust@netapp.com
> www.netapp.com
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Session timeout on RHEL6.2

[Benny Halevy]

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?

Benny

> 
> Anyway, we will update our server tomorrow with bugfix.
> 
> Tigran.
> 
>>
>> Trond
>> --
>> Trond Myklebust
>> Linux NFS client maintainer
>>
>> NetApp
>> Trond.Myklebust@netapp.com
>> www.netapp.com
>>

Re: Session timeout on RHEL6.2

[Trond Myklebust]

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.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com

Re: Session timeout on RHEL6.2

[Benny Halevy]

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

Re: Session timeout on RHEL6.2

[Trond Myklebust]

On Sun, 2011-12-25 at 14:03 +0200, Benny Halevy wrote: 
> 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.

Actually, that requirement to return state is what makes
DESTROY_CLIENTID a completely useless operation.
Forget what I said then: it's too stupid to implement...

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com

Re: Session timeout on RHEL6.2

[Tigran Mkrtchyan]

Hi Trond,

There is a small inconsistency in your theory: to close idle session
it's enough not to send sequence any more and there are no reason to
re-establish session as soon as server returns EXPIRED.

Tigran.

On Sun, Dec 25, 2011 at 2:25 PM, Trond Myklebust
<Trond.Myklebust@netapp.com> wrote:
> On Sun, 2011-12-25 at 14:03 +0200, Benny Halevy wrote:
>> 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.
>
> Actually, that requirement to return state is what makes
> DESTROY_CLIENTID a completely useless operation.
> Forget what I said then: it's too stupid to implement...
>
> --
> Trond Myklebust
> Linux NFS client maintainer
>
> NetApp
> Trond.Myklebust@netapp.com
> www.netapp.com
>

RE: Session timeout on RHEL6.2

[Myklebust, Trond]

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Re: Session timeout on RHEL6.2

[Tigran Mkrtchyan]

On Fri, Dec 30, 2011 at 2:03 AM, Myklebust, Trond
<Trond.Myklebust@netapp.com> wrote:
>> -----Original Message-----
>> From: Tigran Mkrtchyan [mailto:tigran.mkrtchyan@desy.de]
>> Sent: Thursday, December 29, 2011 8:21 PM
>> To: Myklebust, Trond
>> Cc: Benny Halevy; linux-nfs
>> Subject: Re: Session timeout on RHEL6.2
>>
>> Hi Trond,
>>
>> There is a small inconsistency in your theory: to close idle session it's enough
>> not to send sequence any more and there are no reason to re-establish
>> session as soon as server returns EXPIRED.
>
> I don't understand. I've never put forward any "theory" involving forcing the client to re-establish the session just because the server returns EXPIRED. It should be re-establishing sessions iff we want to access the filesystem and the server tells it that the session expired.

My apologies if I was not clear. I just wanted to say that it doesn't
looks like expected client behavior.

Tigran.

>
> Trond
>
>
>> Tigran.
>>
>> On Sun, Dec 25, 2011 at 2:25 PM, Trond Myklebust
>> <Trond.Myklebust@netapp.com> wrote:
>> > On Sun, 2011-12-25 at 14:03 +0200, Benny Halevy wrote:
>> >> 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.
>> >
>> > Actually, that requirement to return state is what makes
>> > DESTROY_CLIENTID a completely useless operation.
>> > Forget what I said then: it's too stupid to implement...
>> >
>> > --
>> > Trond Myklebust
>> > Linux NFS client maintainer
>> >
>> > NetApp
>> > Trond.Myklebust@netapp.com
>> > www.netapp.com
>> >