lockd grace period

lockd grace period

[mehta kiran]

Hi , 
        lockd is used by both nfs and autofs
if there are 2 machines runnnig 2.6 kernel
(Red Hat) .autofs and nfs both are running
on system1.When nfs is failed over to system2
, all daemons start on system2 , but
lockd on system1 is still alive as it is required
by autofs "client"(this machine has automounted
filesystem from some other machine).After say 5
minutes , if nfs
is failed over to system1 , lockd recovery
gives some problem.statd notifies client , 
but when client tries to reclaim lock , 
LOCK routine returns "unknown error"(30000).
Is is because  , lockd was runnnig since long
time on system1 and hence its grace period was over.

But I dont face same problem of sles9 sp1.
What is the expected behaviour.?
Is it that whenever nfsd starts  , lockd should enter
grace period ?
or
Is is that lockd should enter grace period only when
it restarts without caring for nfs.?

--thanks,
   kiran



	
		
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Re: lockd grace period

[Steve Dickson]

mehta kiran wrote:

>What is the expected behaviour.?
>Is it that whenever nfsd starts  , lockd should enter
>grace period ?
>or
>Is is that lockd should enter grace period only when
>it restarts without caring for nfs.?
>  
>
Yes and Yes... When a NFS server is restarted, there is a grace
period in which the server (i.e. lockd) will accept reclaimed locks.
And it appears that reclaimed locks will also be accepted after
the grace period expires so its not clear who and how that
error is being generated....

steved.


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RE: lockd grace period

[Aswathanarayana, Chetan (STSD)]

Steved wrote :

> Yes and Yes... When a NFS server is restarted, there is a grace period
in which the server (i.e. lockd) will accept reclaimed locks.
> And it appears that reclaimed locks will also be accepted after the
grace period expires=20

I think reclaim locks should not be accepted after the grace period
expires, because it can cause data corruption.

Say, a reclaim request arrives after grace period and get's lock. There
will be time frame between end of grace period and arrival of
Reclaim request, in which case any thing can happen(ex: a new request
could be granted, it may make some changes to a file and unlock by the
time Reclaim arrives).

In which case reclaim thinks that it was the same original file it had
last locked.

So reclaim after grace period is not a good idea.

Mehta's question :

>What is the expected behaviour.?
>Is it that whenever nfsd starts  , lockd should enter grace period ?
>or
>Is is that lockd should enter grace period only when it restarts=20
>without caring for nfs.?

The lockd should enter grace period whenever nfsd starts/restarts.

~Chetan


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RE: lockd grace period

[mehta kiran]

Hi , 
          this means that if  lockd alone is running
since a long time and if now i start nfsd , lockd will
enter grace period and hence reclaim request
will only be served for grace period interval

In example given by chetan :
      I think  if reclaim request arrive after grace
period,it will be considered as normal lock request , 
and if lock has already been acquired by some other
client (between grace period end  and request arrival)
, appropriate error will be returned to 
requestor.

--thanks , 
   kiran


--- "Aswathanarayana, Chetan (STSD)"
<chetan.aswathanarayana@hp.com> wrote:

> Steved wrote :
> 
> > Yes and Yes... When a NFS server is restarted,
> there is a grace period
> in which the server (i.e. lockd) will accept
> reclaimed locks.
> > And it appears that reclaimed locks will also be
> accepted after the
> grace period expires 
> 
> I think reclaim locks should not be accepted after
> the grace period
> expires, because it can cause data corruption.
> 
> Say, a reclaim request arrives after grace period
> and get's lock. There
> will be time frame between end of grace period and
> arrival of
> Reclaim request, in which case any thing can
> happen(ex: a new request
> could be granted, it may make some changes to a file
> and unlock by the
> time Reclaim arrives).
> 
> In which case reclaim thinks that it was the same
> original file it had
> last locked.
> 
> So reclaim after grace period is not a good idea.
> 
> Mehta's question :
> 
> >What is the expected behaviour.?
> >Is it that whenever nfsd starts  , lockd should
> enter grace period ?
> >or
> >Is is that lockd should enter grace period only
> when it restarts 
> >without caring for nfs.?
> 
> The lockd should enter grace period whenever nfsd
> starts/restarts.
> 
> ~Chetan
> 



		
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Re: lockd grace period

[Steve Dickson]

mehta kiran wrote:

>Hi , 
>          this means that if  lockd alone is running
>since a long time and if now i start nfsd , 
>
hmm... why would you ever have lockd running "alone"?
Meaning what good is it w/out rpc.nfsd? Also how are
you doing that since one of the first things rpc.nfsd does
is bring up lockd().....

steved.



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Re: lockd grace period

[mehta kiran]

Hi , 
     lockd can run alone if this machine also acts
as nfs client of some other (third machine)
Clients side only require lockd and rpciod , right 
thanks,
kiran
--- Steve Dickson <SteveD@redhat.com> wrote:

> 
> 
> mehta kiran wrote:
> 
> >Hi , 
> >          this means that if  lockd alone is
> running
> >since a long time and if now i start nfsd , 
> >
> hmm... why would you ever have lockd running
> "alone"?
> Meaning what good is it w/out rpc.nfsd? Also how are
> you doing that since one of the first things
> rpc.nfsd does
> is bring up lockd().....
> 
> steved.
> 
> 
> 
>
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Re: lockd grace period

[Steve Dickson]

mehta kiran wrote:

>Hi , 
>     lockd can run alone if this machine also acts
>as nfs client of some other (third machine)
>Clients side only require lockd and rpciod , right 
>  
>
hmm... I always think of lockd being a server only process...
but indeed it is started for callbacks and reclaims on the client side so
so point taken... I guess what threw me was the idea of lockd
running "alone".... lockd never runs along (i.e. w/out
some type of NFS activity)....

So your question is, when there is already an active NFS mount
(which would bring up lockd()) and then NFS server is started
will lockd() have a grace period. From what I see the answer
is no. Probably because the its expected that the server will
be started before any NFS would occur which does occur
99% of the time....

steved.



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Re: lockd grace period

[Steve Dickson]

Aswathanarayana, Chetan (STSD) wrote:

>Say, a reclaim request arrives after grace period and get's lock. There
>will be time frame between end of grace period and arrival of
>Reclaim request, in which case any thing can happen(ex: a new request
>could be granted, it may make some changes to a file and unlock by the
>time Reclaim arrives).
>  
>
Nobody  is saying this NLM protocol or method of recovery is perfect.... 
;-)  This
is one of many reasons why the locking protocol is not integrated with the
NFSv4 protocol...

steved.



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Re: lockd grace period

[mehta kiran]

Hi , 
         but can u please let me know whether
 lockd which has been running before nfsd started
will enter grace period  or not
and will only server reclaim request ot not
thanks ,
 kiran
--- Steve Dickson <SteveD@redhat.com> wrote:

> Aswathanarayana, Chetan (STSD) wrote:
> 
> >Say, a reclaim request arrives after grace period
> and get's lock. There
> >will be time frame between end of grace period and
> arrival of
> >Reclaim request, in which case any thing can
> happen(ex: a new request
> >could be granted, it may make some changes to a
> file and unlock by the
> >time Reclaim arrives).
> >  
> >
> Nobody  is saying this NLM protocol or method of
> recovery is perfect.... 
> ;-)  This
> is one of many reasons why the locking protocol is
> not integrated with the
> NFSv4 protocol...
> 
> steved.
> 
> 



		
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Re: lockd grace period

[Dan Stromberg]

[-- Attachment #1: Type: text/plain, Size: 741 bytes --]

On Mon, 2005-01-31 at 09:58 -0500, Steve Dickson wrote:
> Aswathanarayana, Chetan (STSD) wrote:
> 
> >Say, a reclaim request arrives after grace period and get's lock. There
> >will be time frame between end of grace period and arrival of
> >Reclaim request, in which case any thing can happen(ex: a new request
> >could be granted, it may make some changes to a file and unlock by the
> >time Reclaim arrives).
> >  
> >
> Nobody  is saying this NLM protocol or method of recovery is perfect.... 
> ;-)  This
> is one of many reasons why the locking protocol is not integrated with the
> NFSv4 protocol...
> 
> steved.

I thought finally integrating locking into the protocol was supposed to
be a "feature" of NFSv4?



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Re: lockd grace period

[Trond Myklebust]

m=E5 den 31.01.2005 Klokka 15:07 (-0800) skreiv Dan Stromberg:

> I thought finally integrating locking into the protocol was supposed to
> be a "feature" of NFSv4?

Yes, it is, but note that the way NFSv4 does locking is VERY different
from NLM (particularly so in the way it handles client and server
reboot) due to the fact that it is based on the concept of leases.

I assume that is what Steve meant to say.

Cheers,
  Trond

--=20
Trond Myklebust <trond.myklebust@fys.uio.no>



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Re: lockd grace period

[Steve Dickson]

Dan Stromberg wrote:

>On Mon, 2005-01-31 at 09:58 -0500, Steve Dickson wrote:
>  
>
>>Aswathanarayana, Chetan (STSD) wrote:
>>
>>    
>>
>>>Say, a reclaim request arrives after grace period and get's lock. There
>>>will be time frame between end of grace period and arrival of
>>>Reclaim request, in which case any thing can happen(ex: a new request
>>>could be granted, it may make some changes to a file and unlock by the
>>>time Reclaim arrives).
>>> 
>>>
>>>      
>>>
>>Nobody  is saying this NLM protocol or method of recovery is perfect.... 
>>;-)  This
>>is one of many reasons why the locking protocol is not integrated with the
>>NFSv4 protocol...
>>
>>steved.
>>    
>>
>
>I thought finally integrating locking into the protocol was supposed to
>be a "feature" of NFSv4?
>  
>
My bad... s/is not/is/

steved.


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Re: lockd grace period

[mehta kiran]

Hi  , 
        I verified that suse NFS server enters
grace period whenever nfsd starts , irrespective
of whether lockd was already runnnig or not.
While Red Hat NFS server (RHEL 4 pre_rc2) does
not restart grace period of already running
lockd , even if nfsd restarts.

**Can anybody let me know what the standard behaviour
  should be. ??

What i think is that suse does it right by restarting
nfs grace period of already running lockd.
This is because machine acting as nfs server
can definitely act as nfs client of some other
machine(though rare but occurs).

Will nfs developers from Suse "also" like to comment
on this?

thanks,
-- kiran

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