Subject: Re: Deadlock in NFSv4 in all kernels
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: "William A. (Andy) Adamson" <androsadamson@gmail.com>
Cc: Lukas Hejtmanek <xhejtman@ics.muni.cz>, linux-nfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        salvet@ics.muni.cz
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References: <20100507153920.GP28167@ics.muni.cz>
	 <AANLkTimsQTYWndbQo2nU01pcJfTRSZlPCMEY8m-CnksM@mail.gmail.com>
	 <20100525140240.GG9731@ics.muni.cz>
	 <AANLkTimfHrXViu0Zm75i4cFED7pXqAvv2edmKRpIi4me@mail.gmail.com>
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Date: Tue, 25 May 2010 10:29:45 -0400
Message-ID: <1274797785.5377.50.camel@heimdal.trondhjem.org>
Sender: linux-nfs-owner@vger.kernel.org
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On Tue, 2010-05-25 at 10:10 -0400, William A. (Andy) Adamson wrote: 
> 2010/5/25 Lukas Hejtmanek <xhejtman@ics.muni.cz>:
> > On Tue, May 25, 2010 at 09:45:32AM -0400, William A. (Andy) Adamson wrote:
> >> Not get into the problem in the first place: this means
> >>
> >> 1) determine a 'lead time' where the NFS client declares a context
> >> expired even though it really as 'lead time' until it actually
> >> expires.
> >>
> >> 2) flush all writes on any contex that will expire within the lead
> >> time which needs to be long enough for flushes to take place.
> >
> > I think you cannot give any guarantees that the flush happens on time. There
> > can be server overload, network overload, anything and you are out of luck.
> 
> True - but this will be the case no matter what scheme is in place.
> The above is to handle the normal working situation. When this fails
> due to network, server overload, server reboot, i.e. not-normal
> situation, then use the machine credential.

Use of the machine credential also requires help from the rpc.gssd
daemon. It's not a solution to the deadlock Lukas is describing.

Trond