linux-kernel - Re: Mounting NFS root FS

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Message-Id: <1165256490.711.233.camel@lade.trondhjem.org>
Date:	Mon, 04 Dec 2006 13:21:30 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Janne Karhunen <Janne.Karhunen@...il.com>
Cc:	MrUmunhum@...dial.com, linux-kernel@...r.kernel.org
Subject: Re: Mounting NFS root FS

On Mon, 2006-12-04 at 19:12 +0200, Janne Karhunen wrote:
> > 2) NFS provides persistent storage.
> 
> To me this sounds like a chicken and an egg problem. It 
> both depends and provides this at the same time :/. But 
> hey, if it's supposed to work then OK.

??? Locking depends on persistent storage, but persistent storage never
depended on locking. Neither rpc.statd nor lockd, nor the nfs client
depend on locking working a priori.

> Anyhoo, I tried this at some stage and failed as random
> clients seemed to occasionally get stuck in insmod¹ at
> boot (infinite wait on lock that never gets released). 
> At that stage guess was that server could not properly 
> recognize client reboot given stale client lock data.
> But if it's supposed to work I guess I have to give it 
> another shot and do better analysis on it.
> 
> What about NLM/NSM protocol issues - do they properly 
> deal with packet loss and clients that stay down (client 
> holding a lock crashing and staying down; will the lock 
> ever be released)?

1) Packet loss is dealt with by retrying ad-infinitum.

2) No. The problem of client crashes was fixed in NFSv4 with the
addition of lease-based locks.

> ¹ And why does insmod require a lock on module at load??

Does it? I've no idea why it should need that.

Trond

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