From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: RPC retransmission of write requests containing bogus data
Date: Fri, 17 Oct 2008 14:33:50 +0100
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Cc: linux-nfs@vger.kernel.org, mchan-dY08KVG/lbpWk0Htik3J/w@public.gmane.org
To: Trond Myklebust <Trond.Myklebust@netapp.com>
In-Reply-To: <1224249772.7722.9.camel@localhost>
Sender: linux-nfs-owner@vger.kernel.org

On Fri, 2008-10-17 at 09:22 -0400, Trond Myklebust wrote:
> On Fri, 2008-10-17 at 14:01 +0100, Ian Campbell wrote:
> > On Fri, 2008-10-17 at 08:48 -0400, Trond Myklebust wrote:
> > > I don't see how this could be an RPC bug. The networking layer is
> > > supposed to either copy the data sent to the socket, or take a reference
> > > to any pages that are pushed via the ->sendpage() abi.
> > > 
> > > IOW: the pages are supposed to be still referenced by the networking
> > > layer even if the NFS layer and page cache have dropped their
> > > references.
> > 
> > The pages are still referenced by the networking layer. The problem is
> > that the userspace app has been told that the write has completed so it
> > is free to write new data to those pages.
> > 
> > Ian.
> 
> OK, I see your point.
> 
> Does this happen at all with NFSv4? I ask because the NFSv4 client will
> always ensure that the TCP connection gets broken before a
> retransmission. I wouldn't therefore expect any races between a reply to
> the previous transmission and the new one...

I believe we've only tested with NFSv3.

Unfortunately I've just lent the box which reproduces this issue to a
colleague for the rest of the day. I'll test with v4 next week.

Ian.