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Date:   Thu, 4 Mar 2021 09:42:28 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Timo Rothenpieler <timo@rothenpieler.org>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: NFSD Regression: client observing a file while other client
 writes to it leads to stale local cache
Message-ID: <20210304144228.GD17512@fieldses.org>
References: <c3efd7e8-dc08-ac1f-9bee-7a7b0d8ac5fb@rothenpieler.org>
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On Tue, Mar 02, 2021 at 02:23:05AM +0100, Timo Rothenpieler wrote:
> Server and reading client disagreeing about the files size and
> contents is 100% reproducible, even after the writing client has
> long and definitely closed the file.

OK, I reproduced this myself and watched the network traffic in
Wireshark.

The server is *not* giving out a read delegation to the writer (which is
what the commit you bisected to should have allowed).  It *is* giving
out a delegation to the reader.  Which is a truly awful bug.
Investigating....

--b.