Date:   Sun, 9 Jan 2022 17:41:24 -0500
From:   "'bfields@fieldses.org'" <bfields@fieldses.org>
To:     NeilBrown <neilb@suse.de>
Cc:     "inoguchi.yuki@fujitsu.com" <inoguchi.yuki@fujitsu.com>,
        'Trond Myklebust' <trondmy@hammerspace.com>,
        "'linux-nfs@vger.kernel.org'" <linux-nfs@vger.kernel.org>,
        "'mbenjami@redhat.com'" <mbenjami@redhat.com>
Subject: Re: client caching and locks
Message-ID: <20220109224124.GC1589@fieldses.org>
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 <20220103162041.GC21514@fieldses.org>
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On Mon, Jan 10, 2022 at 08:58:55AM +1100, NeilBrown wrote:
> On Thu, 06 Jan 2022, 'bfields@fieldses.org' wrote:
> 
> > +Locking can also provide cache consistency:
> >  .P
> > -NLM supports advisory file locks only.
> > -To lock NFS files, use
> > -.BR fcntl (2)
> > -with the F_GETLK and F_SETLK commands.
> > -The NFS client converts file locks obtained via
> > -.BR flock (2)
> > -to advisory locks.
> > +Before acquiring a file lock, the client revalidates its cached data for
> > +the file.  Before releasing a write lock, the client flushes to the
> > +server's stable storage any data in the locked range.
> 
> Surely the client revalidates *after* acquiring the lock on the server. 
> Otherwise the revalidation has now value.

Gah.

@@ -1489,9 +1493,9 @@ locks.
 .P
 Locking can also provide cache consistency:
 .P
-Before acquiring a file lock, the client revalidates its cached data for
-the file.  Before releasing a write lock, the client flushes to the
-server's stable storage any data in the locked range.
+After acquiring a file lock and before using any cached data, the client
+revalidates its cache.  Before releasing a write lock, the client flushes to
+the server's stable storage any data in the locked range.
 .P
 A distributed application running on multiple NFS clients can take a
 read lock for each range that it reads and a write lock for each range that

--b.