Date: Wed, 4 Jun 1997 16:57:19 +0100 (BST) From: Doug Rabson <dfr@nlsystems.com> To: John Polstra <jdp@polstra.com> Cc: freebsd-bugs@hub.freebsd.org Subject: Re: kern/3771 NFS hangs when writing to local FS re-mounted via NFS Message-ID: <Pine.BSF.3.95q.970604165410.394F-100000@herring.nlsystems.com> In-Reply-To: <199706041546.IAA09459@austin.polstra.com>
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On Wed, 4 Jun 1997, John Polstra wrote: > > There is a deadly embrace style deadlock when you loopback mount > > a filesystem using NFSv3. I don't plan to try and fix this since > > I don't think loopback mounts are useful other than for trivial > > testing. > > What is it about the loopback interface that's different? This > affects CVSup to localhost too (with a deadlock), and that is > sometimes useful. I can't see how it could happen unless the > loopback interface is failing to behave like a stream transport > is supposed to behave. The deadly embrace is in NFS. The sequence of events is something like this: NFS client allocates a buffer and fills it with data NFS client does a write rpc and locks the socket to read the reply NFS server gets the write rpc and starts to process it NFS server allocates a buffer to write the data VFS runs out of clean buffers and picks a dirty one (B_NEEDCOMMIT|B_DELWRI) VFS calls NFS client to clean the buffer NFS client tries to do a commit rpc but hangs because the socket is locked -- Doug Rabson Mail: dfr@nlsystems.com Nonlinear Systems Ltd. Phone: +44 181 951 1891 Fax: +44 181 381 1039
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