Date: Fri, 16 Oct 1998 12:09:46 -0700 (PDT) From: jegelhof@cloud9.net To: freebsd-gnats-submit@FreeBSD.ORG Subject: kern/8345: mmap(2) hangs when dealing with certain files on NFS Message-ID: <199810161909.MAA17713@hub.freebsd.org>
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>Number: 8345 >Category: kern >Synopsis: mmap(2) hangs when dealing with certain files on NFS >Confidential: no >Severity: critical >Priority: high >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Fri Oct 16 12:10:00 PDT 1998 >Last-Modified: >Originator: James Egelhof >Organization: Cloud 9 Consulting, Inc. >Release: FreeBSD 2.2.7-STABLE >Environment: FreeBSD earl-grey.cloud9.net 2.2.7-STABLE FreeBSD 2.2.7-STABLE #0: Sat Sep 5 20:17:50 EDT 1998 jegelhof@earl-grey.cloud9.net:/usr/src/sys/compile/EARL-GREY i386 FreeBSD russian-caravan.cloud9.net 2.2.7-STABLE FreeBSD 2.2.7-STABLE #0: Mon Oct 12 18:18:49 EDT 1998 root@earl-grey.cloud9.net:/usr/src/sys/compile/RUSSIAN-CARAVAN i386 >Description: Programs that use mmap(2) can hang in the "vmopar" state. Programs stuck in that state cannot be killed or revived except by rebooting. This problem happens when the file being read via mmap is mounted over from another machine via NFS, and the file is appended to on the far machine. mmap fails regardless of the size of the file or of the append. >How-To-Repeat: Let's say that the NFS server is "Machine 1" and the client is "Machine 2." Mount a filesystem from Machine 1 onto Machine 2. Let's say the mount point is /mnt. Create a file of nontrivial length in /mnt; say, /mnt/test. Next we need to use a mmap-based utility that will run for a while. Good examples are sz (from the ports collection), cp (if the file is <8MB), and tail. sz is especially good because it will run for a while. machine1> sz /mnt/test [download begins] machine2> echo foo >> /the/filesystem/test [download dies] This will be the output from ps uxl: jegelhof 5539 0.0 0.2 228 536 p9- D 2:43PM 0:00.05 sz test2 (lsz) 349 5539 1 0 -18 0 228 536 vmopar D p9- 0:00.05 sz test2 (lsz) This problem does not occur if you disable the mmap code in the relevant appplication. We have tested this on a variety of hardware and with several different network configurations. This has been done with 10MB Ethernet, 10MB switched Ethernet, and 100MB switched Ethernet. We currently use Intel EtherExpress Pro 10/100B network cards and a Cisco Catalyst 2900XL 100MB switch. >Fix: Workaround is to disable mmap on every utility you use on NFS files. That is not a very good workaround because many FreeBSD standard utilities depend on mmap. Otherwise, mmap needs to be able to handle file size changes on NFS filesystems. >Audit-Trail: >Unformatted: To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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