I made one more observation, and it is fully reproducible. Frankly, it would appear that the bug may not be as impactful as originally though (if this is a bug, to begin with). Here it is:
On one of the Linux clients, Windows runs in Virtualbox. The NFS share is mounted within the Linux host, and the mount point is available in the virtual environment as a vboxdrv shared folder. Within Windows, the user uses a translation automation tool called "Trados". If -- and only if -- this program is running, the apparent runaway kworker uses 100% CPU. When Trados is closed, the CPU core returns to idle within ~20 to 30 seconds. This, finally, explains many observations I made before, which are mere coincidences. It also explains why a second NFS server that I brought online today does not exhibit the runaway behavior. Only the combination of all three: NFS, Virtualbox (Win 7 guest), and Trados, puts a heavy load on the rpc daemon. No other Windows program in the virtual box does that. Why and how? I used tcpdump to see if anything insane is going on, but it is not -- neither on the client's physical eth0 interface nor on the virtual vboxnet0 interface. I did not find anything suspicious. Also, I cannot explain why the old 10.04 NFS server didn't show this behavior. NFSv3 perhaps? And why does it affect the rpc daemon? In conclusion, I believe that I found the cause (albeit not the reason) for the runaway behavior. I also believe that the combination of software packages is very unusual, and this bug is not likely to affect many people. I propose to reduce the importance level of this bug to "low". Latsly, it makes me shudder to think about what Trados might do to the hard disks of people who use it locally, with natively installed Windows. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1322407 Title: NFS kernel server creates a kworker with 100% CPU usage, then hangs randomly Status in “linux” package in Ubuntu: Confirmed Bug description: This concerns the server edition of 14.04. I have set up a NFS server. Once I attach at least one client, one kworker process starts to use 100% CPU. The runaway kworker returns to idle when I reset the NFS server daemon with "service nfs-kernel-server stop" followed by "service nfs-kernel-server start". With the nfs kernel server stopped, the CPU remains idle. With the nfs kernel server running, as soon as one client requests a connection, the kworker process jumps to 100% CPU again. After some random time, the nfs kernel server no longer accepts requests from clients. Restarting the service allows clients to reconnect. The syslog shows no relevant information. This problem has never appeared on a very similar server setup with 12.04. Configration: The svcgssd is not running. I played with various configurations (enabling/disabling NFSv3 and NFSv4), but it makes no difference. I tried to enable event debugging: #> echo workqueue:workqueue_queue_work > /sys/kernel/debug/tracing/set_event #> cat /sys/kernel/debug/tracing/trace_pipe > /var/tmp/kerntrace.txt and found the following kernel trace in a tight loop: [...] kworker/2:1-86 [002] d... 161940.910668: workqueue_queue_work: work struct=ffff8804140675e0 function=xs_tcp_setup_socket [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d.s. 161940.910674: workqueue_queue_work: work struct=ffff8800cef9f488 function=rpc_async_schedule [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d... 161940.910675: workqueue_queue_work: work struct=ffff8804140675e0 function=xs_tcp_setup_socket [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d.s. 161940.910681: workqueue_queue_work: work struct=ffff8800cef9f488 function=rpc_async_schedule [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d... 161940.910682: workqueue_queue_work: work struct=ffff8804140675e0 function=xs_tcp_setup_socket [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d.s. 161940.910688: workqueue_queue_work: work struct=ffff8800cef9f488 function=rpc_async_schedule [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d... 161940.910689: workqueue_queue_work: work struct=ffff8804140675e0 function=xs_tcp_setup_socket [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d.s. 161940.910695: workqueue_queue_work: work struct=ffff8800cef9f488 function=rpc_async_schedule [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d... 161940.910696: workqueue_queue_work: work struct=ffff8804140675e0 function=xs_tcp_setup_socket [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 kworker/2:1-86 [002] d.s. 161940.910702: workqueue_queue_work: work struct=ffff8800cef9f488 function=rpc_async_schedule [sunrpc] workqueue=ffff8800cfbb6a00 req_cpu=256 cpu=2 [...] At present, I have to consider NFS fubar. Thanks, Mark ProblemType: Bug DistroRelease: Ubuntu 14.04 Package: linux-image-3.13.0-24-generic 3.13.0-24.47 ProcVersionSignature: Ubuntu 3.13.0-24.47-generic 3.13.9 Uname: Linux 3.13.0-24-generic x86_64 AlsaVersion: Advanced Linux Sound Architecture Driver Version k3.13.0-24-generic. AplayDevices: Error: [Errno 2] No such file or directory: 'aplay' ApportVersion: 2.14.1-0ubuntu3.1 Architecture: amd64 ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord' AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/controlC0', '/dev/snd/hwC0D0', '/dev/snd/pcmC0D0c', '/dev/snd/pcmC0D0p', '/dev/snd/pcmC0D1p', '/dev/snd/pcmC0D2c', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1: CRDA: Error: [Errno 2] No such file or directory: 'iw' Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer' Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer' Date: Thu May 22 22:48:48 2014 HibernationDevice: RESUME=UUID=adcdeef5-9b46-4ea4-b9f4-b6e642ea91e8 InstallationDate: Installed on 2014-05-12 (10 days ago) InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2) IwConfig: eth0 no wireless extensions. lo no wireless extensions. MachineType: Gigabyte Technology Co., Ltd. GA-990XA-UD3 ProcEnviron: TERM=xterm PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: 0 nouveaufb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-24-generic root=UUID=6cf411b3-3e8e-41e5-8670-db14ad259f58 ro IOMMU=soft nomdmonddf nomdmonisw RelatedPackageVersions: linux-restricted-modules-3.13.0-24-generic N/A linux-backports-modules-3.13.0-24-generic N/A linux-firmware 1.127.2 RfKill: Error: [Errno 2] No such file or directory: 'rfkill' SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) WifiSyslog: dmi.bios.date: 10/13/2011 dmi.bios.vendor: Award Software International, Inc. dmi.bios.version: F9 dmi.board.name: GA-990XA-UD3 dmi.board.vendor: Gigabyte Technology Co., Ltd. dmi.board.version: x.x dmi.chassis.type: 3 dmi.chassis.vendor: Gigabyte Technology Co., Ltd. dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF9:bd10/13/2011:svnGigabyteTechnologyCo.,Ltd.:pnGA-990XA-UD3:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-990XA-UD3:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr: dmi.product.name: GA-990XA-UD3 dmi.sys.vendor: Gigabyte Technology Co., Ltd. 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