So I'm reporting my current further findings here in case somebody else than me stumbles upon this bug report in search of help.
I'll not create a new bug report as of now, since I'm still researching the problem and I think there's no point in opening a new bug report if it'll turn out to be invalid anyway. So to the point: in my case the problem has been: 8 05:02:51 foo kernel: [987432.148305] device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception. after that umount goes berzerk: Nov 8 05:02:51 foo kernel: [987432.163602] Buffer I/O error on device dm-11, logical block 11985789 Nov 8 05:02:51 foo kernel: [987432.163638] Buffer I/O error on device dm-11, logical block 11985790 ... Nov 8 05:02:51 foo kernel: [987432.299393] EXT4-fs warning (device loop0): __ext4_read_dirblock:901: error reading directory block (ino 3539872, block 0) Nov 8 05:02:57 foo kernel: [987437.577541] quiet_error: 4396 callbacks suppressed Nov 8 05:02:57 foo kernel: [987437.577547] Buffer I/O error on device dm-11, logical block 12622895 Nov 8 05:02:57 foo kernel: [987437.577609] lost page write due to I/O error on dm-11 and now umount is hanging there with 100% CPU usage with no possibility to `kill` it. So one problem here is that the `lvsnapshot` is running out of `exception` space. Thus I should either allow the snapshot to be autoextended or to increase the `-L`size I have given it. But even so, umount shouldn't get stuck on the ext4 FS. Since I was `umount`ing without `-f` I will try that today and see what happens and report back here hopefully. -- 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/1115753 Title: Umount of Multiple LVM Snapshots Causes 'soft lockup CPU#0 stuck for' Status in linux package in Ubuntu: Invalid Bug description: Simultaneous umount of multiple lvm snapshots causes system to hang / freeze / deadlock. Window manager freezes. If umount is executed in a non window-manager tty, messages containing "BUG", "blocked for more than xx seconds", and a list of tasks associated with each of the 8 cpu cores will scroll up at regular intervals. The tasks assigned to each cpu core are unchanging over time, appearing to be deadlocked. No relevant information is left in system logs. Hard reset / poweroff is required. Problem does not occur 100% of the time. It is less likely to occur if umount is done shortly after mount. Problem still occurs -- but less frequently -- if lazy umount -l is used. Snapshots are read-only, and are mounted read-only. ProblemType: Bug DistroRelease: Ubuntu 12.04 Package: linux-image-3.2.0-37-generic 3.2.0-37.58 ProcVersionSignature: Ubuntu 3.2.0-37.58-generic 3.2.35 Uname: Linux 3.2.0-37-generic x86_64 AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24. ApportVersion: 2.0.1-0ubuntu17.1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC1: craig 3257 F.... pulseaudio /dev/snd/controlC0: craig 3257 F.... pulseaudio CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found. Card0.Amixer.info: Card hw:0 'SB'/'HDA ATI SB at 0xfeb00000 irq 16' Mixer name : 'Realtek ALC889' Components : 'HDA:10ec0889,1043846b,00100004' Controls : 49 Simple ctrls : 24 Card1.Amixer.info: Card hw:1 'HDMI'/'HDA ATI HDMI at 0xfea30000 irq 98' Mixer name : 'ATI R6xx HDMI' Components : 'HDA:1002aa01,00aa0100,00100100' Controls : 6 Simple ctrls : 1 Card1.Amixer.values: Simple mixer control 'IEC958',0 Capabilities: pswitch pswitch-joined penum Playback channels: Mono Mono: Playback [on] Date: Mon Feb 4 18:58:37 2013 HibernationDevice: RESUME=UUID=b788f786-ba76-4eb0-991f-d3bbc339d3f7 InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111011) IwConfig: lo no wireless extensions. eth0 no wireless extensions. MachineType: To be filled by O.E.M. To be filled by O.E.M. MarkForUpload: True ProcEnviron: TERM=xterm PATH=(custom, no user) LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: 0 VESA VGA ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.2.0-37-generic root=/dev/mapper/volgroup0-root ro RelatedPackageVersions: linux-restricted-modules-3.2.0-37-generic N/A linux-backports-modules-3.2.0-37-generic N/A linux-firmware 1.79.1 RfKill: SourcePackage: linux UpgradeStatus: Upgraded to precise on 2012-10-23 (104 days ago) dmi.bios.date: 09/27/2011 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 0813 dmi.board.asset.tag: To be filled by O.E.M. dmi.board.name: Crosshair V Formula dmi.board.vendor: ASUSTeK Computer INC. dmi.board.version: Rev 1.xx dmi.chassis.asset.tag: To Be Filled By O.E.M. dmi.chassis.type: 3 dmi.chassis.vendor: To Be Filled By O.E.M. dmi.chassis.version: To Be Filled By O.E.M. dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0813:bd09/27/2011:svnTobefilledbyO.E.M.:pnTobefilledbyO.E.M.:pvrTobefilledbyO.E.M.:rvnASUSTeKComputerINC.:rnCrosshairVFormula:rvrRev1.xx:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.: dmi.product.name: To be filled by O.E.M. dmi.product.version: To be filled by O.E.M. dmi.sys.vendor: To be filled by O.E.M. 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