[Bug 1820001] Re: vgcfgbackup stuck in kernel, causing lvm and udevd block forever

[Aleksandr Kichigin]

** Attachment added: "journalctl"
   https://bugs.launchpad.net/ubuntu/+source/lvm2/+bug/1820001/+attachment/5245988/+files/journalctl-part.txt

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Title:
  vgcfgbackup stuck in kernel, causing lvm and udevd block forever

Status in lvm2 package in Ubuntu:
  New

Bug description:
  Hello

  I am using lvm snapshots over sofware raid with 4 devices for rsync
  backups.

  Recently I found out that it is stuck and any operaton with lvm is stuck as well.
  This also causes 1000+ processes of systemd-udevd to be in interpretable sleep and cannot be killed.

  
  My backup script looks like this:

  /sbin/vgcfgbackup -qq main
  /sbin/lvcreate -qq --size 20G --snapshot --name backup /dev/mapper/main-root
  mount /dev/mapper/main-backup /mnt/root_snapshot
  *rsync stuff*
  umount /mnt/root_snapshot
  /sbin/lvremove -yqq /dev/mapper/main-backup

  
  Launching as not root `pvs --unbuffered --readonly -t -vvvv` is stuck at:
  #filters/filter-persistent.c:51     Wiping cache of LVM-capable devices

  Launching as not root `lvs -vvvv --unbuffered --readonly -vvvv` us stuck at:
  #toollib.c:3736         Get list of VGs on system

  
  I have a lot of processes stucked (total number ~1000):

  root       756  0.0  0.0  56400  8428 ?        D    фев26   0:00 /sbin/vgcfgbackup -qq main
  root     21723  0.0  0.0  36940  1860 ?        D    мар13   0:00 /lib/systemd/systemd-udevd
  root     21724  0.0  0.0  36940  1808 ?        D    мар13   0:00 /lib/systemd/systemd-udevd
  root     21728  0.0  0.0  36940  1808 ?        D    мар13   0:00 /lib/systemd/systemd-udevd
  root     14541  0.0  0.0   7780  2524 ?        D    06:25   0:00 /sbin/mdadm --monitor --scan --oneshot
  root      8792  0.0  0.0  56548  8308 ?        D    05:59   0:00 lvs
  root     11343  0.0  0.0 119424  7632 ?        S    06:10   0:00 sudo lvs -vd
  admin    12112  0.0  0.0  56596  8368 ?        D    06:14   0:00 lvs -vvvv -dddddd --readonly -t --unbuffered

  
  In dmesg I have following logs:

  [16983388.190818] general protection fault: 0000 [#41] SMP PTI
  [16987988.464353] general protection fault: 0000 [#42] SMP PTI

  
  In system journal:

  Mar 14 06:47:35 - systemd[1]: systemd-udevd.service: Found left-over process 17886 (systemd-udevd) in control group while starting unit. Ignoring.
  Mar 14 06:47:35 - systemd[1]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.
  Mar 14 06:47:35- systemd[1]: systemd-udevd.service: Found left-over process 17887 (systemd-udevd) in control group while starting unit. Ignoring.
  Mar 14 06:50:28 - systemd-udevd[20282]: seq 1116768 '/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/sda1' is taking a long time
  Mar 14 06:50:28 - systemd-udevd[20282]: seq 1116780 '/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:1/1:0:1:0/block/sdc/sdc1' is taking a long time

  
  lvmdump hangs at `Gathering /dev listening`, but I was able to terminate it.

  
  mdstat:
  md0 : active raid10 sdb1[1] sdc1[2] sda1[0] sdd1[3]
        1953259520 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
        bitmap: 1/15 pages [4KB], 65536KB chunk

  
  OS: Ubuntu 18.04.1 LTS
  Kernel: 4.15.0-29-generic
  lvm2: 2.02.176-4.1ubuntu3

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