[Bug 1833758] Re: lvm2: vgcfgbackup in postinst takes several minutes

[Brian Murray]

I tested this on an virtual machine running Eoan and did not notice
vgcfgbackup taking as much time as it doesn in an schroot.

bdmurray at clean-eoan-amd64:~$ sudo time vgcfgbackup
0.00user 0.00system 0:00.02elapsed 37%CPU (0avgtext+0avgdata 10848maxresident)k
3584inputs+0outputs (0major+1411minor)pagefaults 0swaps

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Title:
  lvm2: vgcfgbackup in postinst takes several minutes

Status in lvm2 package in Ubuntu:
  New

Bug description:
  The postinst for lvm2 includes a call to vgcfgbackup; in the version
  included in eoan 2.03.02-2ubuntu4 (and 2.03.02-2ubuntu3 before it),
  this command takes several minutes to run when invoked in an schroot
  as happens when a building a package with sbuild that ends up pulling
  lvm2 as part of its build dependency chain. An example package with
  lvm2 in its build depends is rsnapshot, but this behavior was seen
  with a build of glibc. Some notes:

    - this behavior is NOT seen with the version of lvm2 in disco.
    - this happens in bionic with a 4.15 kernel and disco with a 5.0 kernel (different hosts, so different sets of block devices)
    - this happens regardless of whether the host is currently using logical volumes or not

  Here's the time difference between running the disco version and the
  eoan version:

  (disco-amd64)root at HOSTNAME:~# time vgcfgbackup
    WARNING: Failed to connect to lvmetad. Falling back to device scanning.

  real    0m0.204s
  user    0m0.014s
  sys     0m0.010s

  (eoan-amd64)root at HOSTNAME:~# time vgcfgbackup
    WARNING: Device /dev/sda not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda2 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda3 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb2 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb3 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdc not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdc1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdd not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdd1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sde not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sde1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sde2 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda2 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sda3 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb2 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdb3 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdc1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sdd1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sde1 not initialized in udev database even after waiting 10000000 microseconds.
    WARNING: Device /dev/sde2 not initialized in udev database even after waiting 10000000 microseconds.

  real    4m11.405s
  user    0m0.470s
  sys     0m0.576s

  /proc/mounts in the schroot:

  (eoan-amd64)root at HOSTNAME:~# cat /proc/mounts
  eoan-amd64 / overlay rw,relatime,lowerdir=/var/lib/schroot/union/underlay/eoan-amd64-29c7f791-9409-4505-9192-7c4685b8be34,upperdir=/srv/devel/schroot-overlays/eoan-amd64-29c7f791-9409-4505-9192-7c4685b8be34/upper,workdir=/srv/devel/schroot-overlays/eoan-amd64-29c7f791-9409-4505-9192-7c4685b8be34/work 0 0
  proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
  sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
  udev /dev devtmpfs rw,nosuid,relatime,size=10197712k,nr_inodes=2549428,mode=755 0 0
  devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
  /dev/sda2 /home ext4 rw,relatime,errors=remount-ro,data=ordered 0 0
  /dev/sda2 /tmp ext4 rw,relatime,errors=remount-ro,data=ordered 0 0
  tmpfs /run/shm tmpfs rw,relatime 0 0
  /dev/sda2 /scratch ext4 rw,relatime,errors=remount-ro,data=ordered 0 0
  /dev/sdc1 /srv/work ext4 rw,relatime,errors=remount-ro,data=ordered 0 0

  strace of vgcfgbackup is attached

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