[Bug 1834875] Re: cloud-init growpart race with udev

[Michael Hudson-Doyle]

Ah, no I think this might be along right lines: udev is calling blkid on
the _partition_ of course, so it can probe for filesystem etc without
looking at the partition table. After it's done that, it does look for
the partition table so it can read the ID_PART_ENTRY_* values from it,
but if it fails to load the partition table it just gives up and still
returns success.

As to how this might happen, well there are certainly moments during
sgdisk's writing of the partition table when the gpt data is not
completely consistent (it contains checksums and is not written
atomically). Two things are still a bit unsatisfactory about this
explanation though: 1) it's a mighty tight race, hitting this with any
regularity borders on the incredible and 2) I have no idea why this only
occurs on Azure on Cosmic up. Although I guess 1) may explain 2) I
suppose.

Setting LIBBLKID_DEBUG=lowprobe in systemd-udevd's environment during a
failing boot would be very interesting to confirm or deny this line of
reasoning -- although this will make udevd produce gobs of output and
possibly disturb any race.

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to systemd in Ubuntu.
https://bugs.launchpad.net/bugs/1834875

Title:
  cloud-init growpart race with udev

Status in cloud-init:
  Incomplete
Status in cloud-utils:
  New
Status in linux-azure package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  On Azure, it happens regularly (20-30%), that cloud-init's growpart
  module fails to extend the partition to full size.

  Such as in this example:

  ========================================

  2019-06-28 12:24:18,666 - util.py[DEBUG]: Running command ['growpart', '--dry-run', '/dev/sda', '1'] with allowed return codes [0] (shell=False, capture=True)
  2019-06-28 12:24:19,157 - util.py[DEBUG]: Running command ['growpart', '/dev/sda', '1'] with allowed return codes [0] (shell=False, capture=True)
  2019-06-28 12:24:19,726 - util.py[DEBUG]: resize_devices took 1.075 seconds
  2019-06-28 12:24:19,726 - handlers.py[DEBUG]: finish: init-network/config-growpart: FAIL: running config-growpart with frequency always
  2019-06-28 12:24:19,727 - util.py[WARNING]: Running module growpart (<module 'cloudinit.config.cc_growpart' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py'>) failed
  2019-06-28 12:24:19,727 - util.py[DEBUG]: Running module growpart (<module 'cloudinit.config.cc_growpart' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py'>) failed
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/cloudinit/stages.py", line 812, in _run_modules
      freq=freq)
    File "/usr/lib/python3/dist-packages/cloudinit/cloud.py", line 54, in run
      return self._runners.run(name, functor, args, freq, clear_on_fail)
    File "/usr/lib/python3/dist-packages/cloudinit/helpers.py", line 187, in run
      results = functor(*args)
    File "/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py", line 351, in handle
      func=resize_devices, args=(resizer, devices))
    File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 2521, in log_time
      ret = func(*args, **kwargs)
    File "/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py", line 298, in resize_devices
      (old, new) = resizer.resize(disk, ptnum, blockdev)
    File "/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py", line 159, in resize
      return (before, get_size(partdev))
    File "/usr/lib/python3/dist-packages/cloudinit/config/cc_growpart.py", line 198, in get_size
      fd = os.open(filename, os.O_RDONLY)
  FileNotFoundError: [Errno 2] No such file or directory: '/dev/disk/by-partuuid/a5f2b49f-abd6-427f-bbc4-ba5559235cf3'

  ========================================

  @rcj suggested this is a race with udev. This seems to only happen on
  Cosmic and later.

To manage notifications about this bug go to:
https://bugs.launchpad.net/cloud-init/+bug/1834875/+subscriptions