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[Launchpad Bug Tracker <1714505@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package debian-installer-utils - 1.113ubuntu2

---------------
debian-installer-utils (1.113ubuntu2) artful; urgency=medium

  * Make sure udevd internal state is up-to-date before calling trigger &
    settle. This insures that newly anna-installed udev rules and kernel
    modules are loaded by udevd for correct processing of the udev
    rules. LP: #1714505.

 -- Dimitri John Ledkov <xnox@xxxxxxxxxx>  Sun, 17 Sep 2017 00:41:44
+0100

** Changed in: debian-installer-utils (Ubuntu)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1714505

Title:
  systemd kmod builtin uses out of date kmod context

Status in systemd:
  Fix Released
Status in debian-installer package in Ubuntu:
  New
Status in debian-installer-utils package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Won't Fix
Status in debian-installer source package in Trusty:
  New
Status in debian-installer source package in Xenial:
  New
Status in debian-installer source package in Zesty:
  New
Status in debian-installer source package in Artful:
  New

Bug description:
  [Impact]

  udev's rules use a built-in 'kmod' instead of the system
  modprobe/insmod, and this built-in kmod only validates/refreshes its
  kmod 'context' every 3 seconds (or longer) during event processing.

  However, because other parts of the system rely on udev to load
  modules correctly, it is not acceptable for it to use an out of date
  module context.  For example, during a system installation:

  -the system boots with kernel and initrd with a reduced set of modules, not including nvme module
  -udevd starts, and creates its kmod module context, which does not include nvme module
  -system installer adds 'block-modules' udeb, which adds nvme module to system
  -system installer immediately calls hw-detect->update-dev->udevadm trigger
  -udevd sees its kmod module context is not more than 3 seconds old, and does not update it
  -udevd rule 80-drivers.rules finds NVMe pci modalias and asks kmod builtin to load matching driver
  -udevd kmod builtin does not find NVMe pci modalias because its context is out of date

  this results in the system installer complaining to the user that it
  found no disks, even though there is a NVMe drive in the system, and
  the nvme module is installed in the system.

  [Test Case]

  This is reproducable when trying to install using debian-installer and
  a preseed file that skips all questions, although not on all systems,
  since other events can cause udevd to reload all its builtins, or the
  installer may take longer than 3 seconds to call udevadm trigger after
  installing the nvme module udeb.

  However, the bug is easily reproducable on any system with a nvme
  drive using this script:

  #!/bin/bash
  MOD_DIR=/lib/modules/$( uname -r )/kernel/drivers/nvme/host
  modprobe -rq nvme
  mv $MOD_DIR/nvme.ko .
  depmod -a
  sleep 3
  udevadm trigger
  sleep 1
  mv nvme.ko $MOD_DIR/
  depmod -a
  udevadm trigger
  sleep 3
  grep -q nvme /proc/partitions && echo PASS || echo FAIL

  that script does:
  1) remove nvme module from the system, reproducing situation where nvme module had not yet been installed
  2) waits 3 seconds, because the udev kmod validation timeout is 3 seconds
  3) triggers udev, which forces it to reload its kmod context (this could be done with udevadm control -R instead)
  4) waits 1 second for the udev trigger to finish, then puts the nvme module back into the system, reproducing the initial installation of the deb/udeb containing the nvme module
  5) immediately triggers udev, which should load the nvme module when it sees the nvme pci device
  6) wait 3 seconds for udev trigger to finish (plenty of time), and check if the nvme module was loaded

  this script reproduces the error every time, due to the stale kmod
  context.  With a fixed udev, this should succeed in loading the nvme
  module.

  [Regression Potential]

  The most potential for regression with a fix to this involves slowing
  down udev due to validating the kmod context for every kmod load call.
  However, slightly higher performance does not make up for broken
  operation.

  [Other Info]

  This needs fixing upstream, which I'm in progress on.

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