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[Dimitri John Ledkov <launchpad@xxxxxxxxxxxx>]

** Changed in: systemd (Ubuntu Artful)
       Status: New => Won't Fix

** Description changed:

  [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  correctly, it is not acceptable for it to use an out of date module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  -udevd kmod builtin does not find NVMe pci modalias because its context is out of date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.
  
+ The fix is to reload udevadm rules, as per upstream recommendation.
+ 
  [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.
+ Stale context in udevd is expected, and one is supposed to reload rules
+ via udevadm, which is the fix proposed in debian-installer-utils.
+ Removing the previous second test case that does not reload via udevadm.
  
  [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.
+ Additional calls to udevadm reload will cause all udev rules to be re-
+ read correctly. This may lead to new devices
+ discovered/configured/symlink during d-i installer, which were
+ previously skipped/missed.

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

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.

  The fix is to reload udevadm rules, as per upstream recommendation.

  [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.

  Stale context in udevd is expected, and one is supposed to reload
  rules via udevadm, which is the fix proposed in debian-installer-
  utils. Removing the previous second test case that does not reload via
  udevadm.

  [Regression Potential]

  Additional calls to udevadm reload will cause all udev rules to be re-
  read correctly. This may lead to new devices
  discovered/configured/symlink during d-i installer, which were
  previously skipped/missed.

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