** 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correctly, it is not acceptable for it to use an out of date module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out of date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
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