Public bug reported:
[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correctly, it is not acceptable for it to use an out of date module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-udevd kmod builtin does not find NVMe pci modalias because its context is out
of date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.
** Affects: systemd (Ubuntu)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Changed in: systemd (Ubuntu)
Status: New => In Progress
** Changed in: systemd (Ubuntu)
Importance: Undecided => Medium
** Changed in: systemd (Ubuntu)
Assignee: (unassigned) => Dan Streetman (ddstreet)
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https://bugs.launchpad.net/bugs/1714505
Title:
systemd kmod builtin uses out of date kmod context
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