Red Hat Bugzilla – Bug 457702
udev creates hwclock race in system with multiple RTC devices
Last modified: 2014-03-16 23:15:31 EDT
In a system with multiple RTC devices, udev executes '/sbin/hwclock --hctosys' multiple times in such a way that it creates a race condition. (System load > 2.9 on a dual-core Athlon).
Observed behavior is a hang at udev startup (eventually times out and boot continues with udev still working in the background). Once logged in, executing 'top' reveals at least two 'hwclock' processes using up all available processor time. Prior to killing all 'hwclock' instances, system response is very sluggish.
NOTE: This may be related to specific hardware and/or the DVB subsystem; the additional RTCs in the affected system are on two similar DVB capture cards:
- Dvico FusionHDTV 5 Gold (pci)
- Dvico FusionHDTV 5 Express (pci-e)
This problem was not noticed on Fedora 7 with a pre-2.6.24 kernel, but that's probably because the PCI-E card was not supported nor initialized under that kernel.
This problem was observed using the Fedora 9 release kernel as well as a fully updated system as of 03 Aug 2008 (kernel 220.127.116.11-97.fc9.x86_64).
Version-Release: Fedora 9 (Sulphur)
How reproducible: 100%, under above conditions
Replacing '/etc/udev/rules.d/88-clock.rules' with the following successfully prevented the 'hwclock' race condition:
# First RTC
ACTION=="add", SUBSYSTEM=="rtc", NAME=="rtc0", RUN+="/sbin/hwclock --hctosys --rtc=/dev/%k"
ACTION=="add", MAJOR==10, MINOR==135, NAME=="rtc0", RUN+="/sbin/hwclock --hctosys --rtc=/dev/%k"
# Additional RTCs
ACTION=="add", SUBSYSTEM=="rtc", NAME=="rtc[1-9][0-9]*"
ACTION=="add", MAJOR==10, MINOR==135, NAME=="rtc[1-9][0-9]*"
This is my first time troubleshooting udev and I don't know enough about the uses of the RTC subsystem to know if this change would cause adverse effects.
$ rpm -qf /etc/udev/rules.d/88-clock.rules
What are the hung processes actually doing (check with strace, etc.)
Considering that they're supposed to be called to operate on different devices, I'm not sure why they would fail in that way.b
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