[systemd-bugs] [Bug 79283] New: Commit "udev: remove seqnum API and all assumptions about seqnums" causes single CPU systems to fail to boot with debug kernels

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79283

          Priority: medium
            Bug ID: 79283
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: Commit "udev: remove seqnum API and all assumptions
                    about seqnums" causes single CPU systems to fail to
                    boot with debug kernels
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: blocker
    Classification: Unclassified
                OS: All
          Reporter: awilliam at redhat.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

This bug was identified downstream in Fedora Rawhide, but seems sufficiently
serious to merit alerting upstream to directly.

Commit
http://cgit.freedesktop.org/systemd/systemd/commit/?id=9ea28c55a2488e6cd4a44ac5786f12b71ad5bc9f
- "udev: remove seqnum API and all assumptions about seqnums" - was backported
to Fedora Rawhide's systemd 212 build as the sole change between
systemd-212-3.fc21 and systemd-212-4.fc21 . After that change, multiple users
reported that systems with single processors no longer booted correctly. Myself
and Josh Boyer (Fedora kernel maintainer) both confirmed this issue. It seems
to be some kind of race, as it only occurs with kernels that have debugging
code enabled.

With a Fedora live image that has systemd-212-4 and a debug kernel - e,g,
http://kojipkgs.fedoraproject.org/work/tasks/1167/6891167/Fedora-Live-Xfce-x86_64-rawhide-20140526.iso
- system boot fails every single time (tried six times, got six fails) in a KVM
with a single CPU, for me.

I built a systemd-212-5 package with the change from -4 reverted, and built a
live image with that systemd but which was otherwise the same as the Xfce
nightly linked above), and booted that five times; it worked every time.

So, there seems to be strong evidence that this commit causes a major problem
in this case (single CPU system, debug kernel).

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