mountall assert failure: mountall.c:1411: Assertion failed in skip_mount: (! mnt->mounted) || needs_remount (mnt)

StacktraceTop:
 __kernel_vsyscall ()
 *__GI_raise (sig=6)
 *__GI_abort () at abort.c:92
 skip_mount (mnt=0x21bebf98) at mountall.c:1411
 plymouth_update (only_clear=0) at mountall.c:2892

I've never seen this bug in the wild, but there are several crash reports for it on errors.ubuntu.com, across multiple versions of mountall:

https://errors.ubuntu.com/problem/f3f277839135e7752563c03c124625f5873c8941
https://errors.ubuntu.com/problem/932d8371391257ab50448f9433fd401bcc1bef61
https://errors.ubuntu.com/problem/954d2e870a58368e05eca7522954a61dd6774af7

Status changed to 'Confirmed' because the bug affects multiple users.

This bug was fixed in the package mountall - 2.50

---------------
mountall (2.50) unstable; urgency=low

  * Add support for pstore. Closes: #722212.
  * Allow multiple fstab entries with the same mountpoint: we still mask
    any entries that came from a different source (i.e., /etc/fstab will
    mask /lib/init/fstab), but if there are multiple entries in /etc/fstab,
    treat them all as separate mounts instead of letting the last one win.
    LP: #503003.
  * Don't set 'console output' anymore; now that we have upstart logging by
    default, logs will be captured and (assuming /var/log becomes writable
    at some point) mountall is debuggable without having to spew text to the
    console.
  * Support reading --verbose/--debug options from /proc/cmdline, so that
    we can give users a better way to debug mountall without having to
    edit the upstart job.
  * Since everything is in a single event loop, a request from plymouth to
    skip a mount may come in after the mount has already happened. So don't
    assert on a bogus request, just treat it as a no-op and continue.
    LP: #731800.

 -- Steve Langasek <email address hidden> Tue, 10 Sep 2013 04:01:19 +0000