touch-packages team mailing list archive

[Brian Murray <brian@xxxxxxxxxx>]

Hello Thomas, or anyone else affected,

Accepted ntp into precise-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/ntp/1:4.2.6.p3+dfsg-
1ubuntu3.8 in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to
enable and use -proposed.  Your feedback will aid us getting this update
out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to ntp in Ubuntu.
https://bugs.launchpad.net/bugs/1125726

Title:
  boot-time race between /etc/network/if-up.d/ntpdate and
  "/etc/init.d/ntp start"

Status in ntp package in Ubuntu:
  Fix Released
Status in ntp source package in Precise:
  Fix Committed
Status in ntp source package in Trusty:
  Fix Committed

Bug description:
  [Impact] 
  * Hardware clocks are not stepped at boot, which can prevent NTP from ever
    syncing the clock.
    Incorrect clocks can cause serious issues in distributed systems.

  * Upstream originally added a lock file to eliminate a race between the ntp
    service (which keeps the clock synchronized during normal operation) and
    ntpdate (which is used to step the clock by large intervals at boot time).
    That change had a flaw which introduced a deadlock. An Ubuntu patch was
    applied which broke the locking mechanism entirely, reintroducing the race
    condition.

  * This change undoes the Ubuntu patch and fixes the deadlock by unlocking
    before attempting to start the ntp service.

  [Test Case]

  * There are two bugs: The race, and the deadlock. To reproduce the race more
    consistently:
    - add 'sleep 30' to '/etc/network/if-up.d/ntpdate' on the line preceding
      '/usr/sbin/ntpdate-debian -s $OPTS 2>/dev/null || :', and comment out
      'invoke-rc.d --quiet $service stop >/dev/null 2>&1 || true'. This will
      reproduce the case where the ntp service starts between the stop command
      and the ntpdate command.
      The result will be that the ntpdate command fails. There will be a
      message in syslog like:
        'ntpdate[17660]: the NTP socket is in use, exiting'
    - Reintroducing the lock brings back the deadlock issue. Both the ntpdate
      if-up.d script and the ntp init script check the lock file, but the
      ntpdate script attempted to start the ntp init script before unlocking
      the lock. Moving the unlock before the init script invocation fixes
      the deadlock. The original deadlock behavior is described here:
        https://bugs.launchpad.net/ubuntu/+source/ntp/+bug/246203

  [Regression Potential]

  * Low. Out-of-sync clocks could be changed a large amount at boot time, but
    only for machines with static IP's. The clock is only likely to be in this
    state if the clock was very skewed at boot time, which is also unlikely
    since NTP usually keeps the software clock in sync during operation and
    the hardware clock is updated at shutdown.

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