RHBA-2012:1198 - Bug Fix Advisory

Topic

Updated kernel packages that fix two bugs are now available for Red Hat
Enterprise Linux 6 Extended Update Support.

Description

The kernel packages contain the Linux kernel, the core of any Linux operating
system.

When an NTP server asserts the STA_INS flag (Leap Second Insert), the kernel
starts an hrtimer (high-resolution timer) with a countdown clock. This hrtimer
expires at end of the current month, midnight UTC, and inserts a second into the
kernel timekeeping structures. A scheduled leap second occurred on June 30 2012
midnight UTC.

This update fixes the following bugs:

• Previously in the kernel, when the leap second hrtimer was started, it was

possible that the kernel livelocked on the xtime_lock variable. This update
fixes the problem by using a mixture of separate subsystem locks (timekeeping
and ntp) and removing the xtime_lock variable, thus avoiding the livelock
scenarios that could occur in the kernel. (BZ#840949)

• After the leap second was inserted, applications calling system calls that

used futexes consumed almost 100% of available CPU time. This occurred because
the kernel's timekeeping structure update did not properly update these futexes.
The futexes repeatedly expired, re-armed, and then expired immediately again.
This update fixes the problem by properly updating the futex expiration times by
calling the clock_was_set_delayed() function, an interrupt-safe method of the
clock_was_set() function. (BZ#847365)

All users are advised to upgrade to these updated packages, which fix these
bugs. The system must be rebooted for this update to take effect.

Solution

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/knowledge/articles/11258

Affected Products

• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 i386
• Red Hat Enterprise Linux Server - AUS 6.2 x86_64
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.2 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.2 ppc64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 i386
• Red Hat Storage 2.0 x86_64
• Red Hat Gluster Storage Server for On-premise 2.0 x86_64
• Red Hat Storage for Public Cloud (via RHUI) 2.0 x86_64

Fixes

• BZ - 840949 - livelock in leapsecond insertion [rhel-6.2.z]

CVEs

(none)

References

(none)