RHBA-2012:1310 - Bug Fix Advisory

Topic

Updated kernel packages that fix several bugs and add an enhancement are now
available for Red Hat Enterprise Linux 6 Extended Update Support.

[Updated 23 Oct 2012]
This advisory has been updated with an accurate value of the clock drift for
BZ#853951 (+/- 20 MHz). This update does not change the packages in any way.

Description

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

This update fixes the following bugs:

• Prior to this update, the find_busiest_group() function used

sched_group->cpu_power in the denominator of a fraction with a value of 0.
Consequently, a kernel panic occurred. This update prevents the divide by zero
in the kernel and the panic no longer occurs. (BZ#844943)

• Previously, the TCP socket bound to NFS server contained a stale skb_hints

socket buffer. Consequently, kernel could terminate unexpectedly. A patch has
been provided to address this issue and skb_hints is now properly cleared from
the socket, thus preventing this bug. (BZ#846830)

• Previously, when a server attempted to shut down a socket, the

svc_tcp_sendto() function set the XPT_CLOSE variable if the entire reply failed
to be transmitted. However, before XPT_CLOSE could be acted upon, other threads
could send further replies before the socket was really shut down. Consequently,
data corruption could occur in the RPC record marker. With this update, send
operations on a closed socket are stopped immediately, thus preventing this bug.
(BZ#853255)

• When a PIT (Programmable Interval Timer) MSB (Most Significant Byte)

transition occurred very close to an SMI (System Management Interrupt)
execution, the pit_verify_msb() function did not see the MSB transition.
Consequently, the pit_expect_msb() function returned success incorrectly,
eventually causing a large clock drift in the quick_pit_calibrate() function. As
a result, the TSC (Time Stamp Counter) calibration on some systems was off by
+/- 20 MHz, which led to inaccurate timekeeping or ntp synchronization failures.
This update fixes pit_expect_msb() and the clock drift no longer occurs in the
described scenario. (BZ#853951)

This update adds the following enhancement:

• This update adds support for the Proportional Rate Reduction (PRR) algorithms

for the TCP protocol. This algorithm determines TCP's sending rate in fast
recovery. PRR avoids excessive window reductions and improves accuracy of the
amount of data sent during loss recovery. In addition, a number of other
enhancements and bug fixes for TCP are part of this update. (BZ#847731)

All users are advised to upgrade to these updated packages, which fix these bugs
and add this enhancement. 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 6.1 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.1 i386
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.1 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.1 ppc64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.1 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.1 i386
• Red Hat Virtual Storage Appliance (from RHUI) 6.1 x86_64

Fixes

CVEs

(none)

References

(none)