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5.1. All Architectures

  • relayfs previously had a buffer size limit of 64MB. In this update, the limitation of the memory allocated to relayfs for on-memory buffers has been increased to 4095MB. This allows SystemTap and other tracing tools that utilize relayfs the ability to trace more events.
  • The driver for Dell Remote Access Controller 4 (DRAC4) was not present. Consequently, any virtual devices provided by the DRAC4 were not being detected by the kernel. In this update, the pata_sil680 kernel module that provides the appropriate driver has been added, which resolves this issue.
  • The message buffers for the relay interface were only allocated for online CPUs when relay_open() was called. Consequently, if an off-line CPU was turned on after relay_open() was called, a kernel panic would occur. In this update, a new message buffer is allocated dynamically if any new CPUs are added.
  • The driver for 8250 based serial ports has been updated to add support for DSR/DTR hardware flow control.
  • Support for Dell Wireless Wide Area Network (WWAN) cards has been added to the kernel. Devices that are now supported are:
    • Dell Wireless 5700 Mobile Broadband CDMA/EVDO Mini-Card
    • Dell Wireless 5500 Mobile Broadband HSDPA Mini-Card
    • Dell Wireless 5505 Mobile Broadband HSDPA Mini-Card
    • Dell Wireless 5700 Mobile Broadband CDMA/EVDO ExpressCard
    • Dell Wireless 5510 Mobile Broadband HSDPA ExpressCard
    • Dell Wireless 5700 Mobile Broadband CDMA/EVDO Mini-Card
    • Dell Wireless 5700 Mobile Broadband CDMA/EVDO Mini-Card
    • Dell Wireless 5720
    • Dell Wireless HSDPA 5520
    • Dell Wireless HSDPA 5520
    • Dell Wireless 5520 Voda I Mobile Broadband (3G HSDPA) Mini-Card
  • the thinkpad_acpi kernel module has been updated to provide enhanced support for newer Thinkpad models.
  • The soft lockup detector can now be configured to trigger a kernel panic instead of a warning message. This makes it possible for users to generate and analyze a crash dump during a soft lockup for forensic purposes.
    To configure the soft lockup detector to generate a panic, set the kernel parameter soft_lockup to 1. This parameter is set to 0 by default.
  • oprofile did not correctly identify processors based on the Next-Generation Intel Microarchitecture (Nehalem). Consequently, the performance monitoring unit could not be used and the processor fell back to the timer interrupt. The kernel has been updated to resolve this issue.
  • Support has been added to the kernel for the CPU power state, C3, on the Next-Generation Intel Microarchitecture (Nehalem). The ability to enter C3 (also known as the sleep state) improves the power efficiency of the CPU when idle.
  • Previously, the MAX_ARG_PAGES limit that is set in the kernel was too low, and may have resulted in the following error:
    execve: Argument list too long
    
    In this update, this limit has been increased to 25 percent of the stack size, which resolves this issue.
  • autofs4 updates have been backported to Red Hat Enterprise Linux 5.3 from linux kernel version 2.6.27.
  • Red Hat Enterprise Linux 5.3 now includes the ability to specify that core files be piped to a forked copy of a user space application, rather than directly to a file. This is enabled by placing | path/to/applicationin /proc/sys/kernel/core_pattern. When a core is dumped, a copy of the specified application will be executed, and the core will be piped to it on stdin. This allows for the core to be augmented, analyzed and actively handled at core dump time.
  • The file /proc/cpuinfo now reports the ID of the Advanced Programmable Interrupt Controller (APIC) that is used by each individual CPU.
  • The Machine Check Exception (MCE) kernel subsystem has been enhanced to support larger memory configurations as needed by new systems.
  • The mount command now supports Kerberos authentication when mounting filesystems via Samba. The sec=krb5 or sec=krb5i switch allows the kernel to call a userspace application (cifs.upcall) which returns a SPNEGO (Simple and Protected GSSAPI Negotiation Mechanism) security blob (Binary Large OBject). The kernel can then use this blob to authenticate with the server and mount the requested filesystem.
  • If you configured the kernel parameter kernel.unknown_nmi_panic on a system that used the IOAPIC NMI watchdog method, a kernel panic could occur. This is because the NMI watchdog could not disable the source of NMIs securely.
    With this release, the NMI watchdog code has been revised to allow users to safely disable the NMI source. As such, you can now safely configure the kernel parameter kernel.unknown_nmi_panic on systems that use the IOAPIC NMI watchdog method.

5.2. x86 Architectures

  • The powernowk8 driver was not performing sufficient checks on the number of running CPUs. Consequently, when the driver was started, a kernel oops error message may have been reported. In this update the powernowk8 driver verifies that the number of supported CPUs (supported_cpus) equals the number of online CPUs (num_online_cpus), which resolves this issue.

5.3. PowerPC Architectures

  • CPUFreq, the kernel subsystem that scales CPU frequency and voltage, has been updated with improved support for Cell Processors. This update implements a Synergistic Processing Unit (SPU) aware CPUFreq governor that enhances the power management of Cell processors.
  • Error Detection and Correction (EDAC) is now supported on the Cell Broadband Engine Architecture in Red Hat Enterprise Linux 5.3. To enable EDAC, use the command: modprobe cell_edac
    To check this module has been added to your running kernel, check /var/log/dmesg for output like the following:
    EDAC MC: Ver: 2.0.1 Oct  4 2008
    EDAC MC0: Giving out device to cell_edac MIC: DEV cbe-mic
    EDAC MC1: Giving out device to cell_edac MIC: DEV cbe-mic
    
    If correctable memory errors are encountered, the following message will be returned to the console:
    EDAC MC0: CE page 0xeff, offset 0x5700, grain 0, syndrome 0x51, row 0, channel
    0, label "":
    
  • Debugging with hardware watchpoints using a variable that is shared between multiple threads was causing the GNU Debugger (GDB) to erratically miss trigger events. The kernel has been updated to allow GDB to consistently receive the watchpoint triggers, improving the reliability of the debugging session.

5.4. x86_64 Architectures

  • kprobe-booster is now supported on the ia64 and x86_64 architectures, allowing users to probe kernel events much faster. This feature will also decrease the overhead caused by probing tools (e.g. SystemTap and Kprobes) on servers running on 64-bit architecture.
  • Support has been added to the kernel for the _PTC (Processor Throttling Control), _TSS (Throttling Supported States) and _TPC (Throttling Present Capabilities) objects. This support, which is part of the Advance Configuration and Power Interface specification (ACPI) provides improved management of processor throttling.

5.5. s390x Architectures

  • In zipl.conf, parameters enclosed with double quotes inside of single quotes (ie parameters='vmhalt="LOGOFF"') were being parsed incorrectly. Consequently, installing the kernel-kdump package may have failed, resulting in the error:
    grubby fatal error: unable to find a suitable template
    
    To resolve this issue, parameters should be enclosed with single quotes inside of double quotes (ie parameters="vmhalt='LOGOFF'")

    Note

    The syntax structure of single quotes inside of double quotes is the default in Red hat Enterprise Linux 5.

5.6. ia64 Architecture

  • The Dual-Core Intel Itanium 2 processor filled out machine check architecture (MCA) records differently to previous Intel Itanium processors. The cache check and bus check target identifiers can now be different in some circumstances. The kernel has been updated to find the correct target identifier.
  • kprobe-booster is now supported on the ia64 and x86_64 architectures, allowing users to probe kernel events much faster. This feature will also decrease the overhead caused by probing tools (e.g. SystemTap and Kprobes) on servers running on 64-bit architecture.
  • In this update, support for pselect() and ppoll() system calls has been added to the kernel.

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