3.10. Kernel

kernel component
Intel Xeon E5-XXXX V2 Series Processor running on the C600 chipset is not supported in Red Hat Enterprise Linux 6.3. An "unsupported hardware" message can therefore be reported by the kernel.
kernel component
The Red Hat Enterprise Linux 6.3 kernels upgraded the mlx4 modules to a later version. If the modules are used together with, for example, the HP InfiniBand Enablement Kit, the behavior is different. Consequently, certain Mellanox cards do not come up with network interfaces on Red Hat Enterprise Linux 6.3. To work around this problem, the mlx7_core module has to be loaded with the port_type_array option and a 2 parameter for each used InfiniBand card. Follow this example to manually load the driver for two cards in the system: 
~]# rmmod mlx4_en
~]# rmmod mlx4_core
~]# modprobe mlx4_core port_type_array=2,2
~]# modprobe mlx4_en
~]# ip a
The last of the above commands will show the new interfaces. To configure these parameters to be applied by the system when the modules are loaded, run: 
~]# echo 'options mlx4_core port_type_array=2,2' >/etc/modprobe.d/mlx4_core.conf
kernel component
When using Chelsio's iSCSI HBAs for an iSCSI root partition, the first boot after install fails. This occurs because Chelsio's iSCSI HBA is not properly detected. To work around this issue, users must add the iscsi_firmware parameter to grub's kernel command line. This will signal to dracut to boot from the iSCSI HBA.
kernel component
In Red Hat Enterprise Linux 6.3, three module parameters (num_lro, rss_mask, and rss_xor) that were supported by older versions of the mlx4_en driver have become obsolete and are no longer used. If you supply these parameters, the Red Hat Enterprise Linux 6.3 driver will ignore them and log a warning.
kernel component
Due to a race condition, in certain cases, writes to RAID4/5/6 while the array is reconstructing could hang the system.
kernel component
The installation of Red Hat Enterprise Linux 6.3 i386 may occasionally fail. To work around this issue, add the following parameter to the kernel command line: 
vmalloc=256MB
kernel component
If a device reports an error, while it is opened (via the open(2) system call), then the device is closed (via the close(2) system call), and the /dev/disk/by-id link for the device may be removed. When the problem on the device that caused the error is resolved, the by-id link is not re-created. To work around this issue, run the following command: 
~]# echo 'change' > /sys/class/block/sdX/uevent
kernel component
Platforms with BIOS/UEFI that are unaware of PCI-e SR-IOV capabilities may fail to enable virtual functions
kernel component
When an HBA that uses the mpt2sas driver is connected to a storage using an SAS switch LSI SAS 6160, the driver may become unresponsive during Controller Fail Drive Fail (CFDF) testing. This is due to faulty firmware that is present on the switch. To fix this issue, use a newer version (14.00.00.00 or later) of firmware for the LSI SAS 6160 switch.
kernel component, BZ#690523
If appropriate SCSI device handlers (scsi_dh modules) are not available when the storage driver (for example, lpfc) is first loaded, I/O operations may be issued to SCSI multipath devices that are not ready for those I/O operations. This can result in significant delays during system boot and excessive I/O error messages in the kernel log.
Provided the storage driver is loaded before multipathd is started (which is the default behavior), users can work around this issue by making sure the appropriate SCSI device handlers (scsi_dh modules) are available by specifying one of the following kernel command line parameters which dracut consumes: 
  • rdloaddriver=scsi_dh_emc

  • rdloaddriver=scsi_dh_rdac,scsi_dh_hp_sw

  • rdloaddriver=scsi_dh_emc,scsi_dh_rdac,scsi_dh_alua
Note that the order of the listed scsi_dh modules does not matter.
Specifying one of the above parameters causes the scsi_dh module(s) to load before the storage driver is loaded or multipath is started.
kernel component, BZ#745713
In some cases, Red Hat Enterprise Linux 6 guests running fully-virtualized under Red Hat Enterprise Linux 5 experience a time drift or fail to boot. In other cases, drifting may start after migration of the virtual machine to a host with different speed. This is due to limitations in the Red Hat Enterprise Linux 5 Xen hypervisor. To work around this, add the nohpet parameter or, alternatively, the clocksource=jiffies parameter to the kernel command line of the guest. Or, if running under Red Hat Enterprise Linux 5.7 or newer, locate the guest configuration file for the guest and add the hpet=0 parameter in it.
kernel component
On some systems, Xen full-virt guests may print the following message when booting: 
WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing <number>MB of RAM
It is possible to avoid the memory trimming by using the disable_mtrr_trim kernel command line option.
kernel component
The perf record command becomes unresponsive when specifying a tracepoint event and a hardware event at the same time.
kernel component
On 64-bit PowerPC, the following command may cause kernel panic: 
~]# ./perf record -agT -e sched:sched_switch -F 100 -- sleep 3
kernel component
Applications are increasingly using more than 1024 file descriptors. It is not recommended to increase the default soft limit of file descriptors because it may break applications that use the select() call. However, it is safe to increase the default hard limit; that way, applications requiring a large amount of file descriptors can increase their soft limit without needing root privileges and without any user intervention.
kernel component, BZ#770545
In Red Hat Enterprise Linux 6.2 and Red Hat Enterprise Linux 6.3, the default value for sysctl vm.zone_reclaim_mode is now 0, whereas in Red Hat Enterprise Linux 6.1 it was 1.
kernel component
Using Alsa with an HDA Intel sound card and the Conexant CX20585 codec causes sound and recording failures. To work around this issue, add the following line to the /etc/modprobe.d/dist-alsa.conf file: 
options snd-hda-intel model=thinkpad
kernel component
In network only use of Brocade Converged Network Adapters (CNAs), switches that are not properly configured to work with Brocade FCoE functionality can cause a continuous linkup/linkdown condition. This causes continuous messages on the host console: 
bfa xxxx:xx:xx.x: Base port (WWN = xx:xx:xx:xx:xx:xx:xx:xx) lost fabric connectivity
To work around this issue, unload the Brocade bfa driver.
kernel component
The lpfc driver is deprecating the sysfs mbox interface as it is no longer used by the Emulex tools. Reads and writes are now stubbed out and only return the -EPERM (Operation not permitted) symbol.
kernel component
In Red Hat Enterprise Linux 6, a legacy bug in the PowerEdge Expandable RAID Controller 5 (PERC5) which causes the kdump kernel to fail to scan for scsi devices. It is usually triggered when a large amounts of I/O operations are pending on the controller in the first kernel before performing a kdump.
kernel component, BZ#679262
In Red Hat Enterprise Linux 6.2 and later, due to security concerns, addresses in /proc/kallsyms and /proc/modules show all zeros when accessed by a non-root user.
kernel component
Superfluous information is displayed on the console due to a correctable machine check error occurring. This information can be safely ignored by the user. Machine check error reporting can be disabled by using the nomce kernel boot option, which disables machine check error reporting, or the mce=ignore_ce kernel boot option, which disables correctable machine check error reporting.
kernel component
The order in which PCI devices are scanned may change from one major Red Hat Enterprise Linux release to another. This may result in device names changing, for example, when upgrading from Red Hat Enterprise Linux 5 to 6. You must confirm that a device you refer to during installation, is the intended device.
One way to assure the correctness of device names is to, in some configurations, determine the mapping from the controller name to the controller's PCI address in the older release, and then compare this to the mapping in the newer release, to ensure that the device name is as expected.
The following is an example from /var/log/messages: 
kernel: cciss0: <0x3230> at PCI 0000:1f:00.0 IRQ 71 using DAC
…
kernel: cciss1: <0x3230> at PCI 0000:02:00.0 IRQ 75 using DAC
If the device name is incorrect, add the pci=bfsort parameter to the kernel command line, and check again.
kernel component
Enabling CHAP (Challenge-Handshake Authentication Protocol) on an iSCSI target for the be2iscsi driver results in kernel panic. To work around this issue, disable CHAP on the iSCSI target.
kernel component
Newer VPD (Vital Product Data) blocks can exceed the size the tg3 driver normally handles. As a result, some of the routines that operate on the VPD blocks may fail. For example, the nvram test fails when running the ethtool –t command on BCM5719 and BCM5720 Ethernet Controllers.
kernel component
Running the ethtool -t command on BCM5720 Ethernet controllers causes a loopback test failure because the tg3 driver does not wait long enough for a link.
kernel component
The tg3 driver in Red Hat Enterprise Linux 6.2 does not include support for Jumbo frames and TSO (TCP Segmentation Offloading) on BCM5719 Ethernet controllers. As a result, the following error message is returned when attempting to configure, for example, Jumbo frames: 
SIOCSIFMTU: Invalid argument
kernel component
The default interrupt configuration for the Emulex LPFC FC/FCoE driver has changed from INT-X to MSI-X. This is reflected by the lpfc_use_msi module parameter (in /sys/class/scsi_host/host#/lpfc_use_msi) being set to 2 by default, instead of the previous 0.
Two issues provide motivation for this change: SR-IOV capability only works with the MSI-X interrupt mode, and certain recent platforms only support MSI or MSI-X.
However, the change to the LPFC default interrupt mode can bring out host problems where MSI/MSI-X support is not fully functional. Other host problems can exist when running in the INT-X mode.
If any of the following symptoms occur after upgrading to, or installing Red Hat Enterprise Linux 6.2 with an Emulex LPFC adapter in the system, change the value of the lpfc module parameter, lpfc_use_msi, to 0:
  • The initialization or attachment of the lpfc adapter may fail with mailbox errors. As a result, the lpfc adapter is not configured on the system. The following message appear in /var/log/messages: 
    lpfc 0000:04:08.0: 0:0:0443 Adapter failed to set maximum DMA length mbxStatus x0
lpfc 0000:04:08.0: 0:0446 Adapter failed to init (255), mbxCmd x9 CFG_RING, mbxStatus x0, ring 0
lpfc 0000:04:08.0: 0:1477 Failed to set up hba
ACPI: PCI interrupt for device 0000:04:08.0 disabled
  • While the lpfc adapter is operating, it may fail with mailbox errors, resulting in the inability to access certain devices. The following message appear in /var/log/messages: 
    lpfc 0000:0d:00.0: 0:0310 Mailbox command x5 timeout Data: x0 x700 xffff81039ddd0a00
lpfc 0000:0d:00.0: 0:0345 Resetting board due to mailbox timeout
lpfc 0000:0d:00.0: 0:(0):2530 Mailbox command x23 cannot issue Data: xd00 x2
  • Performing a warm reboot causes any subsequent boots to halt or stop because the BIOS is detecting the lpfc adapter. The system BIOS logs the following messages: 
    Installing Emulex BIOS ......
Bringing the Link up, Please wait...
Bringing the Link up, Please wait...
kernel component
The minimum firmware version for NIC adapters managed by netxen_nic is 4.0.550. This includes the boot firmware which is flashed in option ROM on the adapter itself.
kernel component, BZ#683012
High stress on 64-bit IBM POWER series machines prevents kdump from successfully capturing the vmcore. As a result, the second kernel is not loaded, and the system becomes unresponsive.
kernel component
Triggering kdump to capture a vmcore through the network using the Intel 82575EB ethernet device in a 32 bit environment causes the networking driver to not function properly in the kdump kernel, and prevent the vmcore from being captured.
kernel component
Memory Type Range Register (MTRR) setup on some hyperthreaded machines may be incorrect following a suspend/resume cycle. This can cause graphics performance (specifically, scrolling) to slow considerably after a suspend/resume cycle.
To work around this issue, disable and then re-enable the hyperthreaded sibling CPUs around suspend/resume, for example: 
#!/bin/sh
# Disable hyper-threading processor cores on suspend and hibernate, re-enable
# on resume.
# This file goes into /etc/pm/sleep.d/

case $1 in
        hibernate|suspend)
                echo 0 > /sys/devices/system/cpu/cpu1/online
                echo 0 > /sys/devices/system/cpu/cpu3/online
                ;;

        thaw|resume)
                echo 1 > /sys/devices/system/cpu/cpu1/online
                echo 1 > /sys/devices/system/cpu/cpu3/online
                ;;
esac
kernel component
In Red Hat Enterprise Linux 6.2, nmi_watchdog registers with the perf subsystem. Consequently, during boot, the perf subsystem grabs control of the performance counter registers, blocking OProfile from working. To resolve this, either boot with the nmi_watchdog=0 kernel parameter set, or run the following command to disable it at run time: 
echo 0 > /proc/sys/kernel/nmi_watchdog
To re-enable nmi-watchdog, use the following command 
echo 1 > /proc/sys/kernel/nmi_watchdog
kernel component, BZ#603911
Due to the way ftrace works when modifying the code during start-up, the NMI watchdog causes too much noise and ftrace can not find a quiet period to instrument the code. Consequently, machines with more than 512 CPUs will encounter issues with the NMI watchdog. Such issues will return error messages similar to BUG: NMI Watchdog detected LOCKUP and have either ftrace_modify_code or ipi_handler in the backtrace. To work around this issue, disable NMI watchdog by setting the nmi_watchdog=0 kernel parameter, or using the following command at run time: 
echo 0 > /proc/sys/kernel/nmi_watchdog
kernel component
On 64-bit POWER systems the EHEA NIC driver will fail when attempting to dump a vmcore via NFS. To work around this issue, utilize other kdump facilities, for example dumping to the local file system, or dumping over SSH.
kernel component, BZ#587909
A BIOS emulated floppy disk might cause the installation or kernel boot process to hang. To avoid this, disable emulated floppy disk support in the BIOS.
kernel component
The preferred method to enable nmi_watchdog on 32-bit x86 systems is to use either nmi_watchdog=2 or nmi_watchdog=lapic parameters. The parameter nmi_watchdog=1 is not supported.
kernel component
The kernel parameter, pci=noioapicquirk, is required when installing the 32-bit variant of Red Hat Enterprise Linux 6 on HP xw9300 workstations. Note that the parameter change is not required when installing the 64-bit variant.