Red Hat ENTERPRISE LINUX 5.5 - TECHNICAL NOTES Manual page 324

Chapter 5. Known Issues
If the kmod-kvm package is installed, the 'kvm_intel' or 'kvm_amd' module automatically loads
during boot on some systems. If a physical CPU is placed offline while the 'kvm_intel' or 'kvm_amd'
module is loaded a subsequent attempt to online that CPU may fail with an I/O error.
To work around this issue, unload the 'kvm_intel' or 'kvm_amd' before performing physical CPU hot-
plug operations. It may be necessary to shut down KVM guests before the 'kvm_intel' or 'kvm_amd'
will successfully unload.
For example, to offline a physical CPU 6 on an Intel based system:
# rmmod kvm_intel
# echo 0 > -/sys/devices/system/cpu/cpu6/online
# modprobe kvm_intel
66
(BZ#515557)
• A change to the cciss driver in Red Hat Enterprise Linux 5.4 made it incompatible with the "echo
disk > /sys/power/state" suspend-to-disk operation. Consequently, the system will not suspend
properly, returning messages such as:
Stopping tasks:
======================================================================
stopping tasks timed out after 20 seconds (1 tasks remaining):
cciss_scan00
Restarting tasks...<6> Strange, cciss_scan00 not stopped
done
67
(BZ#513472)
• The kernel is unable to properly detect whether there is media present in a CD-ROM drive during
kickstart installs. The function to check the presence of media incorrectly interprets the "logical unit
is becoming ready" sense, returning that the drive is ready when it is not. To work around this issue,
wait several seconds between inserting a CD and asking the installer (anaconda) to refresh the CD.
68
(BZ#510632)
• When a cciss device is under high I/O load, the kdump kernel may panic and the vmcore dump may
not be saved successfully.
• Applications attempting to malloc memory approximately larger than the size of the physical
memory on the node on a NUMA system may hang or appear to stall. This issue may occur on a
NUMA system where the remote memory distance, as defined in SLIT, is greater than 20 and RAM
based filesystem like tmpfs or ramfs is mounted.
To work around this issue, unmount all RAM based filesystems (i.e. tmpfs or ramfs). If unmounting
the RAM based filesystems is not possible, modify the application to allocate lesser memory. Finally,
if modifying the application is not possible, disable NUMA memory reclaim by running:
sysctl vm.zone_reclaim_mode=0
314
69
(BZ#509790)