Chapter 10. Keeping kernel panic parameters disabled in virtualized environments

A soft lockup usually indicates a bug. The affected task runs in kernel space on one CPU without rescheduling. The task also does not allow any other task to execute on that particular CPU.

As a result, a warning is displayed to a user through the system console. This problem is also referred to as the soft lockup firing.

Control system behavior during soft lockups by configuring certain kernel parameters. You can enable detection mechanisms, adjust thresholds, and determine if the kernel panics to manage system stability.

The soft lockup firing on physical hosts usually represents a kernel or a hardware bug. The same phenomenon happening on guest operating systems in virtualized environments might represent a false warning.

Heavy workload on a host or high contention over some specific resource, such as memory, can cause a spurious soft lockup firing because the host might schedule out the guest CPU for a period longer than 20 seconds. When the guest CPU is again scheduled to run on the host, it experiences a time jump that triggers the due timers. The timers also include the hrtimer watchdog that can report a soft lockup on the guest CPU.

Soft lockup in a virtualized environment can be false. You must not enable the kernel parameters that trigger a system panic when a soft lockup reports to a guest CPU.