Chapter 10. Keeping kernel panic parameters disabled in virtualized environments

A soft lockup occurs when a task executes in kernel space without rescheduling, preventing other tasks from running on that CPU. This issue, often caused by a bug, triggers a warning on the system console to alert users.

The following kernel parameters can be set to control a system’s behavior when a soft lockup is detected.

Soft lockup warnings on guest operating systems can be false alarms caused by host workload or resource contention. Unlike physical hosts where these indicate bugs, virtualized environments might trigger false warnings when the host schedules out the guest CPU for extended periods.

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.