This library provides instrumentation for detecting when the kernel has remained in a critical section for “too long”. Critical sections are marked using LOCKUP_BEGIN() and LOCKUP_END(). The code executing under a spinlock is an example of a critical section. A function that temporarily disables interrupts would be another example.
Currently, detection is performed only when a CPU leaves a critical section (calls LOCKUP_END()). If a CPU calls LOCKUP_BEGIN(), but never calls LOCKUP_END(), the instrumentation will not detect the “lockup”. However, there is a k command that can be used to check if a CPU is currently in a critical section: k lockup status. This command is intended to be used as an interactive diagnostic tool.
Choosing an appropriate lockup threshold is important. The value should be small enough to detect performance impacting lockups, but large enough to avoid false alarms, especially when running on virtualized hardware.
See also kernel.lockup-detector.threshold-ms.
A future version of this library may add instrumentation for detecting when a CPU has been “executing kernel code for too long”, or has been in a hypervisor or Secure Monitor call for too long. A future version may also integrate with a software watchdog to take corrective action when lockups are detected.