Book Image

Linux Kernel Debugging

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Debugging

By: Kaiwan N. Billimoria

Overview of this book

The Linux kernel is at the very core of arguably the world’s best production-quality OS. Debugging it, though, can be a complex endeavor. Linux Kernel Debugging is a comprehensive guide to learning all about advanced kernel debugging. This book covers many areas in-depth, such as instrumentation-based debugging techniques (printk and the dynamic debug framework), and shows you how to use Kprobes. Memory-related bugs tend to be a nightmare – two chapters are packed with tools and techniques devoted to debugging them. When the kernel gifts you an Oops, how exactly do you interpret it to be able to debug the underlying issue? We’ve got you covered. Concurrency tends to be an inherently complex topic, so a chapter on lock debugging will help you to learn precisely what data races are, including using KCSAN to detect them. Some thorny issues, both debug- and performance-wise, require detailed kernel-level tracing; you’ll learn to wield the impressive power of Ftrace and its frontends. You’ll also discover how to handle kernel lockups, hangs, and the dreaded kernel panic, as well as leverage the venerable GDB tool within the kernel (KGDB), along with much more. By the end of this book, you will have at your disposal a wide range of powerful kernel debugging tools and techniques, along with a keen sense of when to use which.
Table of Contents (17 chapters)
1
Part 1: A General Introduction and Approaches to Kernel Debugging
4
Part 2: Kernel and Driver Debugging Tools and Techniques
11
Part 3: Additional Kernel Debugging Tools and Techniques

Employing the kernel's hung task and workqueue stall detectors

A hung task is one that's become unresponsive. Similarly, the kernel can also, on occasion, suffer from some types of stalls (workqueue and RCU). In this section, we will examine how we can leverage these features, allowing us to detect them so that an action – such as triggering a panic or emitting a warning with stack backtraces – can be taken. Obviously, the warnings logged can then help you, the developer, understand what occurred and work to fix it.

Leveraging the kernel hung task detector

Configuring the kernel via the usual make menuconfig UI, under the Kernel hacking | Debug Oops, Lockups and Hangs menu (refer to Figure 10.8), you'll find entries labeled as follows:

[*] Detect Hung Tasks
(120) Default timeout for hung task detection (in seconds)
[ ]   Panic (Reboot) On Hung Tasks

These are what we discuss here. The whole idea, when enabled, is to allow...