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

Summary

Congratulations on completing this chapter! By now, you should have your own custom panic handler reading and raring to go!

To quickly summarize, in this chapter, we covered what a kernel panic is, interpreted its log output, and importantly, learned how to leverage the kernel's powerful notifier chain infrastructure to develop our own custom kernel panic handler.

We then moved on to what kernel lockup – hard, soft, and RCU CPU stalls – means and how to configure the kernel to detect it (with small examples to show what it looks like when it locks up!). The final section covered how to detect hung tasks (unresponsive tasks that remain in the D state for a long while) and workqueue stalls.

Once issues like this are detected, examining the kernel log (where, typically, you'll have the kernel warning and CPU backtraces) can provide you with valuable clues as to where an issue lies, thus helping you fix it.

I'll see you in the next chapter...