Unreliable Guide To Locking

Paul Rusty Russell

rusty@rustcorp.com.au

Copyright © 2000 by Paul Russell

Table of Contents

1. Introduction

The Problem With Concurrency

2. Two Main Types of Kernel Locks: Spinlocks and Semaphores

Locks and Uniprocessor Kernels

Read/Write Lock Variants

Locking Only In User Context

Locking Between User Context and BHs

Locking Between User Context and Tasklets/Soft IRQs

Locking Between Bottom Halves

The Same BH
Different BHs

Locking Between Tasklets

The Same Tasklet
Different Tasklets

Locking Between Softirqs

The Same Softirq
Different Softirqs

3. Hard IRQ Context

Locking Between Hard IRQ and Softirqs/Tasklets/BHs

4. Common Techniques

No Writers in Interrupt Context

Deadlock: Simple and Advanced

Preventing Deadlock
Overzealous Prevention Of Deadlocks

Per-CPU Data

Big Reader Locks

Avoiding Locks: Read And Write Ordering

Avoiding Locks: Atomic Operations

Protecting A Collection of Objects: Reference Counts

Macros To Help You

Things Which Sleep

The Fucked Up Sparc

Racing Timers: A Kernel Pastime

5. Further reading

List of Tables
1-1. Expected Results
1-2. Possible Results
4-1. Consequences

		Next
		Introduction