<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 5. Recipes for Deadlock</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel" /><link rel="up" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel" /><link rel="prev" href="ch04.html" title="Chapter 4. ioctls: Not writing a new system call" /><link rel="next" href="ch06.html" title="Chapter 6. Common Routines" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 5. Recipes for Deadlock</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch06.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 5. Recipes for Deadlock"><div class="titlepage"><div><div><h2 class="title"><a id="deadlock-recipes"></a>Chapter 5. Recipes for Deadlock</h2></div></div></div><p>
You cannot call any routines which may sleep, unless:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
You are in user context.
</p></li><li class="listitem"><p>
You do not own any spinlocks.
</p></li><li class="listitem"><p>
You have interrupts enabled (actually, Andi Kleen says
that the scheduling code will enable them for you, but
that's probably not what you wanted).
</p></li></ul></div><p>
Note that some functions may sleep implicitly: common ones are
the user space access functions (*_user) and memory allocation
functions without <span class="symbol">GFP_ATOMIC</span>.
</p><p>
You should always compile your kernel
<span class="symbol">CONFIG_DEBUG_SPINLOCK_SLEEP</span> on, and it will warn
you if you break these rules. If you <span class="emphasis"><em>do</em></span> break
the rules, you will eventually lock up your box.
</p><p>
Really.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch06.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 4. ioctls: Not writing a new system call </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 6. Common Routines</td></tr></table></div></body></html>
