<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> <HTML ><HEAD ><TITLE >Recipes for Deadlock</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Unreliable Guide To Hacking The Linux Kernel" HREF="book1.html"><LINK REL="PREVIOUS" TITLE="ioctls: Not writing a new system call" HREF="c108.html"><LINK REL="NEXT" TITLE="Common Routines" HREF="c141.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Unreliable Guide To Hacking The Linux Kernel</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c108.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="c141.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="DEADLOCK-RECIPES" ></A >Recipes for Deadlock</H1 ><P > You cannot call any routines which may sleep, unless: </P ><P ></P ><UL ><LI ><P > You are in user context. </P ></LI ><LI ><P > You do not own any spinlocks. </P ></LI ><LI ><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 ><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 will eventually lock up your box if you break these rules. </P ><P > Really. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="c108.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="book1.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="c141.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >ioctls: Not writing a new system call</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Common Routines</TD ></TR ></TABLE ></DIV ></BODY ></HTML >