1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>wake_up_bit</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Linux Device Drivers"><link rel="up" href="ch01s04.html" title="Wait queues and Wake events"><link rel="prev" href="API-abort-exclusive-wait.html" title="abort_exclusive_wait"><link rel="next" href="API-wake-up-atomic-t.html" title="wake_up_atomic_t"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">wake_up_bit</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-abort-exclusive-wait.html">Prev</a>&#160;</td><th width="60%" align="center">Wait queues and Wake events</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-wake-up-atomic-t.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-wake-up-bit"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>wake_up_bit &#8212; 
2     wake up a waiter on a bit
3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <b class="fsfunc">wake_up_bit </b>(</code></td><td>void * <var class="pdparam">word</var>, </td></tr><tr><td>&#160;</td><td>int <var class="pdparam">bit</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1107467204"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>word</code></em></span></dt><dd><p>
4     the word being waited on, a kernel virtual address
5    </p></dd><dt><span class="term"><em class="parameter"><code>bit</code></em></span></dt><dd><p>
6     the bit of the word being waited on
7    </p></dd></dl></div></div><div class="refsect1"><a name="idp1107469812"></a><h2>Description</h2><p>
8   There is a standard hashed waitqueue table for generic use. This
9   is the part of the hashtable's accessor API that wakes up waiters
10   on a bit. For instance, if one were to have waiters on a bitflag,
11   one would call <code class="function">wake_up_bit</code> after clearing the bit.
12   </p><p>
13
14   In order for this to function properly, as it uses <code class="function">waitqueue_active</code>
15   internally, some kind of memory barrier must be done prior to calling
16   this. Typically, this will be <code class="function">smp_mb__after_atomic</code>, but in some
17   cases where bitflags are manipulated non-atomically under a lock, one
18   may need to use a less regular barrier, such fs/inode.c's <code class="function">smp_mb</code>,
19   because <code class="function">spin_unlock</code> does not guarantee a memory barrier.
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