'\" t
.\"     Title: wake_up_bit
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: May 2018
.\"    Manual: Driver Basics
.\"    Source: Kernel Hackers Manual 3.16.56
.\"  Language: English
.\"
.TH "WAKE_UP_BIT" "9" "May 2018" "Kernel Hackers Manual 3\&.16\&" "Driver Basics"
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.SH "NAME"
wake_up_bit \- wake up a waiter on a bit
.SH "SYNOPSIS"
.HP \w'void\ wake_up_bit('u
.BI "void wake_up_bit(void\ *\ " "word" ", int\ " "bit" ");"
.SH "ARGUMENTS"
.PP
\fIword\fR
.RS 4
the word being waited on, a kernel virtual address
.RE
.PP
\fIbit\fR
.RS 4
the bit of the word being waited on
.RE
.SH "DESCRIPTION"
.PP
There is a standard hashed waitqueue table for generic use\&. This is the part of the hashtable\*(Aqs accessor API that wakes up waiters on a bit\&. For instance, if one were to have waiters on a bitflag, one would call
\fBwake_up_bit\fR
after clearing the bit\&.
.PP
In order for this to function properly, as it uses
\fBwaitqueue_active\fR
internally, some kind of memory barrier must be done prior to calling this\&. Typically, this will be
\fBsmp_mb__after_atomic\fR, but in some cases where bitflags are manipulated non\-atomically under a lock, one may need to use a less regular barrier, such fs/inode\&.c\*(Aqs
\fBsmp_mb\fR, because
\fBspin_unlock\fR
does not guarantee a memory barrier\&.
.SH "COPYRIGHT"
.br