'\" t
.\"     Title: __test_and_clear_bit
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Basic C Library Functions
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "__TEST_AND_CLEAR_BIT" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Basic C Library Functions"
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.SH "NAME"
__test_and_clear_bit \- Clear a bit and return its old value
.SH "SYNOPSIS"
.HP \w'bool\ __test_and_clear_bit('u
.BI "bool __test_and_clear_bit(long\ " "nr" ", volatile\ unsigned\ long\ *\ " "addr" ");"
.SH "ARGUMENTS"
.PP
\fInr\fR
.RS 4
Bit to clear
.RE
.PP
\fIaddr\fR
.RS 4
Address to count from
.RE
.SH "DESCRIPTION"
.PP
This operation is non\-atomic and can be reordered\&. If two examples of this operation race, one can appear to succeed but actually fail\&. You must protect multiple accesses with a lock\&.
.SH "NOTE"
.PP
the operation is performed atomically with respect to the local CPU, but not other CPUs\&. Portable code should not rely on this behaviour\&. KVM relies on this behaviour on x86 for modifying memory that is also accessed from a hypervisor on the same CPU if running in a VM: don\*(Aqt change this without also updating arch/x86/kernel/kvm\&.c
.SH "COPYRIGHT"
.br