'\" t
.\"     Title: synchronize_sched
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Driver Basics
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "SYNCHRONIZE_SCHED" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Driver Basics"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
synchronize_sched \- wait until an rcu\-sched grace period has elapsed\&.
.SH "SYNOPSIS"
.HP \w'void\ synchronize_sched('u
.BI "void synchronize_sched(" "void" ");"
.SH "ARGUMENTS"
.PP
\fIvoid\fR
.RS 4
no arguments
.RE
.SH "DESCRIPTION"
.PP
.PP
Control will return to the caller some time after a full rcu\-sched grace period has elapsed, in other words after all currently executing rcu\-sched read\-side critical sections have completed\&. These read\-side critical sections are delimited by
\fBrcu_read_lock_sched\fR
and
\fBrcu_read_unlock_sched\fR, and may be nested\&. Note that
\fBpreempt_disable\fR,
\fBlocal_irq_disable\fR, and so on may be used in place of
\fBrcu_read_lock_sched\fR\&.
.PP
This means that all preempt_disable code sequences, including NMI and non\-threaded hardware\-interrupt handlers, in progress on entry will have completed before this primitive returns\&. However, this does not guarantee that softirq handlers will have completed, since in some kernels, these handlers can run in process context, and can block\&.
.PP
Note that this guarantee implies further memory\-ordering guarantees\&. On systems with more than one CPU, when
\fBsynchronize_sched\fR
returns, each CPU is guaranteed to have executed a full memory barrier since the end of its last RCU\-sched read\-side critical section whose beginning preceded the call to
\fBsynchronize_sched\fR\&. In addition, each CPU having an RCU read\-side critical section that extends beyond the return from
\fBsynchronize_sched\fR
is guaranteed to have executed a full memory barrier after the beginning of
\fBsynchronize_sched\fR
and before the beginning of that RCU read\-side critical section\&. Note that these guarantees include CPUs that are offline, idle, or executing in user mode, as well as CPUs that are executing in the kernel\&.
.PP
Furthermore, if CPU A invoked
\fBsynchronize_sched\fR, which returned to its caller on CPU B, then both CPU A and CPU B are guaranteed to have executed a full memory barrier during the execution of
\fBsynchronize_sched\fR
\-\- even if CPU A and CPU B are the same CPU (but again only if the system has more than one CPU)\&.
.PP
This primitive provides the guarantees made by the (now removed)
\fBsynchronize_kernel\fR
API\&. In contrast,
\fBsynchronize_rcu\fR
only guarantees that
\fBrcu_read_lock\fR
sections will have completed\&. In
\(lqclassic RCU\(rq, these two guarantees happen to be one and the same, but can differ in realtime RCU implementations\&.
.SH "COPYRIGHT"
.br