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.\"     Title: synchronize_rcu_tasks
.\"    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: Driver Basics
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "SYNCHRONIZE_RCU_TASK" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Driver Basics"
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.SH "NAME"
synchronize_rcu_tasks \- wait until an rcu\-tasks grace period has elapsed\&.
.SH "SYNOPSIS"
.HP \w'void\ synchronize_rcu_tasks('u
.BI "void synchronize_rcu_tasks(" "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\-tasks grace period has elapsed, in other words after all currently executing rcu\-tasks read\-side critical sections have elapsed\&. These read\-side critical sections are delimited by calls to
\fBschedule\fR,
\fBcond_resched_rcu_qs\fR, idle execution, userspace execution, calls to
\fBsynchronize_rcu_tasks\fR, and (in theory, anyway)
\fBcond_resched\fR\&.
.PP
This is a very specialized primitive, intended only for a few uses in tracing and other situations requiring manipulation of function preambles and profiling hooks\&. The
\fBsynchronize_rcu_tasks\fR
function is not (yet) intended for heavy use from multiple CPUs\&.
.PP
Note that this guarantee implies further memory\-ordering guarantees\&. On systems with more than one CPU, when
\fBsynchronize_rcu_tasks\fR
returns, each CPU is guaranteed to have executed a full memory barrier since the end of its last RCU\-tasks read\-side critical section whose beginning preceded the call to
\fBsynchronize_rcu_tasks\fR\&. In addition, each CPU having an RCU\-tasks read\-side critical section that extends beyond the return from
\fBsynchronize_rcu_tasks\fR
is guaranteed to have executed a full memory barrier after the beginning of
\fBsynchronize_rcu_tasks\fR
and before the beginning of that RCU\-tasks 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_rcu_tasks\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_rcu_tasks\fR
\-\- even if CPU A and CPU B are the same CPU (but again only if the system has more than one CPU)\&.
.SH "COPYRIGHT"
.br