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.\"     Title: rcu_read_lock_sched_held
.\"    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 "RCU_READ_LOCK_SCHED_" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Driver Basics"
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.SH "NAME"
rcu_read_lock_sched_held \- might we be in RCU\-sched read\-side critical section?
.SH "SYNOPSIS"
.HP \w'int\ rcu_read_lock_sched_held('u
.BI "int rcu_read_lock_sched_held(" "void" ");"
.SH "ARGUMENTS"
.PP
\fIvoid\fR
.RS 4
no arguments
.RE
.SH "DESCRIPTION"
.PP
.PP
If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU\-sched read\-side critical section\&. In absence of CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU\-sched read\-side critical section unless it can prove otherwise\&. Note that disabling of preemption (including disabling irqs) counts as an RCU\-sched read\-side critical section\&. This is useful for debug checks in functions that required that they be called within an RCU\-sched read\-side critical section\&.
.PP
Check
\fBdebug_lockdep_rcu_enabled\fR
to prevent false positives during boot and while lockdep is disabled\&.
.PP
Note that if the CPU is in the idle loop from an RCU point of view (ie: that we are in the section between
\fBrcu_idle_enter\fR
and
\fBrcu_idle_exit\fR) then
\fBrcu_read_lock_held\fR
returns false even if the CPU did an
\fBrcu_read_lock\fR\&. The reason for this is that RCU ignores CPUs that are in such a section, considering these as in extended quiescent state, so such a CPU is effectively never in an RCU read\-side critical section regardless of what RCU primitives it invokes\&. This state of affairs is required \-\-\- we need to keep an RCU\-free window in idle where the CPU may possibly enter into low power mode\&. This way we can notice an extended quiescent state to other CPUs that started a grace period\&. Otherwise we would delay any grace period as long as we run in the idle task\&.
.PP
Similarly, we avoid claiming an SRCU read lock held if the current CPU is offline\&.
.SH "COPYRIGHT"
.br