'\" t
.\"     Title: del_timer_sync
.\"    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 "DEL_TIMER_SYNC" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Driver Basics"
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.SH "NAME"
del_timer_sync \- deactivate a timer and wait for the handler to finish\&.
.SH "SYNOPSIS"
.HP \w'int\ del_timer_sync('u
.BI "int del_timer_sync(struct\ timer_list\ *\ " "timer" ");"
.SH "ARGUMENTS"
.PP
\fItimer\fR
.RS 4
the timer to be deactivated
.RE
.SH "DESCRIPTION"
.PP
This function only differs from
\fBdel_timer\fR
on SMP: besides deactivating the timer it also makes sure the handler has finished executing on other CPUs\&.
.PP
Synchronization rules: Callers must prevent restarting of the timer, otherwise this function is meaningless\&. It must not be called from interrupt contexts unless the timer is an irqsafe one\&. The caller must not hold locks which would prevent completion of the timer\*(Aqs handler\&. The timer\*(Aqs handler must not call
\fBadd_timer_on\fR\&. Upon exit the timer is not queued and the handler is not running on any CPU\&.
.SH "NOTE"
.PP
For !irqsafe timers, you must not hold locks that are held in interrupt context while calling this function\&. Even if the lock has nothing to do with the timer in question\&. Here\*(Aqs why:
.PP
CPU0 CPU1 \-\-\-\- \-\-\-\- <SOFTIRQ>
\fBcall_timer_fn\fR; base\->running_timer = mytimer; spin_lock_irq(somelock); <IRQ> spin_lock(somelock); del_timer_sync(mytimer); while (base\->running_timer == mytimer);
.PP
Now
\fBdel_timer_sync\fR
will never return and never release somelock\&. The interrupt on the other CPU is waiting to grab somelock but it has interrupted the softirq that CPU0 is waiting to finish\&.
.PP
The function returns whether it has deactivated a pending timer or not\&.
.SH "COPYRIGHT"
.br