DEL_TIMER_SYNC(9) Driver Basics DEL_TIMER_SYNC(9)NAMEdel_timer_sync - deactivate a timer and wait for the handler to finish.
SYNOPSIS
int del_timer_sync(struct timer_list * timer);
ARGUMENTS
timer
the timer to be deactivated
DESCRIPTION
This function only differs from del_timer on SMP: besides deactivating
the timer it also makes sure the handler has finished executing on
other CPUs.
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's handler. The timer's handler must not
call add_timer_on. Upon exit the timer is not queued and the handler is
not running on any CPU.
NOTE
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's why:
CPU0 CPU1 ---- ---- <SOFTIRQ> call_timer_fn; base->running_timer =
mytimer; spin_lock_irq(somelock); <IRQ> spin_lock(somelock);
del_timer_sync(mytimer); while (base->running_timer == mytimer);
Now del_timer_sync 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.
The function returns whether it has deactivated a pending timer or not.
COPYRIGHTKernel Hackers Manual 3.11 November 2013 DEL_TIMER_SYNC(9)