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del_timer_sync(9) [centos man page]

DEL_TIMER_SYNC(9)						   Driver Basics						 DEL_TIMER_SYNC(9)

NAME
del_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. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 DEL_TIMER_SYNC(9)

Check Out this Related Man Page

mktimer(3C)															       mktimer(3C)

NAME
mktimer - allocate a per-process timer SYNOPSIS
DESCRIPTION
The function is used to allocate a per-process timer using the specified system-wide clock as the timing base. returns an unique timer ID of type used to identify the timer in timer requests (see gettimer(3C)). specifies the system-wide clock to be used as the timing base for the new timer. specifies the mechanism by which the process is to be notified when the timer expires. supports one per-process timer with a of and of If is the system causes a signal to be sent to the process whenever the timer expires. For the machine-dependent clock resolution and maximum value are and seconds, respectively. These constants are defined in RETURN VALUE
Upon successful completion, returns a which can be passed to the per_process timer calls. If unsuccessful, returns a value of and sets to indicate the error. ERRORS
fails if any of the following conditions are encountered: [EAGAIN] The calling process has already allocated all of the timers it is allowed. [EINVAL] is not defined, or does not allow the specified notification mechanism. FILES
SEE ALSO timers(2), getclock(3C), gettimer(3C), reltimer(3C), rmtimer(3C), setclock(3C), thread_safety(5). STANDARDS CONFORMANCE
mktimer(3C)

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