spin_lock---------------------spin_unlock------------------最轻
spin_lock_bh----------------spin_unlock_bh-----------------较轻
spin_lock_irq----------------spin_unlock_irq---------------较重
spin_lock_irqsave---------spin_lock_irqrestore--------------最重

static inline int
__mod_timer(struct timer_list *timer, unsigned long expires,bool pending_only, int pinned)
{struct tvec_base *base, *new_base;unsigned long flags;int ret = 0 , cpu;timer_stats_timer_set_start_info(timer);BUG_ON(!timer->function);base = lock_timer_base(timer, &flags);ret = detach_if_pending(timer, base, false);if (!ret && pending_only)goto out_unlock;debug_activate(timer, expires);cpu = smp_processor_id();#if defined(CONFIG_NO_HZ_COMMON) && defined(CONFIG_SMP)if (!pinned && get_sysctl_timer_migration())cpu = get_nohz_timer_target();
#endifnew_base = per_cpu(tvec_bases, cpu);if (base != new_base) {/** We are trying to schedule the timer on the local CPU.* However we can't change timer's base while it is running,* otherwise del_timer_sync() can't detect that the timer's* handler yet has not finished. This also guarantees that* the timer is serialized wrt itself.*/if (likely(base->running_timer != timer)) {/* See the comment in lock_timer_base() */timer_set_base(timer, NULL);spin_unlock(&base->lock);base = new_base;spin_lock(&base->lock);timer_set_base(timer, base);}}timer->expires = expires;internal_add_timer(base, timer);out_unlock:spin_unlock_irqrestore(&base->lock, flags);-----------收尾很重要return ret;
}