2 * linux/kernel/softirq.c
4 * Copyright (C) 1992 Linus Torvalds
6 * Distribute under GPLv2.
8 * Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
10 * Remote softirq infrastructure is by Jens Axboe.
13 #include <linux/export.h>
14 #include <linux/kernel_stat.h>
15 #include <linux/interrupt.h>
16 #include <linux/init.h>
18 #include <linux/notifier.h>
19 #include <linux/percpu.h>
20 #include <linux/cpu.h>
21 #include <linux/freezer.h>
22 #include <linux/kthread.h>
23 #include <linux/rcupdate.h>
24 #include <linux/ftrace.h>
25 #include <linux/smp.h>
26 #include <linux/tick.h>
28 #define CREATE_TRACE_POINTS
29 #include <trace/events/irq.h>
33 - No shared variables, all the data are CPU local.
34 - If a softirq needs serialization, let it serialize itself
36 - Even if softirq is serialized, only local cpu is marked for
37 execution. Hence, we get something sort of weak cpu binding.
38 Though it is still not clear, will it result in better locality
42 - NET RX softirq. It is multithreaded and does not require
43 any global serialization.
44 - NET TX softirq. It kicks software netdevice queues, hence
45 it is logically serialized per device, but this serialization
46 is invisible to common code.
47 - Tasklets: serialized wrt itself.
50 #ifndef __ARCH_IRQ_STAT
51 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
52 EXPORT_SYMBOL(irq_stat);
55 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
57 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
59 char *softirq_to_name[NR_SOFTIRQS] = {
60 "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
61 "TASKLET", "SCHED", "HRTIMER", "RCU"
65 * we cannot loop indefinitely here to avoid userspace starvation,
66 * but we also don't want to introduce a worst case 1/HZ latency
67 * to the pending events, so lets the scheduler to balance
68 * the softirq load for us.
70 static void wakeup_softirqd(void)
72 /* Interrupts are disabled: no need to stop preemption */
73 struct task_struct *tsk = __this_cpu_read(ksoftirqd);
75 if (tsk && tsk->state != TASK_RUNNING)
80 * preempt_count and SOFTIRQ_OFFSET usage:
81 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
83 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
84 * on local_bh_disable or local_bh_enable.
85 * This lets us distinguish between whether we are currently processing
86 * softirq and whether we just have bh disabled.
90 * This one is for softirq.c-internal use,
91 * where hardirqs are disabled legitimately:
93 #ifdef CONFIG_TRACE_IRQFLAGS
94 static void __local_bh_disable(unsigned long ip, unsigned int cnt)
98 WARN_ON_ONCE(in_irq());
100 raw_local_irq_save(flags);
102 * The preempt tracer hooks into add_preempt_count and will break
103 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
104 * is set and before current->softirq_enabled is cleared.
105 * We must manually increment preempt_count here and manually
106 * call the trace_preempt_off later.
108 preempt_count() += cnt;
110 * Were softirqs turned off above:
112 if (softirq_count() == cnt)
113 trace_softirqs_off(ip);
114 raw_local_irq_restore(flags);
116 if (preempt_count() == cnt)
117 trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
119 #else /* !CONFIG_TRACE_IRQFLAGS */
120 static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
122 add_preempt_count(cnt);
125 #endif /* CONFIG_TRACE_IRQFLAGS */
127 void local_bh_disable(void)
129 __local_bh_disable((unsigned long)__builtin_return_address(0),
130 SOFTIRQ_DISABLE_OFFSET);
133 EXPORT_SYMBOL(local_bh_disable);
135 static void __local_bh_enable(unsigned int cnt)
137 WARN_ON_ONCE(in_irq());
138 WARN_ON_ONCE(!irqs_disabled());
140 if (softirq_count() == cnt)
141 trace_softirqs_on((unsigned long)__builtin_return_address(0));
142 sub_preempt_count(cnt);
146 * Special-case - softirqs can safely be enabled in
147 * cond_resched_softirq(), or by __do_softirq(),
148 * without processing still-pending softirqs:
150 void _local_bh_enable(void)
152 __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
155 EXPORT_SYMBOL(_local_bh_enable);
157 static inline void _local_bh_enable_ip(unsigned long ip)
159 WARN_ON_ONCE(in_irq() || irqs_disabled());
160 #ifdef CONFIG_TRACE_IRQFLAGS
164 * Are softirqs going to be turned on now:
166 if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
167 trace_softirqs_on(ip);
169 * Keep preemption disabled until we are done with
170 * softirq processing:
172 sub_preempt_count(SOFTIRQ_DISABLE_OFFSET - 1);
174 if (unlikely(!in_interrupt() && local_softirq_pending()))
178 #ifdef CONFIG_TRACE_IRQFLAGS
181 preempt_check_resched();
184 void local_bh_enable(void)
186 _local_bh_enable_ip((unsigned long)__builtin_return_address(0));
188 EXPORT_SYMBOL(local_bh_enable);
190 void local_bh_enable_ip(unsigned long ip)
192 _local_bh_enable_ip(ip);
194 EXPORT_SYMBOL(local_bh_enable_ip);
197 * We restart softirq processing MAX_SOFTIRQ_RESTART times,
198 * and we fall back to softirqd after that.
200 * This number has been established via experimentation.
201 * The two things to balance is latency against fairness -
202 * we want to handle softirqs as soon as possible, but they
203 * should not be able to lock up the box.
205 #define MAX_SOFTIRQ_RESTART 10
207 asmlinkage void __do_softirq(void)
209 struct softirq_action *h;
211 int max_restart = MAX_SOFTIRQ_RESTART;
214 pending = local_softirq_pending();
215 account_system_vtime(current);
217 __local_bh_disable((unsigned long)__builtin_return_address(0),
219 lockdep_softirq_enter();
221 cpu = smp_processor_id();
223 /* Reset the pending bitmask before enabling irqs */
224 set_softirq_pending(0);
232 unsigned int vec_nr = h - softirq_vec;
233 int prev_count = preempt_count();
235 kstat_incr_softirqs_this_cpu(vec_nr);
237 trace_softirq_entry(vec_nr);
239 trace_softirq_exit(vec_nr);
240 if (unlikely(prev_count != preempt_count())) {
241 printk(KERN_ERR "huh, entered softirq %u %s %p"
242 "with preempt_count %08x,"
243 " exited with %08x?\n", vec_nr,
244 softirq_to_name[vec_nr], h->action,
245 prev_count, preempt_count());
246 preempt_count() = prev_count;
257 pending = local_softirq_pending();
258 if (pending && --max_restart)
264 lockdep_softirq_exit();
266 account_system_vtime(current);
267 __local_bh_enable(SOFTIRQ_OFFSET);
270 #ifndef __ARCH_HAS_DO_SOFTIRQ
272 asmlinkage void do_softirq(void)
280 local_irq_save(flags);
282 pending = local_softirq_pending();
287 local_irq_restore(flags);
293 * Enter an interrupt context.
297 int cpu = smp_processor_id();
300 if (idle_cpu(cpu) && !in_interrupt()) {
302 * Prevent raise_softirq from needlessly waking up ksoftirqd
303 * here, as softirq will be serviced on return from interrupt.
306 tick_check_idle(cpu);
313 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
314 static inline void invoke_softirq(void)
316 if (!force_irqthreads)
319 __local_bh_disable((unsigned long)__builtin_return_address(0),
322 __local_bh_enable(SOFTIRQ_OFFSET);
326 static inline void invoke_softirq(void)
328 if (!force_irqthreads)
331 __local_bh_disable((unsigned long)__builtin_return_address(0),
334 __local_bh_enable(SOFTIRQ_OFFSET);
340 * Exit an interrupt context. Process softirqs if needed and possible:
344 account_system_vtime(current);
345 trace_hardirq_exit();
346 sub_preempt_count(IRQ_EXIT_OFFSET);
347 if (!in_interrupt() && local_softirq_pending())
352 /* Make sure that timer wheel updates are propagated */
353 if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched())
354 tick_nohz_stop_sched_tick(0);
356 preempt_enable_no_resched();
360 * This function must run with irqs disabled!
362 inline void raise_softirq_irqoff(unsigned int nr)
364 __raise_softirq_irqoff(nr);
367 * If we're in an interrupt or softirq, we're done
368 * (this also catches softirq-disabled code). We will
369 * actually run the softirq once we return from
370 * the irq or softirq.
372 * Otherwise we wake up ksoftirqd to make sure we
373 * schedule the softirq soon.
379 void raise_softirq(unsigned int nr)
383 local_irq_save(flags);
384 raise_softirq_irqoff(nr);
385 local_irq_restore(flags);
388 void open_softirq(int nr, void (*action)(struct softirq_action *))
390 softirq_vec[nr].action = action;
398 struct tasklet_struct *head;
399 struct tasklet_struct **tail;
402 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
403 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
405 void __tasklet_schedule(struct tasklet_struct *t)
409 local_irq_save(flags);
411 *__this_cpu_read(tasklet_vec.tail) = t;
412 __this_cpu_write(tasklet_vec.tail, &(t->next));
413 raise_softirq_irqoff(TASKLET_SOFTIRQ);
414 local_irq_restore(flags);
417 EXPORT_SYMBOL(__tasklet_schedule);
419 void __tasklet_hi_schedule(struct tasklet_struct *t)
423 local_irq_save(flags);
425 *__this_cpu_read(tasklet_hi_vec.tail) = t;
426 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
427 raise_softirq_irqoff(HI_SOFTIRQ);
428 local_irq_restore(flags);
431 EXPORT_SYMBOL(__tasklet_hi_schedule);
433 void __tasklet_hi_schedule_first(struct tasklet_struct *t)
435 BUG_ON(!irqs_disabled());
437 t->next = __this_cpu_read(tasklet_hi_vec.head);
438 __this_cpu_write(tasklet_hi_vec.head, t);
439 __raise_softirq_irqoff(HI_SOFTIRQ);
442 EXPORT_SYMBOL(__tasklet_hi_schedule_first);
444 static void tasklet_action(struct softirq_action *a)
446 struct tasklet_struct *list;
449 list = __this_cpu_read(tasklet_vec.head);
450 __this_cpu_write(tasklet_vec.head, NULL);
451 __this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head);
455 struct tasklet_struct *t = list;
459 if (tasklet_trylock(t)) {
460 if (!atomic_read(&t->count)) {
461 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
472 *__this_cpu_read(tasklet_vec.tail) = t;
473 __this_cpu_write(tasklet_vec.tail, &(t->next));
474 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
479 static void tasklet_hi_action(struct softirq_action *a)
481 struct tasklet_struct *list;
484 list = __this_cpu_read(tasklet_hi_vec.head);
485 __this_cpu_write(tasklet_hi_vec.head, NULL);
486 __this_cpu_write(tasklet_hi_vec.tail, &__get_cpu_var(tasklet_hi_vec).head);
490 struct tasklet_struct *t = list;
494 if (tasklet_trylock(t)) {
495 if (!atomic_read(&t->count)) {
496 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
507 *__this_cpu_read(tasklet_hi_vec.tail) = t;
508 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
509 __raise_softirq_irqoff(HI_SOFTIRQ);
515 void tasklet_init(struct tasklet_struct *t,
516 void (*func)(unsigned long), unsigned long data)
520 atomic_set(&t->count, 0);
525 EXPORT_SYMBOL(tasklet_init);
527 void tasklet_kill(struct tasklet_struct *t)
530 printk("Attempt to kill tasklet from interrupt\n");
532 while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
535 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
537 tasklet_unlock_wait(t);
538 clear_bit(TASKLET_STATE_SCHED, &t->state);
541 EXPORT_SYMBOL(tasklet_kill);
548 * The trampoline is called when the hrtimer expires. It schedules a tasklet
549 * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
550 * hrtimer callback, but from softirq context.
552 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
554 struct tasklet_hrtimer *ttimer =
555 container_of(timer, struct tasklet_hrtimer, timer);
557 tasklet_hi_schedule(&ttimer->tasklet);
558 return HRTIMER_NORESTART;
562 * Helper function which calls the hrtimer callback from
563 * tasklet/softirq context
565 static void __tasklet_hrtimer_trampoline(unsigned long data)
567 struct tasklet_hrtimer *ttimer = (void *)data;
568 enum hrtimer_restart restart;
570 restart = ttimer->function(&ttimer->timer);
571 if (restart != HRTIMER_NORESTART)
572 hrtimer_restart(&ttimer->timer);
576 * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
577 * @ttimer: tasklet_hrtimer which is initialized
578 * @function: hrtimer callback function which gets called from softirq context
579 * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
580 * @mode: hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
582 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
583 enum hrtimer_restart (*function)(struct hrtimer *),
584 clockid_t which_clock, enum hrtimer_mode mode)
586 hrtimer_init(&ttimer->timer, which_clock, mode);
587 ttimer->timer.function = __hrtimer_tasklet_trampoline;
588 tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
589 (unsigned long)ttimer);
590 ttimer->function = function;
592 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
595 * Remote softirq bits
598 DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
599 EXPORT_PER_CPU_SYMBOL(softirq_work_list);
601 static void __local_trigger(struct call_single_data *cp, int softirq)
603 struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
605 list_add_tail(&cp->list, head);
607 /* Trigger the softirq only if the list was previously empty. */
608 if (head->next == &cp->list)
609 raise_softirq_irqoff(softirq);
612 #ifdef CONFIG_USE_GENERIC_SMP_HELPERS
613 static void remote_softirq_receive(void *data)
615 struct call_single_data *cp = data;
621 local_irq_save(flags);
622 __local_trigger(cp, softirq);
623 local_irq_restore(flags);
626 static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
628 if (cpu_online(cpu)) {
629 cp->func = remote_softirq_receive;
634 __smp_call_function_single(cpu, cp, 0);
639 #else /* CONFIG_USE_GENERIC_SMP_HELPERS */
640 static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
647 * __send_remote_softirq - try to schedule softirq work on a remote cpu
648 * @cp: private SMP call function data area
649 * @cpu: the remote cpu
650 * @this_cpu: the currently executing cpu
651 * @softirq: the softirq for the work
653 * Attempt to schedule softirq work on a remote cpu. If this cannot be
654 * done, the work is instead queued up on the local cpu.
656 * Interrupts must be disabled.
658 void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
660 if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
661 __local_trigger(cp, softirq);
663 EXPORT_SYMBOL(__send_remote_softirq);
666 * send_remote_softirq - try to schedule softirq work on a remote cpu
667 * @cp: private SMP call function data area
668 * @cpu: the remote cpu
669 * @softirq: the softirq for the work
671 * Like __send_remote_softirq except that disabling interrupts and
672 * computing the current cpu is done for the caller.
674 void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
679 local_irq_save(flags);
680 this_cpu = smp_processor_id();
681 __send_remote_softirq(cp, cpu, this_cpu, softirq);
682 local_irq_restore(flags);
684 EXPORT_SYMBOL(send_remote_softirq);
686 static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
687 unsigned long action, void *hcpu)
690 * If a CPU goes away, splice its entries to the current CPU
691 * and trigger a run of the softirq
693 if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
694 int cpu = (unsigned long) hcpu;
698 for (i = 0; i < NR_SOFTIRQS; i++) {
699 struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
700 struct list_head *local_head;
702 if (list_empty(head))
705 local_head = &__get_cpu_var(softirq_work_list[i]);
706 list_splice_init(head, local_head);
707 raise_softirq_irqoff(i);
715 static struct notifier_block __cpuinitdata remote_softirq_cpu_notifier = {
716 .notifier_call = remote_softirq_cpu_notify,
719 void __init softirq_init(void)
723 for_each_possible_cpu(cpu) {
726 per_cpu(tasklet_vec, cpu).tail =
727 &per_cpu(tasklet_vec, cpu).head;
728 per_cpu(tasklet_hi_vec, cpu).tail =
729 &per_cpu(tasklet_hi_vec, cpu).head;
730 for (i = 0; i < NR_SOFTIRQS; i++)
731 INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
734 register_hotcpu_notifier(&remote_softirq_cpu_notifier);
736 open_softirq(TASKLET_SOFTIRQ, tasklet_action);
737 open_softirq(HI_SOFTIRQ, tasklet_hi_action);
740 static int run_ksoftirqd(void * __bind_cpu)
742 set_current_state(TASK_INTERRUPTIBLE);
744 while (!kthread_should_stop()) {
746 if (!local_softirq_pending()) {
747 preempt_enable_no_resched();
752 __set_current_state(TASK_RUNNING);
754 while (local_softirq_pending()) {
755 /* Preempt disable stops cpu going offline.
756 If already offline, we'll be on wrong CPU:
758 if (cpu_is_offline((long)__bind_cpu))
761 if (local_softirq_pending())
764 preempt_enable_no_resched();
767 rcu_note_context_switch((long)__bind_cpu);
770 set_current_state(TASK_INTERRUPTIBLE);
772 __set_current_state(TASK_RUNNING);
777 /* Wait for kthread_stop */
778 set_current_state(TASK_INTERRUPTIBLE);
779 while (!kthread_should_stop()) {
781 set_current_state(TASK_INTERRUPTIBLE);
783 __set_current_state(TASK_RUNNING);
787 #ifdef CONFIG_HOTPLUG_CPU
789 * tasklet_kill_immediate is called to remove a tasklet which can already be
790 * scheduled for execution on @cpu.
792 * Unlike tasklet_kill, this function removes the tasklet
793 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
795 * When this function is called, @cpu must be in the CPU_DEAD state.
797 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
799 struct tasklet_struct **i;
801 BUG_ON(cpu_online(cpu));
802 BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
804 if (!test_bit(TASKLET_STATE_SCHED, &t->state))
807 /* CPU is dead, so no lock needed. */
808 for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
811 /* If this was the tail element, move the tail ptr */
813 per_cpu(tasklet_vec, cpu).tail = i;
820 static void takeover_tasklets(unsigned int cpu)
822 /* CPU is dead, so no lock needed. */
825 /* Find end, append list for that CPU. */
826 if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
827 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
828 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
829 per_cpu(tasklet_vec, cpu).head = NULL;
830 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
832 raise_softirq_irqoff(TASKLET_SOFTIRQ);
834 if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
835 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
836 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
837 per_cpu(tasklet_hi_vec, cpu).head = NULL;
838 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
840 raise_softirq_irqoff(HI_SOFTIRQ);
844 #endif /* CONFIG_HOTPLUG_CPU */
846 static int __cpuinit cpu_callback(struct notifier_block *nfb,
847 unsigned long action,
850 int hotcpu = (unsigned long)hcpu;
851 struct task_struct *p;
855 case CPU_UP_PREPARE_FROZEN:
856 p = kthread_create_on_node(run_ksoftirqd,
859 "ksoftirqd/%d", hotcpu);
861 printk("ksoftirqd for %i failed\n", hotcpu);
862 return notifier_from_errno(PTR_ERR(p));
864 kthread_bind(p, hotcpu);
865 per_cpu(ksoftirqd, hotcpu) = p;
868 case CPU_ONLINE_FROZEN:
869 wake_up_process(per_cpu(ksoftirqd, hotcpu));
871 #ifdef CONFIG_HOTPLUG_CPU
872 case CPU_UP_CANCELED:
873 case CPU_UP_CANCELED_FROZEN:
874 if (!per_cpu(ksoftirqd, hotcpu))
876 /* Unbind so it can run. Fall thru. */
877 kthread_bind(per_cpu(ksoftirqd, hotcpu),
878 cpumask_any(cpu_online_mask));
880 case CPU_DEAD_FROZEN: {
881 static const struct sched_param param = {
882 .sched_priority = MAX_RT_PRIO-1
885 p = per_cpu(ksoftirqd, hotcpu);
886 per_cpu(ksoftirqd, hotcpu) = NULL;
887 sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m);
889 takeover_tasklets(hotcpu);
892 #endif /* CONFIG_HOTPLUG_CPU */
897 static struct notifier_block __cpuinitdata cpu_nfb = {
898 .notifier_call = cpu_callback
901 static __init int spawn_ksoftirqd(void)
903 void *cpu = (void *)(long)smp_processor_id();
904 int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
906 BUG_ON(err != NOTIFY_OK);
907 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
908 register_cpu_notifier(&cpu_nfb);
911 early_initcall(spawn_ksoftirqd);
914 * [ These __weak aliases are kept in a separate compilation unit, so that
915 * GCC does not inline them incorrectly. ]
918 int __init __weak early_irq_init(void)
923 #ifdef CONFIG_GENERIC_HARDIRQS
924 int __init __weak arch_probe_nr_irqs(void)
926 return NR_IRQS_LEGACY;
929 int __init __weak arch_early_irq_init(void)