1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/kernel/softirq.c
5 * Copyright (C) 1992 Linus Torvalds
7 * Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12 #include <linux/export.h>
13 #include <linux/kernel_stat.h>
14 #include <linux/interrupt.h>
15 #include <linux/init.h>
17 #include <linux/notifier.h>
18 #include <linux/percpu.h>
19 #include <linux/cpu.h>
20 #include <linux/freezer.h>
21 #include <linux/kthread.h>
22 #include <linux/rcupdate.h>
23 #include <linux/ftrace.h>
24 #include <linux/smp.h>
25 #include <linux/smpboot.h>
26 #include <linux/tick.h>
27 #include <linux/irq.h>
29 #define CREATE_TRACE_POINTS
30 #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 DEFINE_PER_CPU_ALIGNED(irq_cpustat_t
, irq_stat
);
52 EXPORT_PER_CPU_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 const char * const softirq_to_name
[NR_SOFTIRQS
] = {
60 "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
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 * If ksoftirqd is scheduled, we do not want to process pending softirqs
81 * right now. Let ksoftirqd handle this at its own rate, to get fairness,
82 * unless we're doing some of the synchronous softirqs.
84 #define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
85 static bool ksoftirqd_running(unsigned long pending
)
87 struct task_struct
*tsk
= __this_cpu_read(ksoftirqd
);
89 if (pending
& SOFTIRQ_NOW_MASK
)
91 return tsk
&& (tsk
->state
== TASK_RUNNING
) &&
92 !__kthread_should_park(tsk
);
96 * preempt_count and SOFTIRQ_OFFSET usage:
97 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
99 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
100 * on local_bh_disable or local_bh_enable.
101 * This lets us distinguish between whether we are currently processing
102 * softirq and whether we just have bh disabled.
106 * This one is for softirq.c-internal use,
107 * where hardirqs are disabled legitimately:
109 #ifdef CONFIG_TRACE_IRQFLAGS
110 void __local_bh_disable_ip(unsigned long ip
, unsigned int cnt
)
114 WARN_ON_ONCE(in_irq());
116 raw_local_irq_save(flags
);
118 * The preempt tracer hooks into preempt_count_add and will break
119 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
120 * is set and before current->softirq_enabled is cleared.
121 * We must manually increment preempt_count here and manually
122 * call the trace_preempt_off later.
124 __preempt_count_add(cnt
);
126 * Were softirqs turned off above:
128 if (softirq_count() == (cnt
& SOFTIRQ_MASK
))
129 lockdep_softirqs_off(ip
);
130 raw_local_irq_restore(flags
);
132 if (preempt_count() == cnt
) {
133 #ifdef CONFIG_DEBUG_PREEMPT
134 current
->preempt_disable_ip
= get_lock_parent_ip();
136 trace_preempt_off(CALLER_ADDR0
, get_lock_parent_ip());
139 EXPORT_SYMBOL(__local_bh_disable_ip
);
140 #endif /* CONFIG_TRACE_IRQFLAGS */
142 static void __local_bh_enable(unsigned int cnt
)
144 lockdep_assert_irqs_disabled();
146 if (preempt_count() == cnt
)
147 trace_preempt_on(CALLER_ADDR0
, get_lock_parent_ip());
149 if (softirq_count() == (cnt
& SOFTIRQ_MASK
))
150 lockdep_softirqs_on(_RET_IP_
);
152 __preempt_count_sub(cnt
);
156 * Special-case - softirqs can safely be enabled by __do_softirq(),
157 * without processing still-pending softirqs:
159 void _local_bh_enable(void)
161 WARN_ON_ONCE(in_irq());
162 __local_bh_enable(SOFTIRQ_DISABLE_OFFSET
);
164 EXPORT_SYMBOL(_local_bh_enable
);
166 void __local_bh_enable_ip(unsigned long ip
, unsigned int cnt
)
168 WARN_ON_ONCE(in_irq());
169 lockdep_assert_irqs_enabled();
170 #ifdef CONFIG_TRACE_IRQFLAGS
174 * Are softirqs going to be turned on now:
176 if (softirq_count() == SOFTIRQ_DISABLE_OFFSET
)
177 lockdep_softirqs_on(ip
);
179 * Keep preemption disabled until we are done with
180 * softirq processing:
182 preempt_count_sub(cnt
- 1);
184 if (unlikely(!in_interrupt() && local_softirq_pending())) {
186 * Run softirq if any pending. And do it in its own stack
187 * as we may be calling this deep in a task call stack already.
193 #ifdef CONFIG_TRACE_IRQFLAGS
196 preempt_check_resched();
198 EXPORT_SYMBOL(__local_bh_enable_ip
);
201 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
202 * but break the loop if need_resched() is set or after 2 ms.
203 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
204 * certain cases, such as stop_machine(), jiffies may cease to
205 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
206 * well to make sure we eventually return from this method.
208 * These limits have been established via experimentation.
209 * The two things to balance is latency against fairness -
210 * we want to handle softirqs as soon as possible, but they
211 * should not be able to lock up the box.
213 #define MAX_SOFTIRQ_TIME msecs_to_jiffies(2)
214 #define MAX_SOFTIRQ_RESTART 10
216 #ifdef CONFIG_TRACE_IRQFLAGS
218 * When we run softirqs from irq_exit() and thus on the hardirq stack we need
219 * to keep the lockdep irq context tracking as tight as possible in order to
220 * not miss-qualify lock contexts and miss possible deadlocks.
223 static inline bool lockdep_softirq_start(void)
225 bool in_hardirq
= false;
227 if (lockdep_hardirq_context(current
)) {
229 lockdep_hardirq_exit();
232 lockdep_softirq_enter();
237 static inline void lockdep_softirq_end(bool in_hardirq
)
239 lockdep_softirq_exit();
242 lockdep_hardirq_enter();
245 static inline bool lockdep_softirq_start(void) { return false; }
246 static inline void lockdep_softirq_end(bool in_hardirq
) { }
249 asmlinkage __visible
void __softirq_entry
__do_softirq(void)
251 unsigned long end
= jiffies
+ MAX_SOFTIRQ_TIME
;
252 unsigned long old_flags
= current
->flags
;
253 int max_restart
= MAX_SOFTIRQ_RESTART
;
254 struct softirq_action
*h
;
260 * Mask out PF_MEMALLOC as the current task context is borrowed for the
261 * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
262 * again if the socket is related to swapping.
264 current
->flags
&= ~PF_MEMALLOC
;
266 pending
= local_softirq_pending();
267 account_irq_enter_time(current
);
269 __local_bh_disable_ip(_RET_IP_
, SOFTIRQ_OFFSET
);
270 in_hardirq
= lockdep_softirq_start();
273 /* Reset the pending bitmask before enabling irqs */
274 set_softirq_pending(0);
280 while ((softirq_bit
= ffs(pending
))) {
284 h
+= softirq_bit
- 1;
286 vec_nr
= h
- softirq_vec
;
287 prev_count
= preempt_count();
289 kstat_incr_softirqs_this_cpu(vec_nr
);
291 trace_softirq_entry(vec_nr
);
293 trace_softirq_exit(vec_nr
);
294 if (unlikely(prev_count
!= preempt_count())) {
295 pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
296 vec_nr
, softirq_to_name
[vec_nr
], h
->action
,
297 prev_count
, preempt_count());
298 preempt_count_set(prev_count
);
301 pending
>>= softirq_bit
;
304 if (__this_cpu_read(ksoftirqd
) == current
)
308 pending
= local_softirq_pending();
310 if (time_before(jiffies
, end
) && !need_resched() &&
317 lockdep_softirq_end(in_hardirq
);
318 account_irq_exit_time(current
);
319 __local_bh_enable(SOFTIRQ_OFFSET
);
320 WARN_ON_ONCE(in_interrupt());
321 current_restore_flags(old_flags
, PF_MEMALLOC
);
324 asmlinkage __visible
void do_softirq(void)
332 local_irq_save(flags
);
334 pending
= local_softirq_pending();
336 if (pending
&& !ksoftirqd_running(pending
))
337 do_softirq_own_stack();
339 local_irq_restore(flags
);
343 * irq_enter_rcu - Enter an interrupt context with RCU watching
345 void irq_enter_rcu(void)
347 if (is_idle_task(current
) && !in_interrupt()) {
349 * Prevent raise_softirq from needlessly waking up ksoftirqd
350 * here, as softirq will be serviced on return from interrupt.
360 * irq_enter - Enter an interrupt context including RCU update
368 static inline void invoke_softirq(void)
370 if (ksoftirqd_running(local_softirq_pending()))
373 if (!force_irqthreads
) {
374 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
376 * We can safely execute softirq on the current stack if
377 * it is the irq stack, because it should be near empty
383 * Otherwise, irq_exit() is called on the task stack that can
384 * be potentially deep already. So call softirq in its own stack
385 * to prevent from any overrun.
387 do_softirq_own_stack();
394 static inline void tick_irq_exit(void)
396 #ifdef CONFIG_NO_HZ_COMMON
397 int cpu
= smp_processor_id();
399 /* Make sure that timer wheel updates are propagated */
400 if ((idle_cpu(cpu
) && !need_resched()) || tick_nohz_full_cpu(cpu
)) {
402 tick_nohz_irq_exit();
407 static inline void __irq_exit_rcu(void)
409 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
412 lockdep_assert_irqs_disabled();
414 account_irq_exit_time(current
);
415 preempt_count_sub(HARDIRQ_OFFSET
);
416 if (!in_interrupt() && local_softirq_pending())
423 * irq_exit_rcu() - Exit an interrupt context without updating RCU
425 * Also processes softirqs if needed and possible.
427 void irq_exit_rcu(void)
431 lockdep_hardirq_exit();
435 * irq_exit - Exit an interrupt context, update RCU and lockdep
437 * Also processes softirqs if needed and possible.
444 lockdep_hardirq_exit();
448 * This function must run with irqs disabled!
450 inline void raise_softirq_irqoff(unsigned int nr
)
452 __raise_softirq_irqoff(nr
);
455 * If we're in an interrupt or softirq, we're done
456 * (this also catches softirq-disabled code). We will
457 * actually run the softirq once we return from
458 * the irq or softirq.
460 * Otherwise we wake up ksoftirqd to make sure we
461 * schedule the softirq soon.
467 void raise_softirq(unsigned int nr
)
471 local_irq_save(flags
);
472 raise_softirq_irqoff(nr
);
473 local_irq_restore(flags
);
476 void __raise_softirq_irqoff(unsigned int nr
)
478 trace_softirq_raise(nr
);
479 or_softirq_pending(1UL << nr
);
482 void open_softirq(int nr
, void (*action
)(struct softirq_action
*))
484 softirq_vec
[nr
].action
= action
;
490 struct tasklet_head
{
491 struct tasklet_struct
*head
;
492 struct tasklet_struct
**tail
;
495 static DEFINE_PER_CPU(struct tasklet_head
, tasklet_vec
);
496 static DEFINE_PER_CPU(struct tasklet_head
, tasklet_hi_vec
);
498 static void __tasklet_schedule_common(struct tasklet_struct
*t
,
499 struct tasklet_head __percpu
*headp
,
500 unsigned int softirq_nr
)
502 struct tasklet_head
*head
;
505 local_irq_save(flags
);
506 head
= this_cpu_ptr(headp
);
509 head
->tail
= &(t
->next
);
510 raise_softirq_irqoff(softirq_nr
);
511 local_irq_restore(flags
);
514 void __tasklet_schedule(struct tasklet_struct
*t
)
516 __tasklet_schedule_common(t
, &tasklet_vec
,
519 EXPORT_SYMBOL(__tasklet_schedule
);
521 void __tasklet_hi_schedule(struct tasklet_struct
*t
)
523 __tasklet_schedule_common(t
, &tasklet_hi_vec
,
526 EXPORT_SYMBOL(__tasklet_hi_schedule
);
528 static void tasklet_action_common(struct softirq_action
*a
,
529 struct tasklet_head
*tl_head
,
530 unsigned int softirq_nr
)
532 struct tasklet_struct
*list
;
535 list
= tl_head
->head
;
536 tl_head
->head
= NULL
;
537 tl_head
->tail
= &tl_head
->head
;
541 struct tasklet_struct
*t
= list
;
545 if (tasklet_trylock(t
)) {
546 if (!atomic_read(&t
->count
)) {
547 if (!test_and_clear_bit(TASKLET_STATE_SCHED
,
560 tl_head
->tail
= &t
->next
;
561 __raise_softirq_irqoff(softirq_nr
);
566 static __latent_entropy
void tasklet_action(struct softirq_action
*a
)
568 tasklet_action_common(a
, this_cpu_ptr(&tasklet_vec
), TASKLET_SOFTIRQ
);
571 static __latent_entropy
void tasklet_hi_action(struct softirq_action
*a
)
573 tasklet_action_common(a
, this_cpu_ptr(&tasklet_hi_vec
), HI_SOFTIRQ
);
576 void tasklet_init(struct tasklet_struct
*t
,
577 void (*func
)(unsigned long), unsigned long data
)
581 atomic_set(&t
->count
, 0);
585 EXPORT_SYMBOL(tasklet_init
);
587 void tasklet_kill(struct tasklet_struct
*t
)
590 pr_notice("Attempt to kill tasklet from interrupt\n");
592 while (test_and_set_bit(TASKLET_STATE_SCHED
, &t
->state
)) {
595 } while (test_bit(TASKLET_STATE_SCHED
, &t
->state
));
597 tasklet_unlock_wait(t
);
598 clear_bit(TASKLET_STATE_SCHED
, &t
->state
);
600 EXPORT_SYMBOL(tasklet_kill
);
602 void __init
softirq_init(void)
606 for_each_possible_cpu(cpu
) {
607 per_cpu(tasklet_vec
, cpu
).tail
=
608 &per_cpu(tasklet_vec
, cpu
).head
;
609 per_cpu(tasklet_hi_vec
, cpu
).tail
=
610 &per_cpu(tasklet_hi_vec
, cpu
).head
;
613 open_softirq(TASKLET_SOFTIRQ
, tasklet_action
);
614 open_softirq(HI_SOFTIRQ
, tasklet_hi_action
);
617 static int ksoftirqd_should_run(unsigned int cpu
)
619 return local_softirq_pending();
622 static void run_ksoftirqd(unsigned int cpu
)
625 if (local_softirq_pending()) {
627 * We can safely run softirq on inline stack, as we are not deep
628 * in the task stack here.
638 #ifdef CONFIG_HOTPLUG_CPU
640 * tasklet_kill_immediate is called to remove a tasklet which can already be
641 * scheduled for execution on @cpu.
643 * Unlike tasklet_kill, this function removes the tasklet
644 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
646 * When this function is called, @cpu must be in the CPU_DEAD state.
648 void tasklet_kill_immediate(struct tasklet_struct
*t
, unsigned int cpu
)
650 struct tasklet_struct
**i
;
652 BUG_ON(cpu_online(cpu
));
653 BUG_ON(test_bit(TASKLET_STATE_RUN
, &t
->state
));
655 if (!test_bit(TASKLET_STATE_SCHED
, &t
->state
))
658 /* CPU is dead, so no lock needed. */
659 for (i
= &per_cpu(tasklet_vec
, cpu
).head
; *i
; i
= &(*i
)->next
) {
662 /* If this was the tail element, move the tail ptr */
664 per_cpu(tasklet_vec
, cpu
).tail
= i
;
671 static int takeover_tasklets(unsigned int cpu
)
673 /* CPU is dead, so no lock needed. */
676 /* Find end, append list for that CPU. */
677 if (&per_cpu(tasklet_vec
, cpu
).head
!= per_cpu(tasklet_vec
, cpu
).tail
) {
678 *__this_cpu_read(tasklet_vec
.tail
) = per_cpu(tasklet_vec
, cpu
).head
;
679 __this_cpu_write(tasklet_vec
.tail
, per_cpu(tasklet_vec
, cpu
).tail
);
680 per_cpu(tasklet_vec
, cpu
).head
= NULL
;
681 per_cpu(tasklet_vec
, cpu
).tail
= &per_cpu(tasklet_vec
, cpu
).head
;
683 raise_softirq_irqoff(TASKLET_SOFTIRQ
);
685 if (&per_cpu(tasklet_hi_vec
, cpu
).head
!= per_cpu(tasklet_hi_vec
, cpu
).tail
) {
686 *__this_cpu_read(tasklet_hi_vec
.tail
) = per_cpu(tasklet_hi_vec
, cpu
).head
;
687 __this_cpu_write(tasklet_hi_vec
.tail
, per_cpu(tasklet_hi_vec
, cpu
).tail
);
688 per_cpu(tasklet_hi_vec
, cpu
).head
= NULL
;
689 per_cpu(tasklet_hi_vec
, cpu
).tail
= &per_cpu(tasklet_hi_vec
, cpu
).head
;
691 raise_softirq_irqoff(HI_SOFTIRQ
);
697 #define takeover_tasklets NULL
698 #endif /* CONFIG_HOTPLUG_CPU */
700 static struct smp_hotplug_thread softirq_threads
= {
702 .thread_should_run
= ksoftirqd_should_run
,
703 .thread_fn
= run_ksoftirqd
,
704 .thread_comm
= "ksoftirqd/%u",
707 static __init
int spawn_ksoftirqd(void)
709 cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD
, "softirq:dead", NULL
,
711 BUG_ON(smpboot_register_percpu_thread(&softirq_threads
));
715 early_initcall(spawn_ksoftirqd
);
718 * [ These __weak aliases are kept in a separate compilation unit, so that
719 * GCC does not inline them incorrectly. ]
722 int __init __weak
early_irq_init(void)
727 int __init __weak
arch_probe_nr_irqs(void)
729 return NR_IRQS_LEGACY
;
732 int __init __weak
arch_early_irq_init(void)
737 unsigned int __weak
arch_dynirq_lower_bound(unsigned int from
)