1 // SPDX-License-Identifier: GPL-2.0-only
7  *	Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
20 #include <linux/cpu.h>
37    - No shared variables, all the data are CPU local.
38    - If a softirq needs serialization, let it serialize itself
40    - Even if softirq is serialized, only local cpu is marked for
41      execution. Hence, we get something sort of weak cpu binding.
46    - NET RX softirq. It is multithreaded and does not require
48    - NET TX softirq. It kicks software netdevice queues, hence
51    - Tasklets: serialized wrt itself.
64 	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
69  * we cannot loop indefinitely here to avoid userspace starvation,
94  * to a per CPU counter and to task::softirqs_disabled_cnt.
96  * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq
99  * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
109  * also in per CPU softirq_ctrl::cnt. This is necessary to allow tasks in a
116  * The per CPU counter prevents pointless wakeups of ksoftirqd in case that
129  * local_bh_blocked() - Check for idle whether BH processing is blocked
131  * Returns false if the per CPU softirq::cnt is 0 otherwise true.
135  * softirq_ctrl::lock was the only running task on the CPU and blocks on
151 	if (!current->softirq_disable_cnt) {  in __local_bh_disable_ip()
162 	 * Track the per CPU softirq disabled state. On RT this is per CPU  in __local_bh_disable_ip()
170 	current->softirq_disable_cnt = newcnt;  in __local_bh_disable_ip()
185 	DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=  in __local_bh_enable()
195 	current->softirq_disable_cnt = newcnt;  in __local_bh_enable()
228 	 * If this was called from non preemptible context, wake up the  in __local_bh_enable_ip()
252  * to acquire the per CPU local lock for reentrancy protection.
298  * This one is for softirq.c-internal use, where hardirqs are disabled
312 	 * is set and before current->softirq_enabled is cleared.  in __local_bh_disable_ip()
326 		current->preempt_disable_ip = get_lock_parent_ip();  in __local_bh_disable_ip()
348  * Special-case - softirqs can safely be enabled by __do_softirq(),
349  * without processing still-pending softirqs:
374 	__preempt_count_sub(cnt - 1);  in __local_bh_enable_ip()
470  * The two things to balance is latency against fairness -
481  * not miss-qualify lock contexts and miss possible deadlocks.
513 	unsigned long old_flags = current->flags;  in __do_softirq()
525 	current->flags &= ~PF_MEMALLOC;  in __do_softirq()
545 		h += softirq_bit - 1;  in __do_softirq()
547 		vec_nr = h - softirq_vec;  in __do_softirq()
553 		h->action(h);  in __do_softirq()
557 			       vec_nr, softirq_to_name[vec_nr], h->action,  in __do_softirq()
574 		    --max_restart)  in __do_softirq()
587  * irq_enter_rcu - Enter an interrupt context with RCU watching
601  * irq_enter - Enter an interrupt context including RCU update
612 	int cpu = smp_processor_id();  in tick_irq_exit()  local
614 	/* Make sure that timer wheel updates are propagated */  in tick_irq_exit()
615 	if ((sched_core_idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {  in tick_irq_exit()
638  * irq_exit_rcu() - Exit an interrupt context without updating RCU
650  * irq_exit - Exit an interrupt context, update RCU and lockdep
671 	 * (this also catches softirq-disabled code). We will  in raise_softirq_irqoff()
675 	 * Otherwise we wake up ksoftirqd to make sure we  in raise_softirq_irqoff()
723 	t->next = NULL;  in __tasklet_schedule_common()
724 	*head->tail = t;  in __tasklet_schedule_common()
725 	head->tail = &(t->next);  in __tasklet_schedule_common()
746 	if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {  in tasklet_clear_sched()
747 		wake_up_var(&t->state);  in tasklet_clear_sched()
752 		  t->use_callback ? "callback" : "func",  in tasklet_clear_sched()
753 		  t->use_callback ? (void *)t->callback : (void *)t->func);  in tasklet_clear_sched()
765 	list = tl_head->head;  in tasklet_action_common()
766 	tl_head->head = NULL;  in tasklet_action_common()
767 	tl_head->tail = &tl_head->head;  in tasklet_action_common()
773 		list = list->next;  in tasklet_action_common()
776 			if (!atomic_read(&t->count)) {  in tasklet_action_common()
778 					if (t->use_callback) {  in tasklet_action_common()
779 						trace_tasklet_entry(t, t->callback);  in tasklet_action_common()
780 						t->callback(t);  in tasklet_action_common()
781 						trace_tasklet_exit(t, t->callback);  in tasklet_action_common()
783 						trace_tasklet_entry(t, t->func);  in tasklet_action_common()
784 						t->func(t->data);  in tasklet_action_common()
785 						trace_tasklet_exit(t, t->func);  in tasklet_action_common()
795 		t->next = NULL;  in tasklet_action_common()
796 		*tl_head->tail = t;  in tasklet_action_common()
797 		tl_head->tail = &t->next;  in tasklet_action_common()
816 	t->next = NULL;  in tasklet_setup()
817 	t->state = 0;  in tasklet_setup()
818 	atomic_set(&t->count, 0);  in tasklet_setup()
819 	t->callback = callback;  in tasklet_setup()
820 	t->use_callback = true;  in tasklet_setup()
821 	t->data = 0;  in tasklet_setup()
828 	t->next = NULL;  in tasklet_init()
829 	t->state = 0;  in tasklet_init()
830 	atomic_set(&t->count, 0);  in tasklet_init()
831 	t->func = func;  in tasklet_init()
832 	t->use_callback = false;  in tasklet_init()
833 	t->data = data;  in tasklet_init()
844 	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {  in tasklet_unlock_spin_wait()
849 			 * running. If the tasklet runs on a different CPU  in tasklet_unlock_spin_wait()
868 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))  in tasklet_kill()
869 		wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));  in tasklet_kill()
880 	clear_bit(TASKLET_STATE_RUN, &t->state);  in tasklet_unlock()
882 	wake_up_var(&t->state);  in tasklet_unlock()
888 	wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));  in tasklet_unlock_wait()
895 	int cpu;  in softirq_init()  local
897 	for_each_possible_cpu(cpu) {  in softirq_init()
898 		per_cpu(tasklet_vec, cpu).tail =  in softirq_init()
899 			&per_cpu(tasklet_vec, cpu).head;  in softirq_init()
900 		per_cpu(tasklet_hi_vec, cpu).tail =  in softirq_init()
901 			&per_cpu(tasklet_hi_vec, cpu).head;  in softirq_init()
908 static int ksoftirqd_should_run(unsigned int cpu)  in ksoftirqd_should_run()  argument
913 static void run_ksoftirqd(unsigned int cpu)  in run_ksoftirqd()  argument
930 static int takeover_tasklets(unsigned int cpu)  in takeover_tasklets()  argument
932 	/* CPU is dead, so no lock needed. */  in takeover_tasklets()
935 	/* Find end, append list for that CPU. */  in takeover_tasklets()
936 	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {  in takeover_tasklets()
937 		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;  in takeover_tasklets()
938 		__this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);  in takeover_tasklets()
939 		per_cpu(tasklet_vec, cpu).head = NULL;  in takeover_tasklets()
940 		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;  in takeover_tasklets()
944 	if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {  in takeover_tasklets()
945 		*__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;  in takeover_tasklets()
946 		__this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);  in takeover_tasklets()
947 		per_cpu(tasklet_hi_vec, cpu).head = NULL;  in takeover_tasklets()
948 		per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;  in takeover_tasklets()