diff options
Diffstat (limited to 'kernel/softirq.c')
| -rw-r--r-- | kernel/softirq.c | 763 |
1 files changed, 763 insertions, 0 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c new file mode 100644 index 000000000..6f584861d --- /dev/null +++ b/kernel/softirq.c @@ -0,0 +1,763 @@ +/* + * linux/kernel/softirq.c + * + * Copyright (C) 1992 Linus Torvalds + * + * Distribute under GPLv2. + * + * Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903) + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/export.h> +#include <linux/kernel_stat.h> +#include <linux/interrupt.h> +#include <linux/init.h> +#include <linux/mm.h> +#include <linux/notifier.h> +#include <linux/percpu.h> +#include <linux/cpu.h> +#include <linux/freezer.h> +#include <linux/kthread.h> +#include <linux/rcupdate.h> +#include <linux/ftrace.h> +#include <linux/smp.h> +#include <linux/smpboot.h> +#include <linux/tick.h> +#include <linux/irq.h> + +#define CREATE_TRACE_POINTS +#include <trace/events/irq.h> + +/* + - No shared variables, all the data are CPU local. + - If a softirq needs serialization, let it serialize itself + by its own spinlocks. + - Even if softirq is serialized, only local cpu is marked for + execution. Hence, we get something sort of weak cpu binding. + Though it is still not clear, will it result in better locality + or will not. + + Examples: + - NET RX softirq. It is multithreaded and does not require + any global serialization. + - NET TX softirq. It kicks software netdevice queues, hence + it is logically serialized per device, but this serialization + is invisible to common code. + - Tasklets: serialized wrt itself. + */ + +#ifndef __ARCH_IRQ_STAT +DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat); +EXPORT_PER_CPU_SYMBOL(irq_stat); +#endif + +static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp; + +DEFINE_PER_CPU(struct task_struct *, ksoftirqd); + +const char * const softirq_to_name[NR_SOFTIRQS] = { + "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL", + "TASKLET", "SCHED", "HRTIMER", "RCU" +}; + +/* + * we cannot loop indefinitely here to avoid userspace starvation, + * but we also don't want to introduce a worst case 1/HZ latency + * to the pending events, so lets the scheduler to balance + * the softirq load for us. + */ +static void wakeup_softirqd(void) +{ + /* Interrupts are disabled: no need to stop preemption */ + struct task_struct *tsk = __this_cpu_read(ksoftirqd); + + if (tsk && tsk->state != TASK_RUNNING) + wake_up_process(tsk); +} + +/* + * If ksoftirqd is scheduled, we do not want to process pending softirqs + * right now. Let ksoftirqd handle this at its own rate, to get fairness, + * unless we're doing some of the synchronous softirqs. + */ +#define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ)) +static bool ksoftirqd_running(unsigned long pending) +{ + struct task_struct *tsk = __this_cpu_read(ksoftirqd); + + if (pending & SOFTIRQ_NOW_MASK) + return false; + return tsk && (tsk->state == TASK_RUNNING); +} + +/* + * preempt_count and SOFTIRQ_OFFSET usage: + * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving + * softirq processing. + * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET) + * on local_bh_disable or local_bh_enable. + * This lets us distinguish between whether we are currently processing + * softirq and whether we just have bh disabled. + */ + +/* + * This one is for softirq.c-internal use, + * where hardirqs are disabled legitimately: + */ +#ifdef CONFIG_TRACE_IRQFLAGS +void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) +{ + unsigned long flags; + + WARN_ON_ONCE(in_irq()); + + raw_local_irq_save(flags); + /* + * The preempt tracer hooks into preempt_count_add and will break + * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET + * is set and before current->softirq_enabled is cleared. + * We must manually increment preempt_count here and manually + * call the trace_preempt_off later. + */ + __preempt_count_add(cnt); + /* + * Were softirqs turned off above: + */ + if (softirq_count() == (cnt & SOFTIRQ_MASK)) + trace_softirqs_off(ip); + raw_local_irq_restore(flags); + + if (preempt_count() == cnt) { +#ifdef CONFIG_DEBUG_PREEMPT + current->preempt_disable_ip = get_lock_parent_ip(); +#endif + trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip()); + } +} +EXPORT_SYMBOL(__local_bh_disable_ip); +#endif /* CONFIG_TRACE_IRQFLAGS */ + +static void __local_bh_enable(unsigned int cnt) +{ + lockdep_assert_irqs_disabled(); + + if (preempt_count() == cnt) + trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip()); + + if (softirq_count() == (cnt & SOFTIRQ_MASK)) + trace_softirqs_on(_RET_IP_); + + __preempt_count_sub(cnt); +} + +/* + * Special-case - softirqs can safely be enabled by __do_softirq(), + * without processing still-pending softirqs: + */ +void _local_bh_enable(void) +{ + WARN_ON_ONCE(in_irq()); + __local_bh_enable(SOFTIRQ_DISABLE_OFFSET); +} +EXPORT_SYMBOL(_local_bh_enable); + +void __local_bh_enable_ip(unsigned long ip, unsigned int cnt) +{ + WARN_ON_ONCE(in_irq()); + lockdep_assert_irqs_enabled(); +#ifdef CONFIG_TRACE_IRQFLAGS + local_irq_disable(); +#endif + /* + * Are softirqs going to be turned on now: + */ + if (softirq_count() == SOFTIRQ_DISABLE_OFFSET) + trace_softirqs_on(ip); + /* + * Keep preemption disabled until we are done with + * softirq processing: + */ + preempt_count_sub(cnt - 1); + + if (unlikely(!in_interrupt() && local_softirq_pending())) { + /* + * Run softirq if any pending. And do it in its own stack + * as we may be calling this deep in a task call stack already. + */ + do_softirq(); + } + + preempt_count_dec(); +#ifdef CONFIG_TRACE_IRQFLAGS + local_irq_enable(); +#endif + preempt_check_resched(); +} +EXPORT_SYMBOL(__local_bh_enable_ip); + +/* + * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, + * but break the loop if need_resched() is set or after 2 ms. + * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in + * certain cases, such as stop_machine(), jiffies may cease to + * increment and so we need the MAX_SOFTIRQ_RESTART limit as + * well to make sure we eventually return from this method. + * + * These limits have been established via experimentation. + * The two things to balance is latency against fairness - + * we want to handle softirqs as soon as possible, but they + * should not be able to lock up the box. + */ +#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) +#define MAX_SOFTIRQ_RESTART 10 + +#ifdef CONFIG_TRACE_IRQFLAGS +/* + * When we run softirqs from irq_exit() and thus on the hardirq stack we need + * to keep the lockdep irq context tracking as tight as possible in order to + * not miss-qualify lock contexts and miss possible deadlocks. + */ + +static inline bool lockdep_softirq_start(void) +{ + bool in_hardirq = false; + + if (trace_hardirq_context(current)) { + in_hardirq = true; + trace_hardirq_exit(); + } + + lockdep_softirq_enter(); + + return in_hardirq; +} + +static inline void lockdep_softirq_end(bool in_hardirq) +{ + lockdep_softirq_exit(); + + if (in_hardirq) + trace_hardirq_enter(); +} +#else +static inline bool lockdep_softirq_start(void) { return false; } +static inline void lockdep_softirq_end(bool in_hardirq) { } +#endif + +asmlinkage __visible void __softirq_entry __do_softirq(void) +{ + unsigned long end = jiffies + MAX_SOFTIRQ_TIME; + unsigned long old_flags = current->flags; + int max_restart = MAX_SOFTIRQ_RESTART; + struct softirq_action *h; + bool in_hardirq; + __u32 pending; + int softirq_bit; + + /* + * Mask out PF_MEMALLOC s current task context is borrowed for the + * softirq. A softirq handled such as network RX might set PF_MEMALLOC + * again if the socket is related to swap + */ + current->flags &= ~PF_MEMALLOC; + + pending = local_softirq_pending(); + account_irq_enter_time(current); + + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET); + in_hardirq = lockdep_softirq_start(); + +restart: + /* Reset the pending bitmask before enabling irqs */ + set_softirq_pending(0); + + local_irq_enable(); + + h = softirq_vec; + + while ((softirq_bit = ffs(pending))) { + unsigned int vec_nr; + int prev_count; + + h += softirq_bit - 1; + + vec_nr = h - softirq_vec; + prev_count = preempt_count(); + + kstat_incr_softirqs_this_cpu(vec_nr); + + trace_softirq_entry(vec_nr); + h->action(h); + trace_softirq_exit(vec_nr); + if (unlikely(prev_count != preempt_count())) { + pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n", + vec_nr, softirq_to_name[vec_nr], h->action, + prev_count, preempt_count()); + preempt_count_set(prev_count); + } + h++; + pending >>= softirq_bit; + } + + rcu_bh_qs(); + local_irq_disable(); + + pending = local_softirq_pending(); + if (pending) { + if (time_before(jiffies, end) && !need_resched() && + --max_restart) + goto restart; + + wakeup_softirqd(); + } + + lockdep_softirq_end(in_hardirq); + account_irq_exit_time(current); + __local_bh_enable(SOFTIRQ_OFFSET); + WARN_ON_ONCE(in_interrupt()); + current_restore_flags(old_flags, PF_MEMALLOC); +} + +asmlinkage __visible void do_softirq(void) +{ + __u32 pending; + unsigned long flags; + + if (in_interrupt()) + return; + + local_irq_save(flags); + + pending = local_softirq_pending(); + + if (pending && !ksoftirqd_running(pending)) + do_softirq_own_stack(); + + local_irq_restore(flags); +} + +/* + * Enter an interrupt context. + */ +void irq_enter(void) +{ + rcu_irq_enter(); + if (is_idle_task(current) && !in_interrupt()) { + /* + * Prevent raise_softirq from needlessly waking up ksoftirqd + * here, as softirq will be serviced on return from interrupt. + */ + local_bh_disable(); + tick_irq_enter(); + _local_bh_enable(); + } + + __irq_enter(); +} + +static inline void invoke_softirq(void) +{ + if (ksoftirqd_running(local_softirq_pending())) + return; + + if (!force_irqthreads) { +#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK + /* + * We can safely execute softirq on the current stack if + * it is the irq stack, because it should be near empty + * at this stage. + */ + __do_softirq(); +#else + /* + * Otherwise, irq_exit() is called on the task stack that can + * be potentially deep already. So call softirq in its own stack + * to prevent from any overrun. + */ + do_softirq_own_stack(); +#endif + } else { + wakeup_softirqd(); + } +} + +static inline void tick_irq_exit(void) +{ +#ifdef CONFIG_NO_HZ_COMMON + int cpu = smp_processor_id(); + + /* Make sure that timer wheel updates are propagated */ + if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) { + if (!in_irq()) + tick_nohz_irq_exit(); + } +#endif +} + +/* + * Exit an interrupt context. Process softirqs if needed and possible: + */ +void irq_exit(void) +{ +#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED + local_irq_disable(); +#else + lockdep_assert_irqs_disabled(); +#endif + account_irq_exit_time(current); + preempt_count_sub(HARDIRQ_OFFSET); + if (!in_interrupt() && local_softirq_pending()) + invoke_softirq(); + + tick_irq_exit(); + rcu_irq_exit(); + trace_hardirq_exit(); /* must be last! */ +} + +/* + * This function must run with irqs disabled! + */ +inline void raise_softirq_irqoff(unsigned int nr) +{ + __raise_softirq_irqoff(nr); + + /* + * If we're in an interrupt or softirq, we're done + * (this also catches softirq-disabled code). We will + * actually run the softirq once we return from + * the irq or softirq. + * + * Otherwise we wake up ksoftirqd to make sure we + * schedule the softirq soon. + */ + if (!in_interrupt()) + wakeup_softirqd(); +} + +void raise_softirq(unsigned int nr) +{ + unsigned long flags; + + local_irq_save(flags); + raise_softirq_irqoff(nr); + local_irq_restore(flags); +} + +void __raise_softirq_irqoff(unsigned int nr) +{ + trace_softirq_raise(nr); + or_softirq_pending(1UL << nr); +} + +void open_softirq(int nr, void (*action)(struct softirq_action *)) +{ + softirq_vec[nr].action = action; +} + +/* + * Tasklets + */ +struct tasklet_head { + struct tasklet_struct *head; + struct tasklet_struct **tail; +}; + +static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec); +static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec); + +static void __tasklet_schedule_common(struct tasklet_struct *t, + struct tasklet_head __percpu *headp, + unsigned int softirq_nr) +{ + struct tasklet_head *head; + unsigned long flags; + + local_irq_save(flags); + head = this_cpu_ptr(headp); + t->next = NULL; + *head->tail = t; + head->tail = &(t->next); + raise_softirq_irqoff(softirq_nr); + local_irq_restore(flags); +} + +void __tasklet_schedule(struct tasklet_struct *t) +{ + __tasklet_schedule_common(t, &tasklet_vec, + TASKLET_SOFTIRQ); +} +EXPORT_SYMBOL(__tasklet_schedule); + +void __tasklet_hi_schedule(struct tasklet_struct *t) +{ + __tasklet_schedule_common(t, &tasklet_hi_vec, + HI_SOFTIRQ); +} +EXPORT_SYMBOL(__tasklet_hi_schedule); + +static void tasklet_action_common(struct softirq_action *a, + struct tasklet_head *tl_head, + unsigned int softirq_nr) +{ + struct tasklet_struct *list; + + local_irq_disable(); + list = tl_head->head; + tl_head->head = NULL; + tl_head->tail = &tl_head->head; + local_irq_enable(); + + while (list) { + struct tasklet_struct *t = list; + + list = list->next; + + if (tasklet_trylock(t)) { + if (!atomic_read(&t->count)) { + if (!test_and_clear_bit(TASKLET_STATE_SCHED, + &t->state)) + BUG(); + t->func(t->data); + tasklet_unlock(t); + continue; + } + tasklet_unlock(t); + } + + local_irq_disable(); + t->next = NULL; + *tl_head->tail = t; + tl_head->tail = &t->next; + __raise_softirq_irqoff(softirq_nr); + local_irq_enable(); + } +} + +static __latent_entropy void tasklet_action(struct softirq_action *a) +{ + tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ); +} + +static __latent_entropy void tasklet_hi_action(struct softirq_action *a) +{ + tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ); +} + +void tasklet_init(struct tasklet_struct *t, + void (*func)(unsigned long), unsigned long data) +{ + t->next = NULL; + t->state = 0; + atomic_set(&t->count, 0); + t->func = func; + t->data = data; +} +EXPORT_SYMBOL(tasklet_init); + +void tasklet_kill(struct tasklet_struct *t) +{ + if (in_interrupt()) + pr_notice("Attempt to kill tasklet from interrupt\n"); + + while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { + do { + yield(); + } while (test_bit(TASKLET_STATE_SCHED, &t->state)); + } + tasklet_unlock_wait(t); + clear_bit(TASKLET_STATE_SCHED, &t->state); +} +EXPORT_SYMBOL(tasklet_kill); + +/* + * tasklet_hrtimer + */ + +/* + * The trampoline is called when the hrtimer expires. It schedules a tasklet + * to run __tasklet_hrtimer_trampoline() which in turn will call the intended + * hrtimer callback, but from softirq context. + */ +static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer) +{ + struct tasklet_hrtimer *ttimer = + container_of(timer, struct tasklet_hrtimer, timer); + + tasklet_hi_schedule(&ttimer->tasklet); + return HRTIMER_NORESTART; +} + +/* + * Helper function which calls the hrtimer callback from + * tasklet/softirq context + */ +static void __tasklet_hrtimer_trampoline(unsigned long data) +{ + struct tasklet_hrtimer *ttimer = (void *)data; + enum hrtimer_restart restart; + + restart = ttimer->function(&ttimer->timer); + if (restart != HRTIMER_NORESTART) + hrtimer_restart(&ttimer->timer); +} + +/** + * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks + * @ttimer: tasklet_hrtimer which is initialized + * @function: hrtimer callback function which gets called from softirq context + * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME) + * @mode: hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL) + */ +void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer, + enum hrtimer_restart (*function)(struct hrtimer *), + clockid_t which_clock, enum hrtimer_mode mode) +{ + hrtimer_init(&ttimer->timer, which_clock, mode); + ttimer->timer.function = __hrtimer_tasklet_trampoline; + tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline, + (unsigned long)ttimer); + ttimer->function = function; +} +EXPORT_SYMBOL_GPL(tasklet_hrtimer_init); + +void __init softirq_init(void) +{ + int cpu; + + for_each_possible_cpu(cpu) { + per_cpu(tasklet_vec, cpu).tail = + &per_cpu(tasklet_vec, cpu).head; + per_cpu(tasklet_hi_vec, cpu).tail = + &per_cpu(tasklet_hi_vec, cpu).head; + } + + open_softirq(TASKLET_SOFTIRQ, tasklet_action); + open_softirq(HI_SOFTIRQ, tasklet_hi_action); +} + +static int ksoftirqd_should_run(unsigned int cpu) +{ + return local_softirq_pending(); +} + +static void run_ksoftirqd(unsigned int cpu) +{ + local_irq_disable(); + if (local_softirq_pending()) { + /* + * We can safely run softirq on inline stack, as we are not deep + * in the task stack here. + */ + __do_softirq(); + local_irq_enable(); + cond_resched(); + return; + } + local_irq_enable(); +} + +#ifdef CONFIG_HOTPLUG_CPU +/* + * tasklet_kill_immediate is called to remove a tasklet which can already be + * scheduled for execution on @cpu. + * + * Unlike tasklet_kill, this function removes the tasklet + * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state. + * + * When this function is called, @cpu must be in the CPU_DEAD state. + */ +void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu) +{ + struct tasklet_struct **i; + + BUG_ON(cpu_online(cpu)); + BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state)); + + if (!test_bit(TASKLET_STATE_SCHED, &t->state)) + return; + + /* CPU is dead, so no lock needed. */ + for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) { + if (*i == t) { + *i = t->next; + /* If this was the tail element, move the tail ptr */ + if (*i == NULL) + per_cpu(tasklet_vec, cpu).tail = i; + return; + } + } + BUG(); +} + +static int takeover_tasklets(unsigned int cpu) +{ + /* CPU is dead, so no lock needed. */ + local_irq_disable(); + + /* Find end, append list for that CPU. */ + if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) { + *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head; + this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail); + per_cpu(tasklet_vec, cpu).head = NULL; + per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head; + } + raise_softirq_irqoff(TASKLET_SOFTIRQ); + + if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) { + *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head; + __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail); + per_cpu(tasklet_hi_vec, cpu).head = NULL; + per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head; + } + raise_softirq_irqoff(HI_SOFTIRQ); + + local_irq_enable(); + return 0; +} +#else +#define takeover_tasklets NULL +#endif /* CONFIG_HOTPLUG_CPU */ + +static struct smp_hotplug_thread softirq_threads = { + .store = &ksoftirqd, + .thread_should_run = ksoftirqd_should_run, + .thread_fn = run_ksoftirqd, + .thread_comm = "ksoftirqd/%u", +}; + +static __init int spawn_ksoftirqd(void) +{ + cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL, + takeover_tasklets); + BUG_ON(smpboot_register_percpu_thread(&softirq_threads)); + + return 0; +} +early_initcall(spawn_ksoftirqd); + +/* + * [ These __weak aliases are kept in a separate compilation unit, so that + * GCC does not inline them incorrectly. ] + */ + +int __init __weak early_irq_init(void) +{ + return 0; +} + +int __init __weak arch_probe_nr_irqs(void) +{ + return NR_IRQS_LEGACY; +} + +int __init __weak arch_early_irq_init(void) +{ + return 0; +} + +unsigned int __weak arch_dynirq_lower_bound(unsigned int from) +{ + return from; +} |