diff options
Diffstat (limited to 'kernel/softirq.c')
| -rw-r--r-- | kernel/softirq.c | 575 |
1 files changed, 462 insertions, 113 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index 2c71d91efff0..85bcdc534d16 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -21,9 +21,11 @@ #include <linux/freezer.h> #include <linux/kthread.h> #include <linux/rcupdate.h> +#include <linux/delay.h> #include <linux/ftrace.h> #include <linux/smp.h> #include <linux/tick.h> +#include <linux/locallock.h> #define CREATE_TRACE_POINTS #include <trace/events/irq.h> @@ -61,6 +63,67 @@ char *softirq_to_name[NR_SOFTIRQS] = { "TASKLET", "SCHED", "HRTIMER", "RCU" }; +#ifdef CONFIG_NO_HZ +# ifdef CONFIG_PREEMPT_RT_FULL +/* + * On preempt-rt a softirq might be blocked on a lock. There might be + * no other runnable task on this CPU because the lock owner runs on + * some other CPU. So we have to go into idle with the pending bit + * set. Therefor we need to check this otherwise we warn about false + * positives which confuses users and defeats the whole purpose of + * this test. + * + * This code is called with interrupts disabled. + */ +void softirq_check_pending_idle(void) +{ + static int rate_limit; + u32 warnpending = 0, pending = local_softirq_pending(); + + if (rate_limit >= 10) + return; + + if (pending) { + struct task_struct *tsk; + + tsk = __get_cpu_var(ksoftirqd); + /* + * The wakeup code in rtmutex.c wakes up the task + * _before_ it sets pi_blocked_on to NULL under + * tsk->pi_lock. So we need to check for both: state + * and pi_blocked_on. + */ + raw_spin_lock(&tsk->pi_lock); + + if (!tsk->pi_blocked_on && !(tsk->state == TASK_RUNNING)) + warnpending = 1; + + raw_spin_unlock(&tsk->pi_lock); + } + + if (warnpending) { + printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", + pending); + rate_limit++; + } +} +# else +/* + * On !PREEMPT_RT we just printk rate limited: + */ +void softirq_check_pending_idle(void) +{ + static int rate_limit; + + if (rate_limit < 10) { + printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", + local_softirq_pending()); + rate_limit++; + } +} +# endif +#endif + /* * we cannot loop indefinitely here to avoid userspace starvation, * but we also don't want to introduce a worst case 1/HZ latency @@ -76,6 +139,36 @@ static void wakeup_softirqd(void) wake_up_process(tsk); } +static void handle_pending_softirqs(u32 pending, int cpu, int need_rcu_bh_qs) +{ + struct softirq_action *h = softirq_vec; + unsigned int prev_count = preempt_count(); + + local_irq_enable(); + for ( ; pending; h++, pending >>= 1) { + unsigned int vec_nr = h - softirq_vec; + + if (!(pending & 1)) + continue; + + 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())) { + printk(KERN_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, (unsigned int) preempt_count()); + preempt_count() = prev_count; + } + if (need_rcu_bh_qs) + rcu_bh_qs(cpu); + } + local_irq_disable(); +} + +#ifndef CONFIG_PREEMPT_RT_FULL /* * preempt_count and SOFTIRQ_OFFSET usage: * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving @@ -206,7 +299,6 @@ EXPORT_SYMBOL(local_bh_enable_ip); asmlinkage void __do_softirq(void) { - struct softirq_action *h; __u32 pending; int max_restart = MAX_SOFTIRQ_RESTART; int cpu; @@ -215,7 +307,7 @@ asmlinkage void __do_softirq(void) account_system_vtime(current); __local_bh_disable((unsigned long)__builtin_return_address(0), - SOFTIRQ_OFFSET); + SOFTIRQ_OFFSET); lockdep_softirq_enter(); cpu = smp_processor_id(); @@ -223,36 +315,7 @@ restart: /* Reset the pending bitmask before enabling irqs */ set_softirq_pending(0); - local_irq_enable(); - - h = softirq_vec; - - do { - if (pending & 1) { - unsigned int vec_nr = h - softirq_vec; - int 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())) { - printk(KERN_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() = prev_count; - } - - rcu_bh_qs(cpu); - } - h++; - pending >>= 1; - } while (pending); - - local_irq_disable(); + handle_pending_softirqs(pending, cpu, 1); pending = local_softirq_pending(); if (pending && --max_restart) @@ -267,6 +330,26 @@ restart: __local_bh_enable(SOFTIRQ_OFFSET); } +/* + * Called with preemption disabled from run_ksoftirqd() + */ +static int ksoftirqd_do_softirq(int cpu) +{ + /* + * Preempt disable stops cpu going offline. + * If already offline, we'll be on wrong CPU: + * don't process. + */ + if (cpu_is_offline(cpu)) + return -1; + + local_irq_disable(); + if (local_softirq_pending()) + __do_softirq(); + local_irq_enable(); + return 0; +} + #ifndef __ARCH_HAS_DO_SOFTIRQ asmlinkage void do_softirq(void) @@ -289,6 +372,184 @@ asmlinkage void do_softirq(void) #endif +static inline void local_bh_disable_nort(void) { local_bh_disable(); } +static inline void _local_bh_enable_nort(void) { _local_bh_enable(); } +static inline void ksoftirqd_set_sched_params(void) { } +static inline void ksoftirqd_clr_sched_params(void) { } + +#else /* !PREEMPT_RT_FULL */ + +/* + * On RT we serialize softirq execution with a cpu local lock + */ +static DEFINE_LOCAL_IRQ_LOCK(local_softirq_lock); +static DEFINE_PER_CPU(struct task_struct *, local_softirq_runner); + +static void __do_softirq_common(int need_rcu_bh_qs); + +void __do_softirq(void) +{ + __do_softirq_common(0); +} + +void __init softirq_early_init(void) +{ + local_irq_lock_init(local_softirq_lock); +} + +void local_bh_disable(void) +{ + migrate_disable(); + current->softirq_nestcnt++; +} +EXPORT_SYMBOL(local_bh_disable); + +void local_bh_enable(void) +{ + if (WARN_ON(current->softirq_nestcnt == 0)) + return; + + if ((current->softirq_nestcnt == 1) && + local_softirq_pending() && + local_trylock(local_softirq_lock)) { + + local_irq_disable(); + if (local_softirq_pending()) + __do_softirq(); + local_irq_enable(); + local_unlock(local_softirq_lock); + WARN_ON(current->softirq_nestcnt != 1); + } + current->softirq_nestcnt--; + migrate_enable(); +} +EXPORT_SYMBOL(local_bh_enable); + +void local_bh_enable_ip(unsigned long ip) +{ + local_bh_enable(); +} +EXPORT_SYMBOL(local_bh_enable_ip); + +/* For tracing */ +int notrace __in_softirq(void) +{ + if (__get_cpu_var(local_softirq_lock).owner == current) + return __get_cpu_var(local_softirq_lock).nestcnt; + return 0; +} + +int in_serving_softirq(void) +{ + int res; + + preempt_disable(); + res = __get_cpu_var(local_softirq_runner) == current; + preempt_enable(); + return res; +} +EXPORT_SYMBOL(in_serving_softirq); + +/* + * Called with bh and local interrupts disabled. For full RT cpu must + * be pinned. + */ +static void __do_softirq_common(int need_rcu_bh_qs) +{ + u32 pending = local_softirq_pending(); + int cpu = smp_processor_id(); + + current->softirq_nestcnt++; + + /* Reset the pending bitmask before enabling irqs */ + set_softirq_pending(0); + + __get_cpu_var(local_softirq_runner) = current; + + lockdep_softirq_enter(); + + handle_pending_softirqs(pending, cpu, need_rcu_bh_qs); + + pending = local_softirq_pending(); + if (pending) + wakeup_softirqd(); + + lockdep_softirq_exit(); + __get_cpu_var(local_softirq_runner) = NULL; + + current->softirq_nestcnt--; +} + +static int __thread_do_softirq(int cpu) +{ + /* + * Prevent the current cpu from going offline. + * pin_current_cpu() can reenable preemption and block on the + * hotplug mutex. When it returns, the current cpu is + * pinned. It might be the wrong one, but the offline check + * below catches that. + */ + pin_current_cpu(); + /* + * If called from ksoftirqd (cpu >= 0) we need to check + * whether we are on the wrong cpu due to cpu offlining. If + * called via thread_do_softirq() no action required. + */ + if (cpu >= 0 && cpu_is_offline(cpu)) { + unpin_current_cpu(); + return -1; + } + preempt_enable(); + local_lock(local_softirq_lock); + local_irq_disable(); + /* + * We cannot switch stacks on RT as we want to be able to + * schedule! + */ + if (local_softirq_pending()) + __do_softirq_common(cpu >= 0); + local_unlock(local_softirq_lock); + unpin_current_cpu(); + preempt_disable(); + local_irq_enable(); + return 0; +} + +/* + * Called from netif_rx_ni(). Preemption enabled. + */ +void thread_do_softirq(void) +{ + if (!in_serving_softirq()) { + preempt_disable(); + __thread_do_softirq(-1); + preempt_enable(); + } +} + +static int ksoftirqd_do_softirq(int cpu) +{ + return __thread_do_softirq(cpu); +} + +static inline void local_bh_disable_nort(void) { } +static inline void _local_bh_enable_nort(void) { } + +static inline void ksoftirqd_set_sched_params(void) +{ + struct sched_param param = { .sched_priority = 1 }; + + sched_setscheduler(current, SCHED_FIFO, ¶m); +} + +static inline void ksoftirqd_clr_sched_params(void) +{ + struct sched_param param = { .sched_priority = 0 }; + + sched_setscheduler(current, SCHED_NORMAL, ¶m); +} + +#endif /* PREEMPT_RT_FULL */ /* * Enter an interrupt context. */ @@ -302,9 +563,9 @@ void irq_enter(void) * Prevent raise_softirq from needlessly waking up ksoftirqd * here, as softirq will be serviced on return from interrupt. */ - local_bh_disable(); + local_bh_disable_nort(); tick_check_idle(cpu); - _local_bh_enable(); + _local_bh_enable_nort(); } __irq_enter(); @@ -313,6 +574,7 @@ void irq_enter(void) #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED static inline void invoke_softirq(void) { +#ifndef CONFIG_PREEMPT_RT_FULL if (!force_irqthreads) __do_softirq(); else { @@ -321,10 +583,14 @@ static inline void invoke_softirq(void) wakeup_softirqd(); __local_bh_enable(SOFTIRQ_OFFSET); } +#else + wakeup_softirqd(); +#endif } #else static inline void invoke_softirq(void) { +#ifndef CONFIG_PREEMPT_RT_FULL if (!force_irqthreads) do_softirq(); else { @@ -333,6 +599,9 @@ static inline void invoke_softirq(void) wakeup_softirqd(); __local_bh_enable(SOFTIRQ_OFFSET); } +#else + wakeup_softirqd(); +#endif } #endif @@ -353,7 +622,7 @@ void irq_exit(void) if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched()) tick_nohz_stop_sched_tick(0); #endif - preempt_enable_no_resched(); + __preempt_enable_no_resched(); } /* @@ -402,15 +671,45 @@ struct tasklet_head static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec); static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec); +static void inline +__tasklet_common_schedule(struct tasklet_struct *t, struct tasklet_head *head, unsigned int nr) +{ + if (tasklet_trylock(t)) { +again: + /* We may have been preempted before tasklet_trylock + * and __tasklet_action may have already run. + * So double check the sched bit while the takslet + * is locked before adding it to the list. + */ + if (test_bit(TASKLET_STATE_SCHED, &t->state)) { + t->next = NULL; + *head->tail = t; + head->tail = &(t->next); + raise_softirq_irqoff(nr); + tasklet_unlock(t); + } else { + /* This is subtle. If we hit the corner case above + * It is possible that we get preempted right here, + * and another task has successfully called + * tasklet_schedule(), then this function, and + * failed on the trylock. Thus we must be sure + * before releasing the tasklet lock, that the + * SCHED_BIT is clear. Otherwise the tasklet + * may get its SCHED_BIT set, but not added to the + * list + */ + if (!tasklet_tryunlock(t)) + goto again; + } + } +} + void __tasklet_schedule(struct tasklet_struct *t) { unsigned long flags; local_irq_save(flags); - t->next = NULL; - *__this_cpu_read(tasklet_vec.tail) = t; - __this_cpu_write(tasklet_vec.tail, &(t->next)); - raise_softirq_irqoff(TASKLET_SOFTIRQ); + __tasklet_common_schedule(t, &__get_cpu_var(tasklet_vec), TASKLET_SOFTIRQ); local_irq_restore(flags); } @@ -421,10 +720,7 @@ void __tasklet_hi_schedule(struct tasklet_struct *t) unsigned long flags; local_irq_save(flags); - t->next = NULL; - *__this_cpu_read(tasklet_hi_vec.tail) = t; - __this_cpu_write(tasklet_hi_vec.tail, &(t->next)); - raise_softirq_irqoff(HI_SOFTIRQ); + __tasklet_common_schedule(t, &__get_cpu_var(tasklet_hi_vec), HI_SOFTIRQ); local_irq_restore(flags); } @@ -432,50 +728,119 @@ EXPORT_SYMBOL(__tasklet_hi_schedule); void __tasklet_hi_schedule_first(struct tasklet_struct *t) { - BUG_ON(!irqs_disabled()); - - t->next = __this_cpu_read(tasklet_hi_vec.head); - __this_cpu_write(tasklet_hi_vec.head, t); - __raise_softirq_irqoff(HI_SOFTIRQ); + __tasklet_hi_schedule(t); } EXPORT_SYMBOL(__tasklet_hi_schedule_first); -static void tasklet_action(struct softirq_action *a) +void tasklet_enable(struct tasklet_struct *t) { - struct tasklet_struct *list; + if (!atomic_dec_and_test(&t->count)) + return; + if (test_and_clear_bit(TASKLET_STATE_PENDING, &t->state)) + tasklet_schedule(t); +} - local_irq_disable(); - list = __this_cpu_read(tasklet_vec.head); - __this_cpu_write(tasklet_vec.head, NULL); - __this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head); - local_irq_enable(); +EXPORT_SYMBOL(tasklet_enable); + +void tasklet_hi_enable(struct tasklet_struct *t) +{ + if (!atomic_dec_and_test(&t->count)) + return; + if (test_and_clear_bit(TASKLET_STATE_PENDING, &t->state)) + tasklet_hi_schedule(t); +} + +EXPORT_SYMBOL(tasklet_hi_enable); + +static void +__tasklet_action(struct softirq_action *a, struct tasklet_struct *list) +{ + int loops = 1000000; 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); + /* + * Should always succeed - after a tasklist got on the + * list (after getting the SCHED bit set from 0 to 1), + * nothing but the tasklet softirq it got queued to can + * lock it: + */ + if (!tasklet_trylock(t)) { + WARN_ON(1); + continue; } - local_irq_disable(); t->next = NULL; - *__this_cpu_read(tasklet_vec.tail) = t; - __this_cpu_write(tasklet_vec.tail, &(t->next)); - __raise_softirq_irqoff(TASKLET_SOFTIRQ); - local_irq_enable(); + + /* + * If we cannot handle the tasklet because it's disabled, + * mark it as pending. tasklet_enable() will later + * re-schedule the tasklet. + */ + if (unlikely(atomic_read(&t->count))) { +out_disabled: + /* implicit unlock: */ + wmb(); + t->state = TASKLET_STATEF_PENDING; + continue; + } + + /* + * After this point on the tasklet might be rescheduled + * on another CPU, but it can only be added to another + * CPU's tasklet list if we unlock the tasklet (which we + * dont do yet). + */ + if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) + WARN_ON(1); + +again: + t->func(t->data); + + /* + * Try to unlock the tasklet. We must use cmpxchg, because + * another CPU might have scheduled or disabled the tasklet. + * We only allow the STATE_RUN -> 0 transition here. + */ + while (!tasklet_tryunlock(t)) { + /* + * If it got disabled meanwhile, bail out: + */ + if (atomic_read(&t->count)) + goto out_disabled; + /* + * If it got scheduled meanwhile, re-execute + * the tasklet function: + */ + if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) + goto again; + if (!--loops) { + printk("hm, tasklet state: %08lx\n", t->state); + WARN_ON(1); + tasklet_unlock(t); + break; + } + } } } +static void tasklet_action(struct softirq_action *a) +{ + struct tasklet_struct *list; + + local_irq_disable(); + list = __get_cpu_var(tasklet_vec).head; + __get_cpu_var(tasklet_vec).head = NULL; + __get_cpu_var(tasklet_vec).tail = &__get_cpu_var(tasklet_vec).head; + local_irq_enable(); + + __tasklet_action(a, list); +} + static void tasklet_hi_action(struct softirq_action *a) { struct tasklet_struct *list; @@ -486,29 +851,7 @@ static void tasklet_hi_action(struct softirq_action *a) __this_cpu_write(tasklet_hi_vec.tail, &__get_cpu_var(tasklet_hi_vec).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; - *__this_cpu_read(tasklet_hi_vec.tail) = t; - __this_cpu_write(tasklet_hi_vec.tail, &(t->next)); - __raise_softirq_irqoff(HI_SOFTIRQ); - local_irq_enable(); - } + __tasklet_action(a, list); } @@ -531,7 +874,7 @@ void tasklet_kill(struct tasklet_struct *t) while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { do { - yield(); + msleep(1); } while (test_bit(TASKLET_STATE_SCHED, &t->state)); } tasklet_unlock_wait(t); @@ -737,31 +1080,40 @@ void __init softirq_init(void) open_softirq(HI_SOFTIRQ, tasklet_hi_action); } +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL) +void tasklet_unlock_wait(struct tasklet_struct *t) +{ + while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { + /* + * Hack for now to avoid this busy-loop: + */ +#ifdef CONFIG_PREEMPT_RT_FULL + msleep(1); +#else + barrier(); +#endif + } +} +EXPORT_SYMBOL(tasklet_unlock_wait); +#endif + static int run_ksoftirqd(void * __bind_cpu) { + ksoftirqd_set_sched_params(); + set_current_state(TASK_INTERRUPTIBLE); while (!kthread_should_stop()) { preempt_disable(); - if (!local_softirq_pending()) { - preempt_enable_no_resched(); - schedule(); - preempt_disable(); - } + if (!local_softirq_pending()) + schedule_preempt_disabled(); __set_current_state(TASK_RUNNING); while (local_softirq_pending()) { - /* Preempt disable stops cpu going offline. - If already offline, we'll be on wrong CPU: - don't process */ - if (cpu_is_offline((long)__bind_cpu)) + if (ksoftirqd_do_softirq((long) __bind_cpu)) goto wait_to_die; - local_irq_disable(); - if (local_softirq_pending()) - __do_softirq(); - local_irq_enable(); - preempt_enable_no_resched(); + __preempt_enable_no_resched(); cond_resched(); preempt_disable(); rcu_note_context_switch((long)__bind_cpu); @@ -774,6 +1126,7 @@ static int run_ksoftirqd(void * __bind_cpu) wait_to_die: preempt_enable(); + ksoftirqd_clr_sched_params(); /* Wait for kthread_stop */ set_current_state(TASK_INTERRUPTIBLE); while (!kthread_should_stop()) { @@ -850,9 +1203,8 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb, int hotcpu = (unsigned long)hcpu; struct task_struct *p; - switch (action) { + switch (action & ~CPU_TASKS_FROZEN) { case CPU_UP_PREPARE: - case CPU_UP_PREPARE_FROZEN: p = kthread_create_on_node(run_ksoftirqd, hcpu, cpu_to_node(hotcpu), @@ -865,19 +1217,16 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb, per_cpu(ksoftirqd, hotcpu) = p; break; case CPU_ONLINE: - case CPU_ONLINE_FROZEN: wake_up_process(per_cpu(ksoftirqd, hotcpu)); break; #ifdef CONFIG_HOTPLUG_CPU case CPU_UP_CANCELED: - case CPU_UP_CANCELED_FROZEN: if (!per_cpu(ksoftirqd, hotcpu)) break; /* Unbind so it can run. Fall thru. */ kthread_bind(per_cpu(ksoftirqd, hotcpu), cpumask_any(cpu_online_mask)); - case CPU_DEAD: - case CPU_DEAD_FROZEN: { + case CPU_POST_DEAD: { static const struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 }; |