linux/kernel/softirq.c
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   1/*
   2 *      linux/kernel/softirq.c
   3 *
   4 *      Copyright (C) 1992 Linus Torvalds
   5 *
   6 *      Distribute under GPLv2.
   7 *
   8 *      Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
   9 *
  10 *      Remote softirq infrastructure is by Jens Axboe.
  11 */
  12
  13#include <linux/export.h>
  14#include <linux/kernel_stat.h>
  15#include <linux/interrupt.h>
  16#include <linux/init.h>
  17#include <linux/mm.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/smpboot.h>
  27#include <linux/tick.h>
  28
  29#define CREATE_TRACE_POINTS
  30#include <trace/events/irq.h>
  31
  32#include <asm/irq.h>
  33/*
  34   - No shared variables, all the data are CPU local.
  35   - If a softirq needs serialization, let it serialize itself
  36     by its own spinlocks.
  37   - Even if softirq is serialized, only local cpu is marked for
  38     execution. Hence, we get something sort of weak cpu binding.
  39     Though it is still not clear, will it result in better locality
  40     or will not.
  41
  42   Examples:
  43   - NET RX softirq. It is multithreaded and does not require
  44     any global serialization.
  45   - NET TX softirq. It kicks software netdevice queues, hence
  46     it is logically serialized per device, but this serialization
  47     is invisible to common code.
  48   - Tasklets: serialized wrt itself.
  49 */
  50
  51#ifndef __ARCH_IRQ_STAT
  52irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
  53EXPORT_SYMBOL(irq_stat);
  54#endif
  55
  56static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
  57
  58DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  59
  60char *softirq_to_name[NR_SOFTIRQS] = {
  61        "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
  62        "TASKLET", "SCHED", "HRTIMER", "RCU"
  63};
  64
  65/*
  66 * we cannot loop indefinitely here to avoid userspace starvation,
  67 * but we also don't want to introduce a worst case 1/HZ latency
  68 * to the pending events, so lets the scheduler to balance
  69 * the softirq load for us.
  70 */
  71static void wakeup_softirqd(void)
  72{
  73        /* Interrupts are disabled: no need to stop preemption */
  74        struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  75
  76        if (tsk && tsk->state != TASK_RUNNING)
  77                wake_up_process(tsk);
  78}
  79
  80/*
  81 * preempt_count and SOFTIRQ_OFFSET usage:
  82 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
  83 *   softirq processing.
  84 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
  85 *   on local_bh_disable or local_bh_enable.
  86 * This lets us distinguish between whether we are currently processing
  87 * softirq and whether we just have bh disabled.
  88 */
  89
  90/*
  91 * This one is for softirq.c-internal use,
  92 * where hardirqs are disabled legitimately:
  93 */
  94#ifdef CONFIG_TRACE_IRQFLAGS
  95static void __local_bh_disable(unsigned long ip, unsigned int cnt)
  96{
  97        unsigned long flags;
  98
  99        WARN_ON_ONCE(in_irq());
 100
 101        raw_local_irq_save(flags);
 102        /*
 103         * The preempt tracer hooks into add_preempt_count and will break
 104         * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 105         * is set and before current->softirq_enabled is cleared.
 106         * We must manually increment preempt_count here and manually
 107         * call the trace_preempt_off later.
 108         */
 109        preempt_count() += cnt;
 110        /*
 111         * Were softirqs turned off above:
 112         */
 113        if (softirq_count() == cnt)
 114                trace_softirqs_off(ip);
 115        raw_local_irq_restore(flags);
 116
 117        if (preempt_count() == cnt)
 118                trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
 119}
 120#else /* !CONFIG_TRACE_IRQFLAGS */
 121static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
 122{
 123        add_preempt_count(cnt);
 124        barrier();
 125}
 126#endif /* CONFIG_TRACE_IRQFLAGS */
 127
 128void local_bh_disable(void)
 129{
 130        __local_bh_disable(_RET_IP_, SOFTIRQ_DISABLE_OFFSET);
 131}
 132
 133EXPORT_SYMBOL(local_bh_disable);
 134
 135static void __local_bh_enable(unsigned int cnt)
 136{
 137        WARN_ON_ONCE(in_irq());
 138        WARN_ON_ONCE(!irqs_disabled());
 139
 140        if (softirq_count() == cnt)
 141                trace_softirqs_on(_RET_IP_);
 142        sub_preempt_count(cnt);
 143}
 144
 145/*
 146 * Special-case - softirqs can safely be enabled in
 147 * cond_resched_softirq(), or by __do_softirq(),
 148 * without processing still-pending softirqs:
 149 */
 150void _local_bh_enable(void)
 151{
 152        __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 153}
 154
 155EXPORT_SYMBOL(_local_bh_enable);
 156
 157static inline void _local_bh_enable_ip(unsigned long ip)
 158{
 159        WARN_ON_ONCE(in_irq() || irqs_disabled());
 160#ifdef CONFIG_TRACE_IRQFLAGS
 161        local_irq_disable();
 162#endif
 163        /*
 164         * Are softirqs going to be turned on now:
 165         */
 166        if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 167                trace_softirqs_on(ip);
 168        /*
 169         * Keep preemption disabled until we are done with
 170         * softirq processing:
 171         */
 172        sub_preempt_count(SOFTIRQ_DISABLE_OFFSET - 1);
 173
 174        if (unlikely(!in_interrupt() && local_softirq_pending()))
 175                do_softirq();
 176
 177        dec_preempt_count();
 178#ifdef CONFIG_TRACE_IRQFLAGS
 179        local_irq_enable();
 180#endif
 181        preempt_check_resched();
 182}
 183
 184void local_bh_enable(void)
 185{
 186        _local_bh_enable_ip(_RET_IP_);
 187}
 188EXPORT_SYMBOL(local_bh_enable);
 189
 190void local_bh_enable_ip(unsigned long ip)
 191{
 192        _local_bh_enable_ip(ip);
 193}
 194EXPORT_SYMBOL(local_bh_enable_ip);
 195
 196/*
 197 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 198 * but break the loop if need_resched() is set or after 2 ms.
 199 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 200 * certain cases, such as stop_machine(), jiffies may cease to
 201 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 202 * well to make sure we eventually return from this method.
 203 *
 204 * These limits have been established via experimentation.
 205 * The two things to balance is latency against fairness -
 206 * we want to handle softirqs as soon as possible, but they
 207 * should not be able to lock up the box.
 208 */
 209#define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 210#define MAX_SOFTIRQ_RESTART 10
 211
 212asmlinkage void __do_softirq(void)
 213{
 214        struct softirq_action *h;
 215        __u32 pending;
 216        unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 217        int cpu;
 218        unsigned long old_flags = current->flags;
 219        int max_restart = MAX_SOFTIRQ_RESTART;
 220
 221        /*
 222         * Mask out PF_MEMALLOC s current task context is borrowed for the
 223         * softirq. A softirq handled such as network RX might set PF_MEMALLOC
 224         * again if the socket is related to swap
 225         */
 226        current->flags &= ~PF_MEMALLOC;
 227
 228        pending = local_softirq_pending();
 229        account_irq_enter_time(current);
 230
 231        __local_bh_disable(_RET_IP_, SOFTIRQ_OFFSET);
 232        lockdep_softirq_enter();
 233
 234        cpu = smp_processor_id();
 235restart:
 236        /* Reset the pending bitmask before enabling irqs */
 237        set_softirq_pending(0);
 238
 239        local_irq_enable();
 240
 241        h = softirq_vec;
 242
 243        do {
 244                if (pending & 1) {
 245                        unsigned int vec_nr = h - softirq_vec;
 246                        int prev_count = preempt_count();
 247
 248                        kstat_incr_softirqs_this_cpu(vec_nr);
 249
 250                        trace_softirq_entry(vec_nr);
 251                        h->action(h);
 252                        trace_softirq_exit(vec_nr);
 253                        if (unlikely(prev_count != preempt_count())) {
 254                                printk(KERN_ERR "huh, entered softirq %u %s %p"
 255                                       "with preempt_count %08x,"
 256                                       " exited with %08x?\n", vec_nr,
 257                                       softirq_to_name[vec_nr], h->action,
 258                                       prev_count, preempt_count());
 259                                preempt_count() = prev_count;
 260                        }
 261
 262                        rcu_bh_qs(cpu);
 263                }
 264                h++;
 265                pending >>= 1;
 266        } while (pending);
 267
 268        local_irq_disable();
 269
 270        pending = local_softirq_pending();
 271        if (pending) {
 272                if (time_before(jiffies, end) && !need_resched() &&
 273                    --max_restart)
 274                        goto restart;
 275
 276                wakeup_softirqd();
 277        }
 278
 279        lockdep_softirq_exit();
 280
 281        account_irq_exit_time(current);
 282        __local_bh_enable(SOFTIRQ_OFFSET);
 283        tsk_restore_flags(current, old_flags, PF_MEMALLOC);
 284}
 285
 286#ifndef __ARCH_HAS_DO_SOFTIRQ
 287
 288asmlinkage void do_softirq(void)
 289{
 290        __u32 pending;
 291        unsigned long flags;
 292
 293        if (in_interrupt())
 294                return;
 295
 296        local_irq_save(flags);
 297
 298        pending = local_softirq_pending();
 299
 300        if (pending)
 301                __do_softirq();
 302
 303        local_irq_restore(flags);
 304}
 305
 306#endif
 307
 308/*
 309 * Enter an interrupt context.
 310 */
 311void irq_enter(void)
 312{
 313        int cpu = smp_processor_id();
 314
 315        rcu_irq_enter();
 316        if (is_idle_task(current) && !in_interrupt()) {
 317                /*
 318                 * Prevent raise_softirq from needlessly waking up ksoftirqd
 319                 * here, as softirq will be serviced on return from interrupt.
 320                 */
 321                local_bh_disable();
 322                tick_check_idle(cpu);
 323                _local_bh_enable();
 324        }
 325
 326        __irq_enter();
 327}
 328
 329static inline void invoke_softirq(void)
 330{
 331        if (!force_irqthreads) {
 332                /*
 333                 * We can safely execute softirq on the current stack if
 334                 * it is the irq stack, because it should be near empty
 335                 * at this stage. But we have no way to know if the arch
 336                 * calls irq_exit() on the irq stack. So call softirq
 337                 * in its own stack to prevent from any overrun on top
 338                 * of a potentially deep task stack.
 339                 */
 340                do_softirq();
 341        } else {
 342                wakeup_softirqd();
 343        }
 344}
 345
 346static inline void tick_irq_exit(void)
 347{
 348#ifdef CONFIG_NO_HZ_COMMON
 349        int cpu = smp_processor_id();
 350
 351        /* Make sure that timer wheel updates are propagated */
 352        if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 353                if (!in_interrupt())
 354                        tick_nohz_irq_exit();
 355        }
 356#endif
 357}
 358
 359/*
 360 * Exit an interrupt context. Process softirqs if needed and possible:
 361 */
 362void irq_exit(void)
 363{
 364#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 365        local_irq_disable();
 366#else
 367        WARN_ON_ONCE(!irqs_disabled());
 368#endif
 369
 370        account_irq_exit_time(current);
 371        trace_hardirq_exit();
 372        sub_preempt_count(HARDIRQ_OFFSET);
 373        if (!in_interrupt() && local_softirq_pending())
 374                invoke_softirq();
 375
 376        tick_irq_exit();
 377        rcu_irq_exit();
 378}
 379
 380/*
 381 * This function must run with irqs disabled!
 382 */
 383inline void raise_softirq_irqoff(unsigned int nr)
 384{
 385        __raise_softirq_irqoff(nr);
 386
 387        /*
 388         * If we're in an interrupt or softirq, we're done
 389         * (this also catches softirq-disabled code). We will
 390         * actually run the softirq once we return from
 391         * the irq or softirq.
 392         *
 393         * Otherwise we wake up ksoftirqd to make sure we
 394         * schedule the softirq soon.
 395         */
 396        if (!in_interrupt())
 397                wakeup_softirqd();
 398}
 399
 400void raise_softirq(unsigned int nr)
 401{
 402        unsigned long flags;
 403
 404        local_irq_save(flags);
 405        raise_softirq_irqoff(nr);
 406        local_irq_restore(flags);
 407}
 408
 409void __raise_softirq_irqoff(unsigned int nr)
 410{
 411        trace_softirq_raise(nr);
 412        or_softirq_pending(1UL << nr);
 413}
 414
 415void open_softirq(int nr, void (*action)(struct softirq_action *))
 416{
 417        softirq_vec[nr].action = action;
 418}
 419
 420/*
 421 * Tasklets
 422 */
 423struct tasklet_head
 424{
 425        struct tasklet_struct *head;
 426        struct tasklet_struct **tail;
 427};
 428
 429static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 430static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 431
 432void __tasklet_schedule(struct tasklet_struct *t)
 433{
 434        unsigned long flags;
 435
 436        local_irq_save(flags);
 437        t->next = NULL;
 438        *__this_cpu_read(tasklet_vec.tail) = t;
 439        __this_cpu_write(tasklet_vec.tail, &(t->next));
 440        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 441        local_irq_restore(flags);
 442}
 443
 444EXPORT_SYMBOL(__tasklet_schedule);
 445
 446void __tasklet_hi_schedule(struct tasklet_struct *t)
 447{
 448        unsigned long flags;
 449
 450        local_irq_save(flags);
 451        t->next = NULL;
 452        *__this_cpu_read(tasklet_hi_vec.tail) = t;
 453        __this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
 454        raise_softirq_irqoff(HI_SOFTIRQ);
 455        local_irq_restore(flags);
 456}
 457
 458EXPORT_SYMBOL(__tasklet_hi_schedule);
 459
 460void __tasklet_hi_schedule_first(struct tasklet_struct *t)
 461{
 462        BUG_ON(!irqs_disabled());
 463
 464        t->next = __this_cpu_read(tasklet_hi_vec.head);
 465        __this_cpu_write(tasklet_hi_vec.head, t);
 466        __raise_softirq_irqoff(HI_SOFTIRQ);
 467}
 468
 469EXPORT_SYMBOL(__tasklet_hi_schedule_first);
 470
 471static void tasklet_action(struct softirq_action *a)
 472{
 473        struct tasklet_struct *list;
 474
 475        local_irq_disable();
 476        list = __this_cpu_read(tasklet_vec.head);
 477        __this_cpu_write(tasklet_vec.head, NULL);
 478        __this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head);
 479        local_irq_enable();
 480
 481        while (list) {
 482                struct tasklet_struct *t = list;
 483
 484                list = list->next;
 485
 486                if (tasklet_trylock(t)) {
 487                        if (!atomic_read(&t->count)) {
 488                                if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 489                                        BUG();
 490                                t->func(t->data);
 491                                tasklet_unlock(t);
 492                                continue;
 493                        }
 494                        tasklet_unlock(t);
 495                }
 496
 497                local_irq_disable();
 498                t->next = NULL;
 499                *__this_cpu_read(tasklet_vec.tail) = t;
 500                __this_cpu_write(tasklet_vec.tail, &(t->next));
 501                __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 502                local_irq_enable();
 503        }
 504}
 505
 506static void tasklet_hi_action(struct softirq_action *a)
 507{
 508        struct tasklet_struct *list;
 509
 510        local_irq_disable();
 511        list = __this_cpu_read(tasklet_hi_vec.head);
 512        __this_cpu_write(tasklet_hi_vec.head, NULL);
 513        __this_cpu_write(tasklet_hi_vec.tail, &__get_cpu_var(tasklet_hi_vec).head);
 514        local_irq_enable();
 515
 516        while (list) {
 517                struct tasklet_struct *t = list;
 518
 519                list = list->next;
 520
 521                if (tasklet_trylock(t)) {
 522                        if (!atomic_read(&t->count)) {
 523                                if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 524                                        BUG();
 525                                t->func(t->data);
 526                                tasklet_unlock(t);
 527                                continue;
 528                        }
 529                        tasklet_unlock(t);
 530                }
 531
 532                local_irq_disable();
 533                t->next = NULL;
 534                *__this_cpu_read(tasklet_hi_vec.tail) = t;
 535                __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
 536                __raise_softirq_irqoff(HI_SOFTIRQ);
 537                local_irq_enable();
 538        }
 539}
 540
 541
 542void tasklet_init(struct tasklet_struct *t,
 543                  void (*func)(unsigned long), unsigned long data)
 544{
 545        t->next = NULL;
 546        t->state = 0;
 547        atomic_set(&t->count, 0);
 548        t->func = func;
 549        t->data = data;
 550}
 551
 552EXPORT_SYMBOL(tasklet_init);
 553
 554void tasklet_kill(struct tasklet_struct *t)
 555{
 556        if (in_interrupt())
 557                printk("Attempt to kill tasklet from interrupt\n");
 558
 559        while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 560                do {
 561                        yield();
 562                } while (test_bit(TASKLET_STATE_SCHED, &t->state));
 563        }
 564        tasklet_unlock_wait(t);
 565        clear_bit(TASKLET_STATE_SCHED, &t->state);
 566}
 567
 568EXPORT_SYMBOL(tasklet_kill);
 569
 570/*
 571 * tasklet_hrtimer
 572 */
 573
 574/*
 575 * The trampoline is called when the hrtimer expires. It schedules a tasklet
 576 * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
 577 * hrtimer callback, but from softirq context.
 578 */
 579static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
 580{
 581        struct tasklet_hrtimer *ttimer =
 582                container_of(timer, struct tasklet_hrtimer, timer);
 583
 584        tasklet_hi_schedule(&ttimer->tasklet);
 585        return HRTIMER_NORESTART;
 586}
 587
 588/*
 589 * Helper function which calls the hrtimer callback from
 590 * tasklet/softirq context
 591 */
 592static void __tasklet_hrtimer_trampoline(unsigned long data)
 593{
 594        struct tasklet_hrtimer *ttimer = (void *)data;
 595        enum hrtimer_restart restart;
 596
 597        restart = ttimer->function(&ttimer->timer);
 598        if (restart != HRTIMER_NORESTART)
 599                hrtimer_restart(&ttimer->timer);
 600}
 601
 602/**
 603 * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
 604 * @ttimer:      tasklet_hrtimer which is initialized
 605 * @function:    hrtimer callback function which gets called from softirq context
 606 * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
 607 * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
 608 */
 609void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
 610                          enum hrtimer_restart (*function)(struct hrtimer *),
 611                          clockid_t which_clock, enum hrtimer_mode mode)
 612{
 613        hrtimer_init(&ttimer->timer, which_clock, mode);
 614        ttimer->timer.function = __hrtimer_tasklet_trampoline;
 615        tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
 616                     (unsigned long)ttimer);
 617        ttimer->function = function;
 618}
 619EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
 620
 621/*
 622 * Remote softirq bits
 623 */
 624
 625DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
 626EXPORT_PER_CPU_SYMBOL(softirq_work_list);
 627
 628static void __local_trigger(struct call_single_data *cp, int softirq)
 629{
 630        struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
 631
 632        list_add_tail(&cp->list, head);
 633
 634        /* Trigger the softirq only if the list was previously empty.  */
 635        if (head->next == &cp->list)
 636                raise_softirq_irqoff(softirq);
 637}
 638
 639#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
 640static void remote_softirq_receive(void *data)
 641{
 642        struct call_single_data *cp = data;
 643        unsigned long flags;
 644        int softirq;
 645
 646        softirq = *(int *)cp->info;
 647        local_irq_save(flags);
 648        __local_trigger(cp, softirq);
 649        local_irq_restore(flags);
 650}
 651
 652static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 653{
 654        if (cpu_online(cpu)) {
 655                cp->func = remote_softirq_receive;
 656                cp->info = &softirq;
 657                cp->flags = 0;
 658
 659                __smp_call_function_single(cpu, cp, 0);
 660                return 0;
 661        }
 662        return 1;
 663}
 664#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
 665static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 666{
 667        return 1;
 668}
 669#endif
 670
 671/**
 672 * __send_remote_softirq - try to schedule softirq work on a remote cpu
 673 * @cp: private SMP call function data area
 674 * @cpu: the remote cpu
 675 * @this_cpu: the currently executing cpu
 676 * @softirq: the softirq for the work
 677 *
 678 * Attempt to schedule softirq work on a remote cpu.  If this cannot be
 679 * done, the work is instead queued up on the local cpu.
 680 *
 681 * Interrupts must be disabled.
 682 */
 683void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
 684{
 685        if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
 686                __local_trigger(cp, softirq);
 687}
 688EXPORT_SYMBOL(__send_remote_softirq);
 689
 690/**
 691 * send_remote_softirq - try to schedule softirq work on a remote cpu
 692 * @cp: private SMP call function data area
 693 * @cpu: the remote cpu
 694 * @softirq: the softirq for the work
 695 *
 696 * Like __send_remote_softirq except that disabling interrupts and
 697 * computing the current cpu is done for the caller.
 698 */
 699void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 700{
 701        unsigned long flags;
 702        int this_cpu;
 703
 704        local_irq_save(flags);
 705        this_cpu = smp_processor_id();
 706        __send_remote_softirq(cp, cpu, this_cpu, softirq);
 707        local_irq_restore(flags);
 708}
 709EXPORT_SYMBOL(send_remote_softirq);
 710
 711static int remote_softirq_cpu_notify(struct notifier_block *self,
 712                                               unsigned long action, void *hcpu)
 713{
 714        /*
 715         * If a CPU goes away, splice its entries to the current CPU
 716         * and trigger a run of the softirq
 717         */
 718        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
 719                int cpu = (unsigned long) hcpu;
 720                int i;
 721
 722                local_irq_disable();
 723                for (i = 0; i < NR_SOFTIRQS; i++) {
 724                        struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
 725                        struct list_head *local_head;
 726
 727                        if (list_empty(head))
 728                                continue;
 729
 730                        local_head = &__get_cpu_var(softirq_work_list[i]);
 731                        list_splice_init(head, local_head);
 732                        raise_softirq_irqoff(i);
 733                }
 734                local_irq_enable();
 735        }
 736
 737        return NOTIFY_OK;
 738}
 739
 740static struct notifier_block remote_softirq_cpu_notifier = {
 741        .notifier_call  = remote_softirq_cpu_notify,
 742};
 743
 744void __init softirq_init(void)
 745{
 746        int cpu;
 747
 748        for_each_possible_cpu(cpu) {
 749                int i;
 750
 751                per_cpu(tasklet_vec, cpu).tail =
 752                        &per_cpu(tasklet_vec, cpu).head;
 753                per_cpu(tasklet_hi_vec, cpu).tail =
 754                        &per_cpu(tasklet_hi_vec, cpu).head;
 755                for (i = 0; i < NR_SOFTIRQS; i++)
 756                        INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
 757        }
 758
 759        register_hotcpu_notifier(&remote_softirq_cpu_notifier);
 760
 761        open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 762        open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 763}
 764
 765static int ksoftirqd_should_run(unsigned int cpu)
 766{
 767        return local_softirq_pending();
 768}
 769
 770static void run_ksoftirqd(unsigned int cpu)
 771{
 772        local_irq_disable();
 773        if (local_softirq_pending()) {
 774                __do_softirq();
 775                rcu_note_context_switch(cpu);
 776                local_irq_enable();
 777                cond_resched();
 778                return;
 779        }
 780        local_irq_enable();
 781}
 782
 783#ifdef CONFIG_HOTPLUG_CPU
 784/*
 785 * tasklet_kill_immediate is called to remove a tasklet which can already be
 786 * scheduled for execution on @cpu.
 787 *
 788 * Unlike tasklet_kill, this function removes the tasklet
 789 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 790 *
 791 * When this function is called, @cpu must be in the CPU_DEAD state.
 792 */
 793void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 794{
 795        struct tasklet_struct **i;
 796
 797        BUG_ON(cpu_online(cpu));
 798        BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 799
 800        if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 801                return;
 802
 803        /* CPU is dead, so no lock needed. */
 804        for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 805                if (*i == t) {
 806                        *i = t->next;
 807                        /* If this was the tail element, move the tail ptr */
 808                        if (*i == NULL)
 809                                per_cpu(tasklet_vec, cpu).tail = i;
 810                        return;
 811                }
 812        }
 813        BUG();
 814}
 815
 816static void takeover_tasklets(unsigned int cpu)
 817{
 818        /* CPU is dead, so no lock needed. */
 819        local_irq_disable();
 820
 821        /* Find end, append list for that CPU. */
 822        if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 823                *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 824                this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 825                per_cpu(tasklet_vec, cpu).head = NULL;
 826                per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 827        }
 828        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 829
 830        if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 831                *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 832                __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 833                per_cpu(tasklet_hi_vec, cpu).head = NULL;
 834                per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 835        }
 836        raise_softirq_irqoff(HI_SOFTIRQ);
 837
 838        local_irq_enable();
 839}
 840#endif /* CONFIG_HOTPLUG_CPU */
 841
 842static int cpu_callback(struct notifier_block *nfb,
 843                                  unsigned long action,
 844                                  void *hcpu)
 845{
 846        switch (action) {
 847#ifdef CONFIG_HOTPLUG_CPU
 848        case CPU_DEAD:
 849        case CPU_DEAD_FROZEN:
 850                takeover_tasklets((unsigned long)hcpu);
 851                break;
 852#endif /* CONFIG_HOTPLUG_CPU */
 853        }
 854        return NOTIFY_OK;
 855}
 856
 857static struct notifier_block cpu_nfb = {
 858        .notifier_call = cpu_callback
 859};
 860
 861static struct smp_hotplug_thread softirq_threads = {
 862        .store                  = &ksoftirqd,
 863        .thread_should_run      = ksoftirqd_should_run,
 864        .thread_fn              = run_ksoftirqd,
 865        .thread_comm            = "ksoftirqd/%u",
 866};
 867
 868static __init int spawn_ksoftirqd(void)
 869{
 870        register_cpu_notifier(&cpu_nfb);
 871
 872        BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 873
 874        return 0;
 875}
 876early_initcall(spawn_ksoftirqd);
 877
 878/*
 879 * [ These __weak aliases are kept in a separate compilation unit, so that
 880 *   GCC does not inline them incorrectly. ]
 881 */
 882
 883int __init __weak early_irq_init(void)
 884{
 885        return 0;
 886}
 887
 888int __init __weak arch_probe_nr_irqs(void)
 889{
 890        return NR_IRQS_LEGACY;
 891}
 892
 893int __init __weak arch_early_irq_init(void)
 894{
 895        return 0;
 896}
 897
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