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
  11#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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#include <linux/irq.h>
  29
  30#define CREATE_TRACE_POINTS
  31#include <trace/events/irq.h>
  32
  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
  60const char * const 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
  95void __local_bh_disable_ip(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 preempt_count_add 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_add(cnt);
 110        /*
 111         * Were softirqs turned off above:
 112         */
 113        if (softirq_count() == (cnt & SOFTIRQ_MASK))
 114                trace_softirqs_off(ip);
 115        raw_local_irq_restore(flags);
 116
 117        if (preempt_count() == cnt) {
 118#ifdef CONFIG_DEBUG_PREEMPT
 119                current->preempt_disable_ip = get_parent_ip(CALLER_ADDR1);
 120#endif
 121                trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
 122        }
 123}
 124EXPORT_SYMBOL(__local_bh_disable_ip);
 125#endif /* CONFIG_TRACE_IRQFLAGS */
 126
 127static void __local_bh_enable(unsigned int cnt)
 128{
 129        WARN_ON_ONCE(!irqs_disabled());
 130
 131        if (softirq_count() == (cnt & SOFTIRQ_MASK))
 132                trace_softirqs_on(_RET_IP_);
 133        preempt_count_sub(cnt);
 134}
 135
 136/*
 137 * Special-case - softirqs can safely be enabled in
 138 * cond_resched_softirq(), or by __do_softirq(),
 139 * without processing still-pending softirqs:
 140 */
 141void _local_bh_enable(void)
 142{
 143        WARN_ON_ONCE(in_irq());
 144        __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 145}
 146EXPORT_SYMBOL(_local_bh_enable);
 147
 148void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 149{
 150        WARN_ON_ONCE(in_irq() || irqs_disabled());
 151#ifdef CONFIG_TRACE_IRQFLAGS
 152        local_irq_disable();
 153#endif
 154        /*
 155         * Are softirqs going to be turned on now:
 156         */
 157        if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 158                trace_softirqs_on(ip);
 159        /*
 160         * Keep preemption disabled until we are done with
 161         * softirq processing:
 162         */
 163        preempt_count_sub(cnt - 1);
 164
 165        if (unlikely(!in_interrupt() && local_softirq_pending())) {
 166                /*
 167                 * Run softirq if any pending. And do it in its own stack
 168                 * as we may be calling this deep in a task call stack already.
 169                 */
 170                do_softirq();
 171        }
 172
 173        preempt_count_dec();
 174#ifdef CONFIG_TRACE_IRQFLAGS
 175        local_irq_enable();
 176#endif
 177        preempt_check_resched();
 178}
 179EXPORT_SYMBOL(__local_bh_enable_ip);
 180
 181/*
 182 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 183 * but break the loop if need_resched() is set or after 2 ms.
 184 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 185 * certain cases, such as stop_machine(), jiffies may cease to
 186 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 187 * well to make sure we eventually return from this method.
 188 *
 189 * These limits have been established via experimentation.
 190 * The two things to balance is latency against fairness -
 191 * we want to handle softirqs as soon as possible, but they
 192 * should not be able to lock up the box.
 193 */
 194#define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 195#define MAX_SOFTIRQ_RESTART 10
 196
 197#ifdef CONFIG_TRACE_IRQFLAGS
 198/*
 199 * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 200 * to keep the lockdep irq context tracking as tight as possible in order to
 201 * not miss-qualify lock contexts and miss possible deadlocks.
 202 */
 203
 204static inline bool lockdep_softirq_start(void)
 205{
 206        bool in_hardirq = false;
 207
 208        if (trace_hardirq_context(current)) {
 209                in_hardirq = true;
 210                trace_hardirq_exit();
 211        }
 212
 213        lockdep_softirq_enter();
 214
 215        return in_hardirq;
 216}
 217
 218static inline void lockdep_softirq_end(bool in_hardirq)
 219{
 220        lockdep_softirq_exit();
 221
 222        if (in_hardirq)
 223                trace_hardirq_enter();
 224}
 225#else
 226static inline bool lockdep_softirq_start(void) { return false; }
 227static inline void lockdep_softirq_end(bool in_hardirq) { }
 228#endif
 229
 230asmlinkage __visible void __do_softirq(void)
 231{
 232        unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 233        unsigned long old_flags = current->flags;
 234        int max_restart = MAX_SOFTIRQ_RESTART;
 235        struct softirq_action *h;
 236        bool in_hardirq;
 237        __u32 pending;
 238        int softirq_bit;
 239
 240        /*
 241         * Mask out PF_MEMALLOC s current task context is borrowed for the
 242         * softirq. A softirq handled such as network RX might set PF_MEMALLOC
 243         * again if the socket is related to swap
 244         */
 245        current->flags &= ~PF_MEMALLOC;
 246
 247        pending = local_softirq_pending();
 248        account_irq_enter_time(current);
 249
 250        __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 251        in_hardirq = lockdep_softirq_start();
 252
 253restart:
 254        /* Reset the pending bitmask before enabling irqs */
 255        set_softirq_pending(0);
 256
 257        local_irq_enable();
 258
 259        h = softirq_vec;
 260
 261        while ((softirq_bit = ffs(pending))) {
 262                unsigned int vec_nr;
 263                int prev_count;
 264
 265                h += softirq_bit - 1;
 266
 267                vec_nr = h - softirq_vec;
 268                prev_count = preempt_count();
 269
 270                kstat_incr_softirqs_this_cpu(vec_nr);
 271
 272                trace_softirq_entry(vec_nr);
 273                h->action(h);
 274                trace_softirq_exit(vec_nr);
 275                if (unlikely(prev_count != preempt_count())) {
 276                        pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 277                               vec_nr, softirq_to_name[vec_nr], h->action,
 278                               prev_count, preempt_count());
 279                        preempt_count_set(prev_count);
 280                }
 281                h++;
 282                pending >>= softirq_bit;
 283        }
 284
 285        rcu_bh_qs();
 286        local_irq_disable();
 287
 288        pending = local_softirq_pending();
 289        if (pending) {
 290                if (time_before(jiffies, end) && !need_resched() &&
 291                    --max_restart)
 292                        goto restart;
 293
 294                wakeup_softirqd();
 295        }
 296
 297        lockdep_softirq_end(in_hardirq);
 298        account_irq_exit_time(current);
 299        __local_bh_enable(SOFTIRQ_OFFSET);
 300        WARN_ON_ONCE(in_interrupt());
 301        tsk_restore_flags(current, old_flags, PF_MEMALLOC);
 302}
 303
 304asmlinkage __visible void do_softirq(void)
 305{
 306        __u32 pending;
 307        unsigned long flags;
 308
 309        if (in_interrupt())
 310                return;
 311
 312        local_irq_save(flags);
 313
 314        pending = local_softirq_pending();
 315
 316        if (pending)
 317                do_softirq_own_stack();
 318
 319        local_irq_restore(flags);
 320}
 321
 322/*
 323 * Enter an interrupt context.
 324 */
 325void irq_enter(void)
 326{
 327        rcu_irq_enter();
 328        if (is_idle_task(current) && !in_interrupt()) {
 329                /*
 330                 * Prevent raise_softirq from needlessly waking up ksoftirqd
 331                 * here, as softirq will be serviced on return from interrupt.
 332                 */
 333                local_bh_disable();
 334                tick_irq_enter();
 335                _local_bh_enable();
 336        }
 337
 338        __irq_enter();
 339}
 340
 341static inline void invoke_softirq(void)
 342{
 343        if (!force_irqthreads) {
 344#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 345                /*
 346                 * We can safely execute softirq on the current stack if
 347                 * it is the irq stack, because it should be near empty
 348                 * at this stage.
 349                 */
 350                __do_softirq();
 351#else
 352                /*
 353                 * Otherwise, irq_exit() is called on the task stack that can
 354                 * be potentially deep already. So call softirq in its own stack
 355                 * to prevent from any overrun.
 356                 */
 357                do_softirq_own_stack();
 358#endif
 359        } else {
 360                wakeup_softirqd();
 361        }
 362}
 363
 364static inline void tick_irq_exit(void)
 365{
 366#ifdef CONFIG_NO_HZ_COMMON
 367        int cpu = smp_processor_id();
 368
 369        /* Make sure that timer wheel updates are propagated */
 370        if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 371                if (!in_interrupt())
 372                        tick_nohz_irq_exit();
 373        }
 374#endif
 375}
 376
 377/*
 378 * Exit an interrupt context. Process softirqs if needed and possible:
 379 */
 380void irq_exit(void)
 381{
 382#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 383        local_irq_disable();
 384#else
 385        WARN_ON_ONCE(!irqs_disabled());
 386#endif
 387
 388        account_irq_exit_time(current);
 389        preempt_count_sub(HARDIRQ_OFFSET);
 390        if (!in_interrupt() && local_softirq_pending())
 391                invoke_softirq();
 392
 393        tick_irq_exit();
 394        rcu_irq_exit();
 395        trace_hardirq_exit(); /* must be last! */
 396}
 397
 398/*
 399 * This function must run with irqs disabled!
 400 */
 401inline void raise_softirq_irqoff(unsigned int nr)
 402{
 403        __raise_softirq_irqoff(nr);
 404
 405        /*
 406         * If we're in an interrupt or softirq, we're done
 407         * (this also catches softirq-disabled code). We will
 408         * actually run the softirq once we return from
 409         * the irq or softirq.
 410         *
 411         * Otherwise we wake up ksoftirqd to make sure we
 412         * schedule the softirq soon.
 413         */
 414        if (!in_interrupt())
 415                wakeup_softirqd();
 416}
 417
 418void raise_softirq(unsigned int nr)
 419{
 420        unsigned long flags;
 421
 422        local_irq_save(flags);
 423        raise_softirq_irqoff(nr);
 424        local_irq_restore(flags);
 425}
 426
 427void __raise_softirq_irqoff(unsigned int nr)
 428{
 429        trace_softirq_raise(nr);
 430        or_softirq_pending(1UL << nr);
 431}
 432
 433void open_softirq(int nr, void (*action)(struct softirq_action *))
 434{
 435        softirq_vec[nr].action = action;
 436}
 437
 438/*
 439 * Tasklets
 440 */
 441struct tasklet_head {
 442        struct tasklet_struct *head;
 443        struct tasklet_struct **tail;
 444};
 445
 446static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 447static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 448
 449void __tasklet_schedule(struct tasklet_struct *t)
 450{
 451        unsigned long flags;
 452
 453        local_irq_save(flags);
 454        t->next = NULL;
 455        *__this_cpu_read(tasklet_vec.tail) = t;
 456        __this_cpu_write(tasklet_vec.tail, &(t->next));
 457        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 458        local_irq_restore(flags);
 459}
 460EXPORT_SYMBOL(__tasklet_schedule);
 461
 462void __tasklet_hi_schedule(struct tasklet_struct *t)
 463{
 464        unsigned long flags;
 465
 466        local_irq_save(flags);
 467        t->next = NULL;
 468        *__this_cpu_read(tasklet_hi_vec.tail) = t;
 469        __this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
 470        raise_softirq_irqoff(HI_SOFTIRQ);
 471        local_irq_restore(flags);
 472}
 473EXPORT_SYMBOL(__tasklet_hi_schedule);
 474
 475void __tasklet_hi_schedule_first(struct tasklet_struct *t)
 476{
 477        BUG_ON(!irqs_disabled());
 478
 479        t->next = __this_cpu_read(tasklet_hi_vec.head);
 480        __this_cpu_write(tasklet_hi_vec.head, t);
 481        __raise_softirq_irqoff(HI_SOFTIRQ);
 482}
 483EXPORT_SYMBOL(__tasklet_hi_schedule_first);
 484
 485static void tasklet_action(struct softirq_action *a)
 486{
 487        struct tasklet_struct *list;
 488
 489        local_irq_disable();
 490        list = __this_cpu_read(tasklet_vec.head);
 491        __this_cpu_write(tasklet_vec.head, NULL);
 492        __this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
 493        local_irq_enable();
 494
 495        while (list) {
 496                struct tasklet_struct *t = list;
 497
 498                list = list->next;
 499
 500                if (tasklet_trylock(t)) {
 501                        if (!atomic_read(&t->count)) {
 502                                if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 503                                                        &t->state))
 504                                        BUG();
 505                                t->func(t->data);
 506                                tasklet_unlock(t);
 507                                continue;
 508                        }
 509                        tasklet_unlock(t);
 510                }
 511
 512                local_irq_disable();
 513                t->next = NULL;
 514                *__this_cpu_read(tasklet_vec.tail) = t;
 515                __this_cpu_write(tasklet_vec.tail, &(t->next));
 516                __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 517                local_irq_enable();
 518        }
 519}
 520
 521static void tasklet_hi_action(struct softirq_action *a)
 522{
 523        struct tasklet_struct *list;
 524
 525        local_irq_disable();
 526        list = __this_cpu_read(tasklet_hi_vec.head);
 527        __this_cpu_write(tasklet_hi_vec.head, NULL);
 528        __this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
 529        local_irq_enable();
 530
 531        while (list) {
 532                struct tasklet_struct *t = list;
 533
 534                list = list->next;
 535
 536                if (tasklet_trylock(t)) {
 537                        if (!atomic_read(&t->count)) {
 538                                if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 539                                                        &t->state))
 540                                        BUG();
 541                                t->func(t->data);
 542                                tasklet_unlock(t);
 543                                continue;
 544                        }
 545                        tasklet_unlock(t);
 546                }
 547
 548                local_irq_disable();
 549                t->next = NULL;
 550                *__this_cpu_read(tasklet_hi_vec.tail) = t;
 551                __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
 552                __raise_softirq_irqoff(HI_SOFTIRQ);
 553                local_irq_enable();
 554        }
 555}
 556
 557void tasklet_init(struct tasklet_struct *t,
 558                  void (*func)(unsigned long), unsigned long data)
 559{
 560        t->next = NULL;
 561        t->state = 0;
 562        atomic_set(&t->count, 0);
 563        t->func = func;
 564        t->data = data;
 565}
 566EXPORT_SYMBOL(tasklet_init);
 567
 568void tasklet_kill(struct tasklet_struct *t)
 569{
 570        if (in_interrupt())
 571                pr_notice("Attempt to kill tasklet from interrupt\n");
 572
 573        while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 574                do {
 575                        yield();
 576                } while (test_bit(TASKLET_STATE_SCHED, &t->state));
 577        }
 578        tasklet_unlock_wait(t);
 579        clear_bit(TASKLET_STATE_SCHED, &t->state);
 580}
 581EXPORT_SYMBOL(tasklet_kill);
 582
 583/*
 584 * tasklet_hrtimer
 585 */
 586
 587/*
 588 * The trampoline is called when the hrtimer expires. It schedules a tasklet
 589 * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
 590 * hrtimer callback, but from softirq context.
 591 */
 592static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
 593{
 594        struct tasklet_hrtimer *ttimer =
 595                container_of(timer, struct tasklet_hrtimer, timer);
 596
 597        tasklet_hi_schedule(&ttimer->tasklet);
 598        return HRTIMER_NORESTART;
 599}
 600
 601/*
 602 * Helper function which calls the hrtimer callback from
 603 * tasklet/softirq context
 604 */
 605static void __tasklet_hrtimer_trampoline(unsigned long data)
 606{
 607        struct tasklet_hrtimer *ttimer = (void *)data;
 608        enum hrtimer_restart restart;
 609
 610        restart = ttimer->function(&ttimer->timer);
 611        if (restart != HRTIMER_NORESTART)
 612                hrtimer_restart(&ttimer->timer);
 613}
 614
 615/**
 616 * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
 617 * @ttimer:      tasklet_hrtimer which is initialized
 618 * @function:    hrtimer callback function which gets called from softirq context
 619 * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
 620 * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
 621 */
 622void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
 623                          enum hrtimer_restart (*function)(struct hrtimer *),
 624                          clockid_t which_clock, enum hrtimer_mode mode)
 625{
 626        hrtimer_init(&ttimer->timer, which_clock, mode);
 627        ttimer->timer.function = __hrtimer_tasklet_trampoline;
 628        tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
 629                     (unsigned long)ttimer);
 630        ttimer->function = function;
 631}
 632EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
 633
 634void __init softirq_init(void)
 635{
 636        int cpu;
 637
 638        for_each_possible_cpu(cpu) {
 639                per_cpu(tasklet_vec, cpu).tail =
 640                        &per_cpu(tasklet_vec, cpu).head;
 641                per_cpu(tasklet_hi_vec, cpu).tail =
 642                        &per_cpu(tasklet_hi_vec, cpu).head;
 643        }
 644
 645        open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 646        open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 647}
 648
 649static int ksoftirqd_should_run(unsigned int cpu)
 650{
 651        return local_softirq_pending();
 652}
 653
 654static void run_ksoftirqd(unsigned int cpu)
 655{
 656        local_irq_disable();
 657        if (local_softirq_pending()) {
 658                /*
 659                 * We can safely run softirq on inline stack, as we are not deep
 660                 * in the task stack here.
 661                 */
 662                __do_softirq();
 663                local_irq_enable();
 664                cond_resched_rcu_qs();
 665                return;
 666        }
 667        local_irq_enable();
 668}
 669
 670#ifdef CONFIG_HOTPLUG_CPU
 671/*
 672 * tasklet_kill_immediate is called to remove a tasklet which can already be
 673 * scheduled for execution on @cpu.
 674 *
 675 * Unlike tasklet_kill, this function removes the tasklet
 676 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 677 *
 678 * When this function is called, @cpu must be in the CPU_DEAD state.
 679 */
 680void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 681{
 682        struct tasklet_struct **i;
 683
 684        BUG_ON(cpu_online(cpu));
 685        BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 686
 687        if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 688                return;
 689
 690        /* CPU is dead, so no lock needed. */
 691        for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 692                if (*i == t) {
 693                        *i = t->next;
 694                        /* If this was the tail element, move the tail ptr */
 695                        if (*i == NULL)
 696                                per_cpu(tasklet_vec, cpu).tail = i;
 697                        return;
 698                }
 699        }
 700        BUG();
 701}
 702
 703static void takeover_tasklets(unsigned int cpu)
 704{
 705        /* CPU is dead, so no lock needed. */
 706        local_irq_disable();
 707
 708        /* Find end, append list for that CPU. */
 709        if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 710                *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 711                this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 712                per_cpu(tasklet_vec, cpu).head = NULL;
 713                per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 714        }
 715        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 716
 717        if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 718                *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 719                __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 720                per_cpu(tasklet_hi_vec, cpu).head = NULL;
 721                per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 722        }
 723        raise_softirq_irqoff(HI_SOFTIRQ);
 724
 725        local_irq_enable();
 726}
 727#endif /* CONFIG_HOTPLUG_CPU */
 728
 729static int cpu_callback(struct notifier_block *nfb, unsigned long action,
 730                        void *hcpu)
 731{
 732        switch (action) {
 733#ifdef CONFIG_HOTPLUG_CPU
 734        case CPU_DEAD:
 735        case CPU_DEAD_FROZEN:
 736                takeover_tasklets((unsigned long)hcpu);
 737                break;
 738#endif /* CONFIG_HOTPLUG_CPU */
 739        }
 740        return NOTIFY_OK;
 741}
 742
 743static struct notifier_block cpu_nfb = {
 744        .notifier_call = cpu_callback
 745};
 746
 747static struct smp_hotplug_thread softirq_threads = {
 748        .store                  = &ksoftirqd,
 749        .thread_should_run      = ksoftirqd_should_run,
 750        .thread_fn              = run_ksoftirqd,
 751        .thread_comm            = "ksoftirqd/%u",
 752};
 753
 754static __init int spawn_ksoftirqd(void)
 755{
 756        register_cpu_notifier(&cpu_nfb);
 757
 758        BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 759
 760        return 0;
 761}
 762early_initcall(spawn_ksoftirqd);
 763
 764/*
 765 * [ These __weak aliases are kept in a separate compilation unit, so that
 766 *   GCC does not inline them incorrectly. ]
 767 */
 768
 769int __init __weak early_irq_init(void)
 770{
 771        return 0;
 772}
 773
 774int __init __weak arch_probe_nr_irqs(void)
 775{
 776        return NR_IRQS_LEGACY;
 777}
 778
 779int __init __weak arch_early_irq_init(void)
 780{
 781        return 0;
 782}
 783
 784unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 785{
 786        return from;
 787}
 788