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/tick.h>
  27
  28#define CREATE_TRACE_POINTS
  29#include <trace/events/irq.h>
  30
  31#include <asm/irq.h>
  32/*
  33   - No shared variables, all the data are CPU local.
  34   - If a softirq needs serialization, let it serialize itself
  35     by its own spinlocks.
  36   - Even if softirq is serialized, only local cpu is marked for
  37     execution. Hence, we get something sort of weak cpu binding.
  38     Though it is still not clear, will it result in better locality
  39     or will not.
  40
  41   Examples:
  42   - NET RX softirq. It is multithreaded and does not require
  43     any global serialization.
  44   - NET TX softirq. It kicks software netdevice queues, hence
  45     it is logically serialized per device, but this serialization
  46     is invisible to common code.
  47   - Tasklets: serialized wrt itself.
  48 */
  49
  50#ifndef __ARCH_IRQ_STAT
  51irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
  52EXPORT_SYMBOL(irq_stat);
  53#endif
  54
  55static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
  56
  57DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  58
  59char *softirq_to_name[NR_SOFTIRQS] = {
  60        "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
  61        "TASKLET", "SCHED", "HRTIMER", "RCU"
  62};
  63
  64/*
  65 * we cannot loop indefinitely here to avoid userspace starvation,
  66 * but we also don't want to introduce a worst case 1/HZ latency
  67 * to the pending events, so lets the scheduler to balance
  68 * the softirq load for us.
  69 */
  70static void wakeup_softirqd(void)
  71{
  72        /* Interrupts are disabled: no need to stop preemption */
  73        struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  74
  75        if (tsk && tsk->state != TASK_RUNNING)
  76                wake_up_process(tsk);
  77}
  78
  79/*
  80 * preempt_count and SOFTIRQ_OFFSET usage:
  81 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
  82 *   softirq processing.
  83 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
  84 *   on local_bh_disable or local_bh_enable.
  85 * This lets us distinguish between whether we are currently processing
  86 * softirq and whether we just have bh disabled.
  87 */
  88
  89/*
  90 * This one is for softirq.c-internal use,
  91 * where hardirqs are disabled legitimately:
  92 */
  93#ifdef CONFIG_TRACE_IRQFLAGS
  94static void __local_bh_disable(unsigned long ip, unsigned int cnt)
  95{
  96        unsigned long flags;
  97
  98        WARN_ON_ONCE(in_irq());
  99
 100        raw_local_irq_save(flags);
 101        /*
 102         * The preempt tracer hooks into add_preempt_count and will break
 103         * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 104         * is set and before current->softirq_enabled is cleared.
 105         * We must manually increment preempt_count here and manually
 106         * call the trace_preempt_off later.
 107         */
 108        preempt_count() += cnt;
 109        /*
 110         * Were softirqs turned off above:
 111         */
 112        if (softirq_count() == cnt)
 113                trace_softirqs_off(ip);
 114        raw_local_irq_restore(flags);
 115
 116        if (preempt_count() == cnt)
 117                trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
 118}
 119#else /* !CONFIG_TRACE_IRQFLAGS */
 120static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
 121{
 122        add_preempt_count(cnt);
 123        barrier();
 124}
 125#endif /* CONFIG_TRACE_IRQFLAGS */
 126
 127void local_bh_disable(void)
 128{
 129        __local_bh_disable((unsigned long)__builtin_return_address(0),
 130                                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((unsigned long)__builtin_return_address(0));
 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((unsigned long)__builtin_return_address(0));
 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 MAX_SOFTIRQ_RESTART times,
 198 * and we fall back to softirqd after that.
 199 *
 200 * This number has been established via experimentation.
 201 * The two things to balance is latency against fairness -
 202 * we want to handle softirqs as soon as possible, but they
 203 * should not be able to lock up the box.
 204 */
 205#define MAX_SOFTIRQ_RESTART 10
 206
 207asmlinkage void __do_softirq(void)
 208{
 209        struct softirq_action *h;
 210        __u32 pending;
 211        int max_restart = MAX_SOFTIRQ_RESTART;
 212        int cpu;
 213        unsigned long old_flags = current->flags;
 214
 215        /*
 216         * Mask out PF_MEMALLOC s current task context is borrowed for the
 217         * softirq. A softirq handled such as network RX might set PF_MEMALLOC
 218         * again if the socket is related to swap
 219         */
 220        current->flags &= ~PF_MEMALLOC;
 221
 222        pending = local_softirq_pending();
 223        account_system_vtime(current);
 224
 225        __local_bh_disable((unsigned long)__builtin_return_address(0),
 226                                SOFTIRQ_OFFSET);
 227        lockdep_softirq_enter();
 228
 229        cpu = smp_processor_id();
 230restart:
 231        /* Reset the pending bitmask before enabling irqs */
 232        set_softirq_pending(0);
 233
 234        local_irq_enable();
 235
 236        h = softirq_vec;
 237
 238        do {
 239                if (pending & 1) {
 240                        unsigned int vec_nr = h - softirq_vec;
 241                        int prev_count = preempt_count();
 242
 243                        kstat_incr_softirqs_this_cpu(vec_nr);
 244
 245                        trace_softirq_entry(vec_nr);
 246                        h->action(h);
 247                        trace_softirq_exit(vec_nr);
 248                        if (unlikely(prev_count != preempt_count())) {
 249                                printk(KERN_ERR "huh, entered softirq %u %s %p"
 250                                       "with preempt_count %08x,"
 251                                       " exited with %08x?\n", vec_nr,
 252                                       softirq_to_name[vec_nr], h->action,
 253                                       prev_count, preempt_count());
 254                                preempt_count() = prev_count;
 255                        }
 256
 257                        rcu_bh_qs(cpu);
 258                }
 259                h++;
 260                pending >>= 1;
 261        } while (pending);
 262
 263        local_irq_disable();
 264
 265        pending = local_softirq_pending();
 266        if (pending && --max_restart)
 267                goto restart;
 268
 269        if (pending)
 270                wakeup_softirqd();
 271
 272        lockdep_softirq_exit();
 273
 274        account_system_vtime(current);
 275        __local_bh_enable(SOFTIRQ_OFFSET);
 276        tsk_restore_flags(current, old_flags, PF_MEMALLOC);
 277}
 278
 279#ifndef __ARCH_HAS_DO_SOFTIRQ
 280
 281asmlinkage void do_softirq(void)
 282{
 283        __u32 pending;
 284        unsigned long flags;
 285
 286        if (in_interrupt())
 287                return;
 288
 289        local_irq_save(flags);
 290
 291        pending = local_softirq_pending();
 292
 293        if (pending)
 294                __do_softirq();
 295
 296        local_irq_restore(flags);
 297}
 298
 299#endif
 300
 301/*
 302 * Enter an interrupt context.
 303 */
 304void irq_enter(void)
 305{
 306        int cpu = smp_processor_id();
 307
 308        rcu_irq_enter();
 309        if (is_idle_task(current) && !in_interrupt()) {
 310                /*
 311                 * Prevent raise_softirq from needlessly waking up ksoftirqd
 312                 * here, as softirq will be serviced on return from interrupt.
 313                 */
 314                local_bh_disable();
 315                tick_check_idle(cpu);
 316                _local_bh_enable();
 317        }
 318
 319        __irq_enter();
 320}
 321
 322static inline void invoke_softirq(void)
 323{
 324        if (!force_irqthreads) {
 325#ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
 326                __do_softirq();
 327#else
 328                do_softirq();
 329#endif
 330        } else {
 331                __local_bh_disable((unsigned long)__builtin_return_address(0),
 332                                SOFTIRQ_OFFSET);
 333                wakeup_softirqd();
 334                __local_bh_enable(SOFTIRQ_OFFSET);
 335        }
 336}
 337
 338/*
 339 * Exit an interrupt context. Process softirqs if needed and possible:
 340 */
 341void irq_exit(void)
 342{
 343        account_system_vtime(current);
 344        trace_hardirq_exit();
 345        sub_preempt_count(IRQ_EXIT_OFFSET);
 346        if (!in_interrupt() && local_softirq_pending())
 347                invoke_softirq();
 348
 349#ifdef CONFIG_NO_HZ
 350        /* Make sure that timer wheel updates are propagated */
 351        if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched())
 352                tick_nohz_irq_exit();
 353#endif
 354        rcu_irq_exit();
 355        sched_preempt_enable_no_resched();
 356}
 357
 358/*
 359 * This function must run with irqs disabled!
 360 */
 361inline void raise_softirq_irqoff(unsigned int nr)
 362{
 363        __raise_softirq_irqoff(nr);
 364
 365        /*
 366         * If we're in an interrupt or softirq, we're done
 367         * (this also catches softirq-disabled code). We will
 368         * actually run the softirq once we return from
 369         * the irq or softirq.
 370         *
 371         * Otherwise we wake up ksoftirqd to make sure we
 372         * schedule the softirq soon.
 373         */
 374        if (!in_interrupt())
 375                wakeup_softirqd();
 376}
 377
 378void raise_softirq(unsigned int nr)
 379{
 380        unsigned long flags;
 381
 382        local_irq_save(flags);
 383        raise_softirq_irqoff(nr);
 384        local_irq_restore(flags);
 385}
 386
 387void __raise_softirq_irqoff(unsigned int nr)
 388{
 389        trace_softirq_raise(nr);
 390        or_softirq_pending(1UL << nr);
 391}
 392
 393void open_softirq(int nr, void (*action)(struct softirq_action *))
 394{
 395        softirq_vec[nr].action = action;
 396}
 397
 398/*
 399 * Tasklets
 400 */
 401struct tasklet_head
 402{
 403        struct tasklet_struct *head;
 404        struct tasklet_struct **tail;
 405};
 406
 407static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 408static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 409
 410void __tasklet_schedule(struct tasklet_struct *t)
 411{
 412        unsigned long flags;
 413
 414        local_irq_save(flags);
 415        t->next = NULL;
 416        *__this_cpu_read(tasklet_vec.tail) = t;
 417        __this_cpu_write(tasklet_vec.tail, &(t->next));
 418        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 419        local_irq_restore(flags);
 420}
 421
 422EXPORT_SYMBOL(__tasklet_schedule);
 423
 424void __tasklet_hi_schedule(struct tasklet_struct *t)
 425{
 426        unsigned long flags;
 427
 428        local_irq_save(flags);
 429        t->next = NULL;
 430        *__this_cpu_read(tasklet_hi_vec.tail) = t;
 431        __this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
 432        raise_softirq_irqoff(HI_SOFTIRQ);
 433        local_irq_restore(flags);
 434}
 435
 436EXPORT_SYMBOL(__tasklet_hi_schedule);
 437
 438void __tasklet_hi_schedule_first(struct tasklet_struct *t)
 439{
 440        BUG_ON(!irqs_disabled());
 441
 442        t->next = __this_cpu_read(tasklet_hi_vec.head);
 443        __this_cpu_write(tasklet_hi_vec.head, t);
 444        __raise_softirq_irqoff(HI_SOFTIRQ);
 445}
 446
 447EXPORT_SYMBOL(__tasklet_hi_schedule_first);
 448
 449static void tasklet_action(struct softirq_action *a)
 450{
 451        struct tasklet_struct *list;
 452
 453        local_irq_disable();
 454        list = __this_cpu_read(tasklet_vec.head);
 455        __this_cpu_write(tasklet_vec.head, NULL);
 456        __this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head);
 457        local_irq_enable();
 458
 459        while (list) {
 460                struct tasklet_struct *t = list;
 461
 462                list = list->next;
 463
 464                if (tasklet_trylock(t)) {
 465                        if (!atomic_read(&t->count)) {
 466                                if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 467                                        BUG();
 468                                t->func(t->data);
 469                                tasklet_unlock(t);
 470                                continue;
 471                        }
 472                        tasklet_unlock(t);
 473                }
 474
 475                local_irq_disable();
 476                t->next = NULL;
 477                *__this_cpu_read(tasklet_vec.tail) = t;
 478                __this_cpu_write(tasklet_vec.tail, &(t->next));
 479                __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 480                local_irq_enable();
 481        }
 482}
 483
 484static void tasklet_hi_action(struct softirq_action *a)
 485{
 486        struct tasklet_struct *list;
 487
 488        local_irq_disable();
 489        list = __this_cpu_read(tasklet_hi_vec.head);
 490        __this_cpu_write(tasklet_hi_vec.head, NULL);
 491        __this_cpu_write(tasklet_hi_vec.tail, &__get_cpu_var(tasklet_hi_vec).head);
 492        local_irq_enable();
 493
 494        while (list) {
 495                struct tasklet_struct *t = list;
 496
 497                list = list->next;
 498
 499                if (tasklet_trylock(t)) {
 500                        if (!atomic_read(&t->count)) {
 501                                if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 502                                        BUG();
 503                                t->func(t->data);
 504                                tasklet_unlock(t);
 505                                continue;
 506                        }
 507                        tasklet_unlock(t);
 508                }
 509
 510                local_irq_disable();
 511                t->next = NULL;
 512                *__this_cpu_read(tasklet_hi_vec.tail) = t;
 513                __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
 514                __raise_softirq_irqoff(HI_SOFTIRQ);
 515                local_irq_enable();
 516        }
 517}
 518
 519
 520void tasklet_init(struct tasklet_struct *t,
 521                  void (*func)(unsigned long), unsigned long data)
 522{
 523        t->next = NULL;
 524        t->state = 0;
 525        atomic_set(&t->count, 0);
 526        t->func = func;
 527        t->data = data;
 528}
 529
 530EXPORT_SYMBOL(tasklet_init);
 531
 532void tasklet_kill(struct tasklet_struct *t)
 533{
 534        if (in_interrupt())
 535                printk("Attempt to kill tasklet from interrupt\n");
 536
 537        while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 538                do {
 539                        yield();
 540                } while (test_bit(TASKLET_STATE_SCHED, &t->state));
 541        }
 542        tasklet_unlock_wait(t);
 543        clear_bit(TASKLET_STATE_SCHED, &t->state);
 544}
 545
 546EXPORT_SYMBOL(tasklet_kill);
 547
 548/*
 549 * tasklet_hrtimer
 550 */
 551
 552/*
 553 * The trampoline is called when the hrtimer expires. It schedules a tasklet
 554 * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
 555 * hrtimer callback, but from softirq context.
 556 */
 557static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
 558{
 559        struct tasklet_hrtimer *ttimer =
 560                container_of(timer, struct tasklet_hrtimer, timer);
 561
 562        tasklet_hi_schedule(&ttimer->tasklet);
 563        return HRTIMER_NORESTART;
 564}
 565
 566/*
 567 * Helper function which calls the hrtimer callback from
 568 * tasklet/softirq context
 569 */
 570static void __tasklet_hrtimer_trampoline(unsigned long data)
 571{
 572        struct tasklet_hrtimer *ttimer = (void *)data;
 573        enum hrtimer_restart restart;
 574
 575        restart = ttimer->function(&ttimer->timer);
 576        if (restart != HRTIMER_NORESTART)
 577                hrtimer_restart(&ttimer->timer);
 578}
 579
 580/**
 581 * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
 582 * @ttimer:      tasklet_hrtimer which is initialized
 583 * @function:    hrtimer callback function which gets called from softirq context
 584 * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
 585 * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
 586 */
 587void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
 588                          enum hrtimer_restart (*function)(struct hrtimer *),
 589                          clockid_t which_clock, enum hrtimer_mode mode)
 590{
 591        hrtimer_init(&ttimer->timer, which_clock, mode);
 592        ttimer->timer.function = __hrtimer_tasklet_trampoline;
 593        tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
 594                     (unsigned long)ttimer);
 595        ttimer->function = function;
 596}
 597EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
 598
 599/*
 600 * Remote softirq bits
 601 */
 602
 603DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
 604EXPORT_PER_CPU_SYMBOL(softirq_work_list);
 605
 606static void __local_trigger(struct call_single_data *cp, int softirq)
 607{
 608        struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
 609
 610        list_add_tail(&cp->list, head);
 611
 612        /* Trigger the softirq only if the list was previously empty.  */
 613        if (head->next == &cp->list)
 614                raise_softirq_irqoff(softirq);
 615}
 616
 617#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
 618static void remote_softirq_receive(void *data)
 619{
 620        struct call_single_data *cp = data;
 621        unsigned long flags;
 622        int softirq;
 623
 624        softirq = cp->priv;
 625
 626        local_irq_save(flags);
 627        __local_trigger(cp, softirq);
 628        local_irq_restore(flags);
 629}
 630
 631static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 632{
 633        if (cpu_online(cpu)) {
 634                cp->func = remote_softirq_receive;
 635                cp->info = cp;
 636                cp->flags = 0;
 637                cp->priv = softirq;
 638
 639                __smp_call_function_single(cpu, cp, 0);
 640                return 0;
 641        }
 642        return 1;
 643}
 644#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
 645static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 646{
 647        return 1;
 648}
 649#endif
 650
 651/**
 652 * __send_remote_softirq - try to schedule softirq work on a remote cpu
 653 * @cp: private SMP call function data area
 654 * @cpu: the remote cpu
 655 * @this_cpu: the currently executing cpu
 656 * @softirq: the softirq for the work
 657 *
 658 * Attempt to schedule softirq work on a remote cpu.  If this cannot be
 659 * done, the work is instead queued up on the local cpu.
 660 *
 661 * Interrupts must be disabled.
 662 */
 663void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
 664{
 665        if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
 666                __local_trigger(cp, softirq);
 667}
 668EXPORT_SYMBOL(__send_remote_softirq);
 669
 670/**
 671 * send_remote_softirq - try to schedule softirq work on a remote cpu
 672 * @cp: private SMP call function data area
 673 * @cpu: the remote cpu
 674 * @softirq: the softirq for the work
 675 *
 676 * Like __send_remote_softirq except that disabling interrupts and
 677 * computing the current cpu is done for the caller.
 678 */
 679void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 680{
 681        unsigned long flags;
 682        int this_cpu;
 683
 684        local_irq_save(flags);
 685        this_cpu = smp_processor_id();
 686        __send_remote_softirq(cp, cpu, this_cpu, softirq);
 687        local_irq_restore(flags);
 688}
 689EXPORT_SYMBOL(send_remote_softirq);
 690
 691static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
 692                                               unsigned long action, void *hcpu)
 693{
 694        /*
 695         * If a CPU goes away, splice its entries to the current CPU
 696         * and trigger a run of the softirq
 697         */
 698        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
 699                int cpu = (unsigned long) hcpu;
 700                int i;
 701
 702                local_irq_disable();
 703                for (i = 0; i < NR_SOFTIRQS; i++) {
 704                        struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
 705                        struct list_head *local_head;
 706
 707                        if (list_empty(head))
 708                                continue;
 709
 710                        local_head = &__get_cpu_var(softirq_work_list[i]);
 711                        list_splice_init(head, local_head);
 712                        raise_softirq_irqoff(i);
 713                }
 714                local_irq_enable();
 715        }
 716
 717        return NOTIFY_OK;
 718}
 719
 720static struct notifier_block __cpuinitdata remote_softirq_cpu_notifier = {
 721        .notifier_call  = remote_softirq_cpu_notify,
 722};
 723
 724void __init softirq_init(void)
 725{
 726        int cpu;
 727
 728        for_each_possible_cpu(cpu) {
 729                int i;
 730
 731                per_cpu(tasklet_vec, cpu).tail =
 732                        &per_cpu(tasklet_vec, cpu).head;
 733                per_cpu(tasklet_hi_vec, cpu).tail =
 734                        &per_cpu(tasklet_hi_vec, cpu).head;
 735                for (i = 0; i < NR_SOFTIRQS; i++)
 736                        INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
 737        }
 738
 739        register_hotcpu_notifier(&remote_softirq_cpu_notifier);
 740
 741        open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 742        open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 743}
 744
 745static int run_ksoftirqd(void * __bind_cpu)
 746{
 747        set_current_state(TASK_INTERRUPTIBLE);
 748
 749        while (!kthread_should_stop()) {
 750                preempt_disable();
 751                if (!local_softirq_pending()) {
 752                        schedule_preempt_disabled();
 753                }
 754
 755                __set_current_state(TASK_RUNNING);
 756
 757                while (local_softirq_pending()) {
 758                        /* Preempt disable stops cpu going offline.
 759                           If already offline, we'll be on wrong CPU:
 760                           don't process */
 761                        if (cpu_is_offline((long)__bind_cpu))
 762                                goto wait_to_die;
 763                        local_irq_disable();
 764                        if (local_softirq_pending())
 765                                __do_softirq();
 766                        local_irq_enable();
 767                        sched_preempt_enable_no_resched();
 768                        cond_resched();
 769                        preempt_disable();
 770                        rcu_note_context_switch((long)__bind_cpu);
 771                }
 772                preempt_enable();
 773                set_current_state(TASK_INTERRUPTIBLE);
 774        }
 775        __set_current_state(TASK_RUNNING);
 776        return 0;
 777
 778wait_to_die:
 779        preempt_enable();
 780        /* Wait for kthread_stop */
 781        set_current_state(TASK_INTERRUPTIBLE);
 782        while (!kthread_should_stop()) {
 783                schedule();
 784                set_current_state(TASK_INTERRUPTIBLE);
 785        }
 786        __set_current_state(TASK_RUNNING);
 787        return 0;
 788}
 789
 790#ifdef CONFIG_HOTPLUG_CPU
 791/*
 792 * tasklet_kill_immediate is called to remove a tasklet which can already be
 793 * scheduled for execution on @cpu.
 794 *
 795 * Unlike tasklet_kill, this function removes the tasklet
 796 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 797 *
 798 * When this function is called, @cpu must be in the CPU_DEAD state.
 799 */
 800void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 801{
 802        struct tasklet_struct **i;
 803
 804        BUG_ON(cpu_online(cpu));
 805        BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 806
 807        if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 808                return;
 809
 810        /* CPU is dead, so no lock needed. */
 811        for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 812                if (*i == t) {
 813                        *i = t->next;
 814                        /* If this was the tail element, move the tail ptr */
 815                        if (*i == NULL)
 816                                per_cpu(tasklet_vec, cpu).tail = i;
 817                        return;
 818                }
 819        }
 820        BUG();
 821}
 822
 823static void takeover_tasklets(unsigned int cpu)
 824{
 825        /* CPU is dead, so no lock needed. */
 826        local_irq_disable();
 827
 828        /* Find end, append list for that CPU. */
 829        if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 830                *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 831                this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 832                per_cpu(tasklet_vec, cpu).head = NULL;
 833                per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 834        }
 835        raise_softirq_irqoff(TASKLET_SOFTIRQ);
 836
 837        if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 838                *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 839                __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 840                per_cpu(tasklet_hi_vec, cpu).head = NULL;
 841                per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 842        }
 843        raise_softirq_irqoff(HI_SOFTIRQ);
 844
 845        local_irq_enable();
 846}
 847#endif /* CONFIG_HOTPLUG_CPU */
 848
 849static int __cpuinit cpu_callback(struct notifier_block *nfb,
 850                                  unsigned long action,
 851                                  void *hcpu)
 852{
 853        int hotcpu = (unsigned long)hcpu;
 854        struct task_struct *p;
 855
 856        switch (action) {
 857        case CPU_UP_PREPARE:
 858        case CPU_UP_PREPARE_FROZEN:
 859                p = kthread_create_on_node(run_ksoftirqd,
 860                                           hcpu,
 861                                           cpu_to_node(hotcpu),
 862                                           "ksoftirqd/%d", hotcpu);
 863                if (IS_ERR(p)) {
 864                        printk("ksoftirqd for %i failed\n", hotcpu);
 865                        return notifier_from_errno(PTR_ERR(p));
 866                }
 867                kthread_bind(p, hotcpu);
 868                per_cpu(ksoftirqd, hotcpu) = p;
 869                break;
 870        case CPU_ONLINE:
 871        case CPU_ONLINE_FROZEN:
 872                wake_up_process(per_cpu(ksoftirqd, hotcpu));
 873                break;
 874#ifdef CONFIG_HOTPLUG_CPU
 875        case CPU_UP_CANCELED:
 876        case CPU_UP_CANCELED_FROZEN:
 877                if (!per_cpu(ksoftirqd, hotcpu))
 878                        break;
 879                /* Unbind so it can run.  Fall thru. */
 880                kthread_bind(per_cpu(ksoftirqd, hotcpu),
 881                             cpumask_any(cpu_online_mask));
 882        case CPU_DEAD:
 883        case CPU_DEAD_FROZEN: {
 884                static const struct sched_param param = {
 885                        .sched_priority = MAX_RT_PRIO-1
 886                };
 887
 888                p = per_cpu(ksoftirqd, hotcpu);
 889                per_cpu(ksoftirqd, hotcpu) = NULL;
 890                sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
 891                kthread_stop(p);
 892                takeover_tasklets(hotcpu);
 893                break;
 894        }
 895#endif /* CONFIG_HOTPLUG_CPU */
 896        }
 897        return NOTIFY_OK;
 898}
 899
 900static struct notifier_block __cpuinitdata cpu_nfb = {
 901        .notifier_call = cpu_callback
 902};
 903
 904static __init int spawn_ksoftirqd(void)
 905{
 906        void *cpu = (void *)(long)smp_processor_id();
 907        int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 908
 909        BUG_ON(err != NOTIFY_OK);
 910        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 911        register_cpu_notifier(&cpu_nfb);
 912        return 0;
 913}
 914early_initcall(spawn_ksoftirqd);
 915
 916/*
 917 * [ These __weak aliases are kept in a separate compilation unit, so that
 918 *   GCC does not inline them incorrectly. ]
 919 */
 920
 921int __init __weak early_irq_init(void)
 922{
 923        return 0;
 924}
 925
 926#ifdef CONFIG_GENERIC_HARDIRQS
 927int __init __weak arch_probe_nr_irqs(void)
 928{
 929        return NR_IRQS_LEGACY;
 930}
 931
 932int __init __weak arch_early_irq_init(void)
 933{
 934        return 0;
 935}
 936#endif
 937
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