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