kernel/softirq.c

   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
  52 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
  53 EXPORT_SYMBOL(irq_stat);
  54 #endif
  55
  56 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
  57
  58 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  59
  60 const char * const softirq_to_name[NR_SOFTIRQS] = {
  61         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
  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  */
  71 static 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  * If ksoftirqd is scheduled, we do not want to process pending softirqs
  82  * right now. Let ksoftirqd handle this at its own rate, to get fairness.
  83  */
  84 static bool ksoftirqd_running(void)
  85 {
  86         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  87
  88         return tsk && (tsk->state == TASK_RUNNING);
  89 }
  90
  91 /*
  92  * preempt_count and SOFTIRQ_OFFSET usage:
  93  * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
  94  *   softirq processing.
  95  * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
  96  *   on local_bh_disable or local_bh_enable.
  97  * This lets us distinguish between whether we are currently processing
  98  * softirq and whether we just have bh disabled.
  99  */
 100
 101 /*
 102  * This one is for softirq.c-internal use,
 103  * where hardirqs are disabled legitimately:
 104  */
 105 #ifdef CONFIG_TRACE_IRQFLAGS
 106 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 107 {
 108         unsigned long flags;
 109
 110         WARN_ON_ONCE(in_irq());
 111
 112         raw_local_irq_save(flags);
 113         /*
 114          * The preempt tracer hooks into preempt_count_add and will break
 115          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 116          * is set and before current->softirq_enabled is cleared.
 117          * We must manually increment preempt_count here and manually
 118          * call the trace_preempt_off later.
 119          */
 120         __preempt_count_add(cnt);
 121         /*
 122          * Were softirqs turned off above:
 123          */
 124         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 125                 trace_softirqs_off(ip);
 126         raw_local_irq_restore(flags);
 127
 128         if (preempt_count() == cnt) {
 129 #ifdef CONFIG_DEBUG_PREEMPT
 130                 current->preempt_disable_ip = get_lock_parent_ip();
 131 #endif
 132                 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
 133         }
 134 }
 135 EXPORT_SYMBOL(__local_bh_disable_ip);
 136 #endif /* CONFIG_TRACE_IRQFLAGS */
 137
 138 static void __local_bh_enable(unsigned int cnt)
 139 {
 140         WARN_ON_ONCE(!irqs_disabled());
 141
 142         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 143                 trace_softirqs_on(_RET_IP_);
 144         preempt_count_sub(cnt);
 145 }
 146
 147 /*
 148  * Special-case - softirqs can safely be enabled in
 149  * cond_resched_softirq(), or by __do_softirq(),
 150  * without processing still-pending softirqs:
 151  */
 152 void _local_bh_enable(void)
 153 {
 154         WARN_ON_ONCE(in_irq());
 155         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 156 }
 157 EXPORT_SYMBOL(_local_bh_enable);
 158
 159 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 160 {
 161         WARN_ON_ONCE(in_irq() || irqs_disabled());
 162 #ifdef CONFIG_TRACE_IRQFLAGS
 163         local_irq_disable();
 164 #endif
 165         /*
 166          * Are softirqs going to be turned on now:
 167          */
 168         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 169                 trace_softirqs_on(ip);
 170         /*
 171          * Keep preemption disabled until we are done with
 172          * softirq processing:
 173          */
 174         preempt_count_sub(cnt - 1);
 175
 176         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 177                 /*
 178                  * Run softirq if any pending. And do it in its own stack
 179                  * as we may be calling this deep in a task call stack already.
 180                  */
 181                 do_softirq();
 182         }
 183
 184         preempt_count_dec();
 185 #ifdef CONFIG_TRACE_IRQFLAGS
 186         local_irq_enable();
 187 #endif
 188         preempt_check_resched();
 189 }
 190 EXPORT_SYMBOL(__local_bh_enable_ip);
 191
 192 /*
 193  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 194  * but break the loop if need_resched() is set or after 2 ms.
 195  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 196  * certain cases, such as stop_machine(), jiffies may cease to
 197  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 198  * well to make sure we eventually return from this method.
 199  *
 200  * These limits have 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_TIME  msecs_to_jiffies(2)
 206 #define MAX_SOFTIRQ_RESTART 10
 207
 208 #ifdef CONFIG_TRACE_IRQFLAGS
 209 /*
 210  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 211  * to keep the lockdep irq context tracking as tight as possible in order to
 212  * not miss-qualify lock contexts and miss possible deadlocks.
 213  */
 214
 215 static inline bool lockdep_softirq_start(void)
 216 {
 217         bool in_hardirq = false;
 218
 219         if (trace_hardirq_context(current)) {
 220                 in_hardirq = true;
 221                 trace_hardirq_exit();
 222         }
 223
 224         lockdep_softirq_enter();
 225
 226         return in_hardirq;
 227 }
 228
 229 static inline void lockdep_softirq_end(bool in_hardirq)
 230 {
 231         lockdep_softirq_exit();
 232
 233         if (in_hardirq)
 234                 trace_hardirq_enter();
 235 }
 236 #else
 237 static inline bool lockdep_softirq_start(void) { return false; }
 238 static inline void lockdep_softirq_end(bool in_hardirq) { }
 239 #endif
 240
 241 asmlinkage __visible void __softirq_entry __do_softirq(void)
 242 {
 243         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 244         unsigned long old_flags = current->flags;
 245         int max_restart = MAX_SOFTIRQ_RESTART;
 246         struct softirq_action *h;
 247         bool in_hardirq;
 248         __u32 pending;
 249         int softirq_bit;
 250
 251         /*
 252          * Mask out PF_MEMALLOC s current task context is borrowed for the
 253          * softirq. A softirq handled such as network RX might set PF_MEMALLOC
 254          * again if the socket is related to swap
 255          */
 256         current->flags &= ~PF_MEMALLOC;
 257
 258         pending = local_softirq_pending();
 259         account_irq_enter_time(current);
 260
 261         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 262         in_hardirq = lockdep_softirq_start();
 263
 264 restart:
 265         /* Reset the pending bitmask before enabling irqs */
 266         set_softirq_pending(0);
 267
 268         local_irq_enable();
 269
 270         h = softirq_vec;
 271
 272         while ((softirq_bit = ffs(pending))) {
 273                 unsigned int vec_nr;
 274                 int prev_count;
 275
 276                 h += softirq_bit - 1;
 277
 278                 vec_nr = h - softirq_vec;
 279                 prev_count = preempt_count();
 280
 281                 kstat_incr_softirqs_this_cpu(vec_nr);
 282
 283                 trace_softirq_entry(vec_nr);
 284                 h->action(h);
 285                 trace_softirq_exit(vec_nr);
 286                 if (unlikely(prev_count != preempt_count())) {
 287                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 288                                vec_nr, softirq_to_name[vec_nr], h->action,
 289                                prev_count, preempt_count());
 290                         preempt_count_set(prev_count);
 291                 }
 292                 h++;
 293                 pending >>= softirq_bit;
 294         }
 295
 296         rcu_bh_qs();
 297         local_irq_disable();
 298
 299         pending = local_softirq_pending();
 300         if (pending) {
 301                 if (time_before(jiffies, end) && !need_resched() &&
 302                     --max_restart)
 303                         goto restart;
 304
 305                 wakeup_softirqd();
 306         }
 307
 308         lockdep_softirq_end(in_hardirq);
 309         account_irq_exit_time(current);
 310         __local_bh_enable(SOFTIRQ_OFFSET);
 311         WARN_ON_ONCE(in_interrupt());
 312         current_restore_flags(old_flags, PF_MEMALLOC);
 313 }
 314
 315 asmlinkage __visible void do_softirq(void)
 316 {
 317         __u32 pending;
 318         unsigned long flags;
 319
 320         if (in_interrupt())
 321                 return;
 322
 323         local_irq_save(flags);
 324
 325         pending = local_softirq_pending();
 326
 327         if (pending && !ksoftirqd_running())
 328                 do_softirq_own_stack();
 329
 330         local_irq_restore(flags);
 331 }
 332
 333 /*
 334  * Enter an interrupt context.
 335  */
 336 void irq_enter(void)
 337 {
 338         rcu_irq_enter();
 339         if (is_idle_task(current) && !in_interrupt()) {
 340                 /*
 341                  * Prevent raise_softirq from needlessly waking up ksoftirqd
 342                  * here, as softirq will be serviced on return from interrupt.
 343                  */
 344                 local_bh_disable();
 345                 tick_irq_enter();
 346                 _local_bh_enable();
 347         }
 348
 349         __irq_enter();
 350 }
 351
 352 static inline void invoke_softirq(void)
 353 {
 354         if (ksoftirqd_running())
 355                 return;
 356
 357         if (!force_irqthreads) {
 358 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 359                 /*
 360                  * We can safely execute softirq on the current stack if
 361                  * it is the irq stack, because it should be near empty
 362                  * at this stage.
 363                  */
 364                 __do_softirq();
 365 #else
 366                 /*
 367                  * Otherwise, irq_exit() is called on the task stack that can
 368                  * be potentially deep already. So call softirq in its own stack
 369                  * to prevent from any overrun.
 370                  */
 371                 do_softirq_own_stack();
 372 #endif
 373         } else {
 374                 wakeup_softirqd();
 375         }
 376 }
 377
 378 static inline void tick_irq_exit(void)
 379 {
 380 #ifdef CONFIG_NO_HZ_COMMON
 381         int cpu = smp_processor_id();
 382
 383         /* Make sure that timer wheel updates are propagated */
 384         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 385                 if (!in_interrupt())
 386                         tick_nohz_irq_exit();
 387         }
 388 #endif
 389 }
 390
 391 /*
 392  * Exit an interrupt context. Process softirqs if needed and possible:
 393  */
 394 void irq_exit(void)
 395 {
 396 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 397         local_irq_disable();
 398 #else
 399         WARN_ON_ONCE(!irqs_disabled());
 400 #endif
 401
 402         account_irq_exit_time(current);
 403         preempt_count_sub(HARDIRQ_OFFSET);
 404         if (!in_interrupt() && local_softirq_pending())
 405                 invoke_softirq();
 406
 407         tick_irq_exit();
 408         rcu_irq_exit();
 409         trace_hardirq_exit(); /* must be last! */
 410 }
 411
 412 /*
 413  * This function must run with irqs disabled!
 414  */
 415 inline void raise_softirq_irqoff(unsigned int nr)
 416 {
 417         __raise_softirq_irqoff(nr);
 418
 419         /*
 420          * If we're in an interrupt or softirq, we're done
 421          * (this also catches softirq-disabled code). We will
 422          * actually run the softirq once we return from
 423          * the irq or softirq.
 424          *
 425          * Otherwise we wake up ksoftirqd to make sure we
 426          * schedule the softirq soon.
 427          */
 428         if (!in_interrupt())
 429                 wakeup_softirqd();
 430 }
 431
 432 void raise_softirq(unsigned int nr)
 433 {
 434         unsigned long flags;
 435
 436         local_irq_save(flags);
 437         raise_softirq_irqoff(nr);
 438         local_irq_restore(flags);
 439 }
 440
 441 void __raise_softirq_irqoff(unsigned int nr)
 442 {
 443         trace_softirq_raise(nr);
 444         or_softirq_pending(1UL << nr);
 445 }
 446
 447 void open_softirq(int nr, void (*action)(struct softirq_action *))
 448 {
 449         softirq_vec[nr].action = action;
 450 }
 451
 452 /*
 453  * Tasklets
 454  */
 455 struct tasklet_head {
 456         struct tasklet_struct *head;
 457         struct tasklet_struct **tail;
 458 };
 459
 460 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 461 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 462
 463 void __tasklet_schedule(struct tasklet_struct *t)
 464 {
 465         unsigned long flags;
 466
 467         local_irq_save(flags);
 468         t->next = NULL;
 469         *__this_cpu_read(tasklet_vec.tail) = t;
 470         __this_cpu_write(tasklet_vec.tail, &(t->next));
 471         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 472         local_irq_restore(flags);
 473 }
 474 EXPORT_SYMBOL(__tasklet_schedule);
 475
 476 void __tasklet_hi_schedule(struct tasklet_struct *t)
 477 {
 478         unsigned long flags;
 479
 480         local_irq_save(flags);
 481         t->next = NULL;
 482         *__this_cpu_read(tasklet_hi_vec.tail) = t;
 483         __this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
 484         raise_softirq_irqoff(HI_SOFTIRQ);
 485         local_irq_restore(flags);
 486 }
 487 EXPORT_SYMBOL(__tasklet_hi_schedule);
 488
 489 static __latent_entropy void tasklet_action(struct softirq_action *a)
 490 {
 491         struct tasklet_struct *list;
 492
 493         local_irq_disable();
 494         list = __this_cpu_read(tasklet_vec.head);
 495         __this_cpu_write(tasklet_vec.head, NULL);
 496         __this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
 497         local_irq_enable();
 498
 499         while (list) {
 500                 struct tasklet_struct *t = list;
 501
 502                 list = list->next;
 503
 504                 if (tasklet_trylock(t)) {
 505                         if (!atomic_read(&t->count)) {
 506                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 507                                                         &t->state))
 508                                         BUG();
 509                                 t->func(t->data);
 510                                 tasklet_unlock(t);
 511                                 continue;
 512                         }
 513                         tasklet_unlock(t);
 514                 }
 515
 516                 local_irq_disable();
 517                 t->next = NULL;
 518                 *__this_cpu_read(tasklet_vec.tail) = t;
 519                 __this_cpu_write(tasklet_vec.tail, &(t->next));
 520                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 521                 local_irq_enable();
 522         }
 523 }
 524
 525 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 526 {
 527         struct tasklet_struct *list;
 528
 529         local_irq_disable();
 530         list = __this_cpu_read(tasklet_hi_vec.head);
 531         __this_cpu_write(tasklet_hi_vec.head, NULL);
 532         __this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
 533         local_irq_enable();
 534
 535         while (list) {
 536                 struct tasklet_struct *t = list;
 537
 538                 list = list->next;
 539
 540                 if (tasklet_trylock(t)) {
 541                         if (!atomic_read(&t->count)) {
 542                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 543                                                         &t->state))
 544                                         BUG();
 545                                 t->func(t->data);
 546                                 tasklet_unlock(t);
 547                                 continue;
 548                         }
 549                         tasklet_unlock(t);
 550                 }
 551
 552                 local_irq_disable();
 553                 t->next = NULL;
 554                 *__this_cpu_read(tasklet_hi_vec.tail) = t;
 555                 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
 556                 __raise_softirq_irqoff(HI_SOFTIRQ);
 557                 local_irq_enable();
 558         }
 559 }
 560
 561 void tasklet_init(struct tasklet_struct *t,
 562                   void (*func)(unsigned long), unsigned long data)
 563 {
 564         t->next = NULL;
 565         t->state = 0;
 566         atomic_set(&t->count, 0);
 567         t->func = func;
 568         t->data = data;
 569 }
 570 EXPORT_SYMBOL(tasklet_init);
 571
 572 void tasklet_kill(struct tasklet_struct *t)
 573 {
 574         if (in_interrupt())
 575                 pr_notice("Attempt to kill tasklet from interrupt\n");
 576
 577         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 578                 do {
 579                         yield();
 580                 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
 581         }
 582         tasklet_unlock_wait(t);
 583         clear_bit(TASKLET_STATE_SCHED, &t->state);
 584 }
 585 EXPORT_SYMBOL(tasklet_kill);
 586
 587 /*
 588  * tasklet_hrtimer
 589  */
 590
 591 /*
 592  * The trampoline is called when the hrtimer expires. It schedules a tasklet
 593  * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
 594  * hrtimer callback, but from softirq context.
 595  */
 596 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
 597 {
 598         struct tasklet_hrtimer *ttimer =
 599                 container_of(timer, struct tasklet_hrtimer, timer);
 600
 601         tasklet_hi_schedule(&ttimer->tasklet);
 602         return HRTIMER_NORESTART;
 603 }
 604
 605 /*
 606  * Helper function which calls the hrtimer callback from
 607  * tasklet/softirq context
 608  */
 609 static void __tasklet_hrtimer_trampoline(unsigned long data)
 610 {
 611         struct tasklet_hrtimer *ttimer = (void *)data;
 612         enum hrtimer_restart restart;
 613
 614         restart = ttimer->function(&ttimer->timer);
 615         if (restart != HRTIMER_NORESTART)
 616                 hrtimer_restart(&ttimer->timer);
 617 }
 618
 619 /**
 620  * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
 621  * @ttimer:      tasklet_hrtimer which is initialized
 622  * @function:    hrtimer callback function which gets called from softirq context
 623  * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
 624  * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
 625  */
 626 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
 627                           enum hrtimer_restart (*function)(struct hrtimer *),
 628                           clockid_t which_clock, enum hrtimer_mode mode)
 629 {
 630         hrtimer_init(&ttimer->timer, which_clock, mode);
 631         ttimer->timer.function = __hrtimer_tasklet_trampoline;
 632         tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
 633                      (unsigned long)ttimer);
 634         ttimer->function = function;
 635 }
 636 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
 637
 638 void __init softirq_init(void)
 639 {
 640         int cpu;
 641
 642         for_each_possible_cpu(cpu) {
 643                 per_cpu(tasklet_vec, cpu).tail =
 644                         &per_cpu(tasklet_vec, cpu).head;
 645                 per_cpu(tasklet_hi_vec, cpu).tail =
 646                         &per_cpu(tasklet_hi_vec, cpu).head;
 647         }
 648
 649         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 650         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 651 }
 652
 653 static int ksoftirqd_should_run(unsigned int cpu)
 654 {
 655         return local_softirq_pending();
 656 }
 657
 658 static void run_ksoftirqd(unsigned int cpu)
 659 {
 660         local_irq_disable();
 661         if (local_softirq_pending()) {
 662                 /*
 663                  * We can safely run softirq on inline stack, as we are not deep
 664                  * in the task stack here.
 665                  */
 666                 __do_softirq();
 667                 local_irq_enable();
 668                 cond_resched_rcu_qs();
 669                 return;
 670         }
 671         local_irq_enable();
 672 }
 673
 674 #ifdef CONFIG_HOTPLUG_CPU
 675 /*
 676  * tasklet_kill_immediate is called to remove a tasklet which can already be
 677  * scheduled for execution on @cpu.
 678  *
 679  * Unlike tasklet_kill, this function removes the tasklet
 680  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 681  *
 682  * When this function is called, @cpu must be in the CPU_DEAD state.
 683  */
 684 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 685 {
 686         struct tasklet_struct **i;
 687
 688         BUG_ON(cpu_online(cpu));
 689         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 690
 691         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 692                 return;
 693
 694         /* CPU is dead, so no lock needed. */
 695         for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 696                 if (*i == t) {
 697                         *i = t->next;
 698                         /* If this was the tail element, move the tail ptr */
 699                         if (*i == NULL)
 700                                 per_cpu(tasklet_vec, cpu).tail = i;
 701                         return;
 702                 }
 703         }
 704         BUG();
 705 }
 706
 707 static int takeover_tasklets(unsigned int cpu)
 708 {
 709         /* CPU is dead, so no lock needed. */
 710         local_irq_disable();
 711
 712         /* Find end, append list for that CPU. */
 713         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 714                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 715                 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 716                 per_cpu(tasklet_vec, cpu).head = NULL;
 717                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 718         }
 719         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 720
 721         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 722                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 723                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 724                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 725                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 726         }
 727         raise_softirq_irqoff(HI_SOFTIRQ);
 728
 729         local_irq_enable();
 730         return 0;
 731 }
 732 #else
 733 #define takeover_tasklets       NULL
 734 #endif /* CONFIG_HOTPLUG_CPU */
 735
 736 static struct smp_hotplug_thread softirq_threads = {
 737         .store                  = &ksoftirqd,
 738         .thread_should_run      = ksoftirqd_should_run,
 739         .thread_fn              = run_ksoftirqd,
 740         .thread_comm            = "ksoftirqd/%u",
 741 };
 742
 743 static __init int spawn_ksoftirqd(void)
 744 {
 745         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 746                                   takeover_tasklets);
 747         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 748
 749         return 0;
 750 }
 751 early_initcall(spawn_ksoftirqd);
 752
 753 /*
 754  * [ These __weak aliases are kept in a separate compilation unit, so that
 755  *   GCC does not inline them incorrectly. ]
 756  */
 757
 758 int __init __weak early_irq_init(void)
 759 {
 760         return 0;
 761 }
 762
 763 int __init __weak arch_probe_nr_irqs(void)
 764 {
 765         return NR_IRQS_LEGACY;
 766 }
 767
 768 int __init __weak arch_early_irq_init(void)
 769 {
 770         return 0;
 771 }
 772
 773 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 774 {
 775         return from;
 776 }