kernel/softirq.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *      linux/kernel/softirq.c
   4  *
   5  *      Copyright (C) 1992 Linus Torvalds
   6  *
   7  *      Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
   8  */
   9
  10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  11
  12 #include <linux/export.h>
  13 #include <linux/kernel_stat.h>
  14 #include <linux/interrupt.h>
  15 #include <linux/init.h>
  16 #include <linux/mm.h>
  17 #include <linux/notifier.h>
  18 #include <linux/percpu.h>
  19 #include <linux/cpu.h>
  20 #include <linux/freezer.h>
  21 #include <linux/kthread.h>
  22 #include <linux/rcupdate.h>
  23 #include <linux/ftrace.h>
  24 #include <linux/smp.h>
  25 #include <linux/smpboot.h>
  26 #include <linux/tick.h>
  27 #include <linux/irq.h>
  28 #include <linux/wait_bit.h>
  29
  30 #include <asm/softirq_stack.h>
  31
  32 #define CREATE_TRACE_POINTS
  33 #include <trace/events/irq.h>
  34
  35 /*
  36    - No shared variables, all the data are CPU local.
  37    - If a softirq needs serialization, let it serialize itself
  38      by its own spinlocks.
  39    - Even if softirq is serialized, only local cpu is marked for
  40      execution. Hence, we get something sort of weak cpu binding.
  41      Though it is still not clear, will it result in better locality
  42      or will not.
  43
  44    Examples:
  45    - NET RX softirq. It is multithreaded and does not require
  46      any global serialization.
  47    - NET TX softirq. It kicks software netdevice queues, hence
  48      it is logically serialized per device, but this serialization
  49      is invisible to common code.
  50    - Tasklets: serialized wrt itself.
  51  */
  52
  53 #ifndef __ARCH_IRQ_STAT
  54 DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat);
  55 EXPORT_PER_CPU_SYMBOL(irq_stat);
  56 #endif
  57
  58 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
  59
  60 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  61
  62 const char * const softirq_to_name[NR_SOFTIRQS] = {
  63         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
  64         "TASKLET", "SCHED", "HRTIMER", "RCU"
  65 };
  66
  67 /*
  68  * we cannot loop indefinitely here to avoid userspace starvation,
  69  * but we also don't want to introduce a worst case 1/HZ latency
  70  * to the pending events, so lets the scheduler to balance
  71  * the softirq load for us.
  72  */
  73 static void wakeup_softirqd(void)
  74 {
  75         /* Interrupts are disabled: no need to stop preemption */
  76         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  77
  78         if (tsk && tsk->state != TASK_RUNNING)
  79                 wake_up_process(tsk);
  80 }
  81
  82 /*
  83  * If ksoftirqd is scheduled, we do not want to process pending softirqs
  84  * right now. Let ksoftirqd handle this at its own rate, to get fairness,
  85  * unless we're doing some of the synchronous softirqs.
  86  */
  87 #define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
  88 static bool ksoftirqd_running(unsigned long pending)
  89 {
  90         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  91
  92         if (pending & SOFTIRQ_NOW_MASK)
  93                 return false;
  94         return tsk && (tsk->state == TASK_RUNNING) &&
  95                 !__kthread_should_park(tsk);
  96 }
  97
  98 #ifdef CONFIG_TRACE_IRQFLAGS
  99 DEFINE_PER_CPU(int, hardirqs_enabled);
 100 DEFINE_PER_CPU(int, hardirq_context);
 101 EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
 102 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
 103 #endif
 104
 105 /*
 106  * preempt_count and SOFTIRQ_OFFSET usage:
 107  * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
 108  *   softirq processing.
 109  * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
 110  *   on local_bh_disable or local_bh_enable.
 111  * This lets us distinguish between whether we are currently processing
 112  * softirq and whether we just have bh disabled.
 113  */
 114
 115 #ifdef CONFIG_TRACE_IRQFLAGS
 116 /*
 117  * This is for softirq.c-internal use, where hardirqs are disabled
 118  * legitimately:
 119  */
 120 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 121 {
 122         unsigned long flags;
 123
 124         WARN_ON_ONCE(in_irq());
 125
 126         raw_local_irq_save(flags);
 127         /*
 128          * The preempt tracer hooks into preempt_count_add and will break
 129          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 130          * is set and before current->softirq_enabled is cleared.
 131          * We must manually increment preempt_count here and manually
 132          * call the trace_preempt_off later.
 133          */
 134         __preempt_count_add(cnt);
 135         /*
 136          * Were softirqs turned off above:
 137          */
 138         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 139                 lockdep_softirqs_off(ip);
 140         raw_local_irq_restore(flags);
 141
 142         if (preempt_count() == cnt) {
 143 #ifdef CONFIG_DEBUG_PREEMPT
 144                 current->preempt_disable_ip = get_lock_parent_ip();
 145 #endif
 146                 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
 147         }
 148 }
 149 EXPORT_SYMBOL(__local_bh_disable_ip);
 150 #endif /* CONFIG_TRACE_IRQFLAGS */
 151
 152 static void __local_bh_enable(unsigned int cnt)
 153 {
 154         lockdep_assert_irqs_disabled();
 155
 156         if (preempt_count() == cnt)
 157                 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 158
 159         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 160                 lockdep_softirqs_on(_RET_IP_);
 161
 162         __preempt_count_sub(cnt);
 163 }
 164
 165 /*
 166  * Special-case - softirqs can safely be enabled by __do_softirq(),
 167  * without processing still-pending softirqs:
 168  */
 169 void _local_bh_enable(void)
 170 {
 171         WARN_ON_ONCE(in_irq());
 172         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 173 }
 174 EXPORT_SYMBOL(_local_bh_enable);
 175
 176 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 177 {
 178         WARN_ON_ONCE(in_irq());
 179         lockdep_assert_irqs_enabled();
 180 #ifdef CONFIG_TRACE_IRQFLAGS
 181         local_irq_disable();
 182 #endif
 183         /*
 184          * Are softirqs going to be turned on now:
 185          */
 186         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 187                 lockdep_softirqs_on(ip);
 188         /*
 189          * Keep preemption disabled until we are done with
 190          * softirq processing:
 191          */
 192         __preempt_count_sub(cnt - 1);
 193
 194         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 195                 /*
 196                  * Run softirq if any pending. And do it in its own stack
 197                  * as we may be calling this deep in a task call stack already.
 198                  */
 199                 do_softirq();
 200         }
 201
 202         preempt_count_dec();
 203 #ifdef CONFIG_TRACE_IRQFLAGS
 204         local_irq_enable();
 205 #endif
 206         preempt_check_resched();
 207 }
 208 EXPORT_SYMBOL(__local_bh_enable_ip);
 209
 210 static inline void invoke_softirq(void)
 211 {
 212         if (ksoftirqd_running(local_softirq_pending()))
 213                 return;
 214
 215         if (!force_irqthreads) {
 216 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 217                 /*
 218                  * We can safely execute softirq on the current stack if
 219                  * it is the irq stack, because it should be near empty
 220                  * at this stage.
 221                  */
 222                 __do_softirq();
 223 #else
 224                 /*
 225                  * Otherwise, irq_exit() is called on the task stack that can
 226                  * be potentially deep already. So call softirq in its own stack
 227                  * to prevent from any overrun.
 228                  */
 229                 do_softirq_own_stack();
 230 #endif
 231         } else {
 232                 wakeup_softirqd();
 233         }
 234 }
 235
 236 asmlinkage __visible void do_softirq(void)
 237 {
 238         __u32 pending;
 239         unsigned long flags;
 240
 241         if (in_interrupt())
 242                 return;
 243
 244         local_irq_save(flags);
 245
 246         pending = local_softirq_pending();
 247
 248         if (pending && !ksoftirqd_running(pending))
 249                 do_softirq_own_stack();
 250
 251         local_irq_restore(flags);
 252 }
 253
 254 /*
 255  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 256  * but break the loop if need_resched() is set or after 2 ms.
 257  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 258  * certain cases, such as stop_machine(), jiffies may cease to
 259  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 260  * well to make sure we eventually return from this method.
 261  *
 262  * These limits have been established via experimentation.
 263  * The two things to balance is latency against fairness -
 264  * we want to handle softirqs as soon as possible, but they
 265  * should not be able to lock up the box.
 266  */
 267 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 268 #define MAX_SOFTIRQ_RESTART 10
 269
 270 #ifdef CONFIG_TRACE_IRQFLAGS
 271 /*
 272  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 273  * to keep the lockdep irq context tracking as tight as possible in order to
 274  * not miss-qualify lock contexts and miss possible deadlocks.
 275  */
 276
 277 static inline bool lockdep_softirq_start(void)
 278 {
 279         bool in_hardirq = false;
 280
 281         if (lockdep_hardirq_context()) {
 282                 in_hardirq = true;
 283                 lockdep_hardirq_exit();
 284         }
 285
 286         lockdep_softirq_enter();
 287
 288         return in_hardirq;
 289 }
 290
 291 static inline void lockdep_softirq_end(bool in_hardirq)
 292 {
 293         lockdep_softirq_exit();
 294
 295         if (in_hardirq)
 296                 lockdep_hardirq_enter();
 297 }
 298 #else
 299 static inline bool lockdep_softirq_start(void) { return false; }
 300 static inline void lockdep_softirq_end(bool in_hardirq) { }
 301 #endif
 302
 303 asmlinkage __visible void __softirq_entry __do_softirq(void)
 304 {
 305         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 306         unsigned long old_flags = current->flags;
 307         int max_restart = MAX_SOFTIRQ_RESTART;
 308         struct softirq_action *h;
 309         bool in_hardirq;
 310         __u32 pending;
 311         int softirq_bit;
 312
 313         /*
 314          * Mask out PF_MEMALLOC as the current task context is borrowed for the
 315          * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
 316          * again if the socket is related to swapping.
 317          */
 318         current->flags &= ~PF_MEMALLOC;
 319
 320         pending = local_softirq_pending();
 321
 322         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 323         in_hardirq = lockdep_softirq_start();
 324         account_softirq_enter(current);
 325
 326 restart:
 327         /* Reset the pending bitmask before enabling irqs */
 328         set_softirq_pending(0);
 329
 330         local_irq_enable();
 331
 332         h = softirq_vec;
 333
 334         while ((softirq_bit = ffs(pending))) {
 335                 unsigned int vec_nr;
 336                 int prev_count;
 337
 338                 h += softirq_bit - 1;
 339
 340                 vec_nr = h - softirq_vec;
 341                 prev_count = preempt_count();
 342
 343                 kstat_incr_softirqs_this_cpu(vec_nr);
 344
 345                 trace_softirq_entry(vec_nr);
 346                 h->action(h);
 347                 trace_softirq_exit(vec_nr);
 348                 if (unlikely(prev_count != preempt_count())) {
 349                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 350                                vec_nr, softirq_to_name[vec_nr], h->action,
 351                                prev_count, preempt_count());
 352                         preempt_count_set(prev_count);
 353                 }
 354                 h++;
 355                 pending >>= softirq_bit;
 356         }
 357
 358         if (__this_cpu_read(ksoftirqd) == current)
 359                 rcu_softirq_qs();
 360         local_irq_disable();
 361
 362         pending = local_softirq_pending();
 363         if (pending) {
 364                 if (time_before(jiffies, end) && !need_resched() &&
 365                     --max_restart)
 366                         goto restart;
 367
 368                 wakeup_softirqd();
 369         }
 370
 371         account_softirq_exit(current);
 372         lockdep_softirq_end(in_hardirq);
 373         __local_bh_enable(SOFTIRQ_OFFSET);
 374         WARN_ON_ONCE(in_interrupt());
 375         current_restore_flags(old_flags, PF_MEMALLOC);
 376 }
 377
 378 /**
 379  * irq_enter_rcu - Enter an interrupt context with RCU watching
 380  */
 381 void irq_enter_rcu(void)
 382 {
 383         __irq_enter_raw();
 384
 385         if (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET))
 386                 tick_irq_enter();
 387
 388         account_hardirq_enter(current);
 389 }
 390
 391 /**
 392  * irq_enter - Enter an interrupt context including RCU update
 393  */
 394 void irq_enter(void)
 395 {
 396         rcu_irq_enter();
 397         irq_enter_rcu();
 398 }
 399
 400 static inline void tick_irq_exit(void)
 401 {
 402 #ifdef CONFIG_NO_HZ_COMMON
 403         int cpu = smp_processor_id();
 404
 405         /* Make sure that timer wheel updates are propagated */
 406         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 407                 if (!in_irq())
 408                         tick_nohz_irq_exit();
 409         }
 410 #endif
 411 }
 412
 413 static inline void __irq_exit_rcu(void)
 414 {
 415 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 416         local_irq_disable();
 417 #else
 418         lockdep_assert_irqs_disabled();
 419 #endif
 420         account_hardirq_exit(current);
 421         preempt_count_sub(HARDIRQ_OFFSET);
 422         if (!in_interrupt() && local_softirq_pending())
 423                 invoke_softirq();
 424
 425         tick_irq_exit();
 426 }
 427
 428 /**
 429  * irq_exit_rcu() - Exit an interrupt context without updating RCU
 430  *
 431  * Also processes softirqs if needed and possible.
 432  */
 433 void irq_exit_rcu(void)
 434 {
 435         __irq_exit_rcu();
 436          /* must be last! */
 437         lockdep_hardirq_exit();
 438 }
 439
 440 /**
 441  * irq_exit - Exit an interrupt context, update RCU and lockdep
 442  *
 443  * Also processes softirqs if needed and possible.
 444  */
 445 void irq_exit(void)
 446 {
 447         __irq_exit_rcu();
 448         rcu_irq_exit();
 449          /* must be last! */
 450         lockdep_hardirq_exit();
 451 }
 452
 453 /*
 454  * This function must run with irqs disabled!
 455  */
 456 inline void raise_softirq_irqoff(unsigned int nr)
 457 {
 458         __raise_softirq_irqoff(nr);
 459
 460         /*
 461          * If we're in an interrupt or softirq, we're done
 462          * (this also catches softirq-disabled code). We will
 463          * actually run the softirq once we return from
 464          * the irq or softirq.
 465          *
 466          * Otherwise we wake up ksoftirqd to make sure we
 467          * schedule the softirq soon.
 468          */
 469         if (!in_interrupt())
 470                 wakeup_softirqd();
 471 }
 472
 473 void raise_softirq(unsigned int nr)
 474 {
 475         unsigned long flags;
 476
 477         local_irq_save(flags);
 478         raise_softirq_irqoff(nr);
 479         local_irq_restore(flags);
 480 }
 481
 482 void __raise_softirq_irqoff(unsigned int nr)
 483 {
 484         lockdep_assert_irqs_disabled();
 485         trace_softirq_raise(nr);
 486         or_softirq_pending(1UL << nr);
 487 }
 488
 489 void open_softirq(int nr, void (*action)(struct softirq_action *))
 490 {
 491         softirq_vec[nr].action = action;
 492 }
 493
 494 /*
 495  * Tasklets
 496  */
 497 struct tasklet_head {
 498         struct tasklet_struct *head;
 499         struct tasklet_struct **tail;
 500 };
 501
 502 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 503 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 504
 505 static void __tasklet_schedule_common(struct tasklet_struct *t,
 506                                       struct tasklet_head __percpu *headp,
 507                                       unsigned int softirq_nr)
 508 {
 509         struct tasklet_head *head;
 510         unsigned long flags;
 511
 512         local_irq_save(flags);
 513         head = this_cpu_ptr(headp);
 514         t->next = NULL;
 515         *head->tail = t;
 516         head->tail = &(t->next);
 517         raise_softirq_irqoff(softirq_nr);
 518         local_irq_restore(flags);
 519 }
 520
 521 void __tasklet_schedule(struct tasklet_struct *t)
 522 {
 523         __tasklet_schedule_common(t, &tasklet_vec,
 524                                   TASKLET_SOFTIRQ);
 525 }
 526 EXPORT_SYMBOL(__tasklet_schedule);
 527
 528 void __tasklet_hi_schedule(struct tasklet_struct *t)
 529 {
 530         __tasklet_schedule_common(t, &tasklet_hi_vec,
 531                                   HI_SOFTIRQ);
 532 }
 533 EXPORT_SYMBOL(__tasklet_hi_schedule);
 534
 535 static bool tasklet_clear_sched(struct tasklet_struct *t)
 536 {
 537         if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
 538                 wake_up_var(&t->state);
 539                 return true;
 540         }
 541
 542         WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
 543                   t->use_callback ? "callback" : "func",
 544                   t->use_callback ? (void *)t->callback : (void *)t->func);
 545
 546         return false;
 547 }
 548
 549 static void tasklet_action_common(struct softirq_action *a,
 550                                   struct tasklet_head *tl_head,
 551                                   unsigned int softirq_nr)
 552 {
 553         struct tasklet_struct *list;
 554
 555         local_irq_disable();
 556         list = tl_head->head;
 557         tl_head->head = NULL;
 558         tl_head->tail = &tl_head->head;
 559         local_irq_enable();
 560
 561         while (list) {
 562                 struct tasklet_struct *t = list;
 563
 564                 list = list->next;
 565
 566                 if (tasklet_trylock(t)) {
 567                         if (!atomic_read(&t->count)) {
 568                                 if (tasklet_clear_sched(t)) {
 569                                         if (t->use_callback)
 570                                                 t->callback(t);
 571                                         else
 572                                                 t->func(t->data);
 573                                 }
 574                                 tasklet_unlock(t);
 575                                 continue;
 576                         }
 577                         tasklet_unlock(t);
 578                 }
 579
 580                 local_irq_disable();
 581                 t->next = NULL;
 582                 *tl_head->tail = t;
 583                 tl_head->tail = &t->next;
 584                 __raise_softirq_irqoff(softirq_nr);
 585                 local_irq_enable();
 586         }
 587 }
 588
 589 static __latent_entropy void tasklet_action(struct softirq_action *a)
 590 {
 591         tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
 592 }
 593
 594 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 595 {
 596         tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
 597 }
 598
 599 void tasklet_setup(struct tasklet_struct *t,
 600                    void (*callback)(struct tasklet_struct *))
 601 {
 602         t->next = NULL;
 603         t->state = 0;
 604         atomic_set(&t->count, 0);
 605         t->callback = callback;
 606         t->use_callback = true;
 607         t->data = 0;
 608 }
 609 EXPORT_SYMBOL(tasklet_setup);
 610
 611 void tasklet_init(struct tasklet_struct *t,
 612                   void (*func)(unsigned long), unsigned long data)
 613 {
 614         t->next = NULL;
 615         t->state = 0;
 616         atomic_set(&t->count, 0);
 617         t->func = func;
 618         t->use_callback = false;
 619         t->data = data;
 620 }
 621 EXPORT_SYMBOL(tasklet_init);
 622
 623 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 624 /*
 625  * Do not use in new code. Waiting for tasklets from atomic contexts is
 626  * error prone and should be avoided.
 627  */
 628 void tasklet_unlock_spin_wait(struct tasklet_struct *t)
 629 {
 630         while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
 631                 if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 632                         /*
 633                          * Prevent a live lock when current preempted soft
 634                          * interrupt processing or prevents ksoftirqd from
 635                          * running. If the tasklet runs on a different CPU
 636                          * then this has no effect other than doing the BH
 637                          * disable/enable dance for nothing.
 638                          */
 639                         local_bh_disable();
 640                         local_bh_enable();
 641                 } else {
 642                         cpu_relax();
 643                 }
 644         }
 645 }
 646 EXPORT_SYMBOL(tasklet_unlock_spin_wait);
 647 #endif
 648
 649 void tasklet_kill(struct tasklet_struct *t)
 650 {
 651         if (in_interrupt())
 652                 pr_notice("Attempt to kill tasklet from interrupt\n");
 653
 654         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
 655                 wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
 656
 657         tasklet_unlock_wait(t);
 658         tasklet_clear_sched(t);
 659 }
 660 EXPORT_SYMBOL(tasklet_kill);
 661
 662 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 663 void tasklet_unlock(struct tasklet_struct *t)
 664 {
 665         smp_mb__before_atomic();
 666         clear_bit(TASKLET_STATE_RUN, &t->state);
 667         smp_mb__after_atomic();
 668         wake_up_var(&t->state);
 669 }
 670 EXPORT_SYMBOL_GPL(tasklet_unlock);
 671
 672 void tasklet_unlock_wait(struct tasklet_struct *t)
 673 {
 674         wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
 675 }
 676 EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
 677 #endif
 678
 679 void __init softirq_init(void)
 680 {
 681         int cpu;
 682
 683         for_each_possible_cpu(cpu) {
 684                 per_cpu(tasklet_vec, cpu).tail =
 685                         &per_cpu(tasklet_vec, cpu).head;
 686                 per_cpu(tasklet_hi_vec, cpu).tail =
 687                         &per_cpu(tasklet_hi_vec, cpu).head;
 688         }
 689
 690         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 691         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 692 }
 693
 694 static int ksoftirqd_should_run(unsigned int cpu)
 695 {
 696         return local_softirq_pending();
 697 }
 698
 699 static void run_ksoftirqd(unsigned int cpu)
 700 {
 701         local_irq_disable();
 702         if (local_softirq_pending()) {
 703                 /*
 704                  * We can safely run softirq on inline stack, as we are not deep
 705                  * in the task stack here.
 706                  */
 707                 __do_softirq();
 708                 local_irq_enable();
 709                 cond_resched();
 710                 return;
 711         }
 712         local_irq_enable();
 713 }
 714
 715 #ifdef CONFIG_HOTPLUG_CPU
 716 static int takeover_tasklets(unsigned int cpu)
 717 {
 718         /* CPU is dead, so no lock needed. */
 719         local_irq_disable();
 720
 721         /* Find end, append list for that CPU. */
 722         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 723                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 724                 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 725                 per_cpu(tasklet_vec, cpu).head = NULL;
 726                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 727         }
 728         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 729
 730         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 731                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 732                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 733                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 734                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 735         }
 736         raise_softirq_irqoff(HI_SOFTIRQ);
 737
 738         local_irq_enable();
 739         return 0;
 740 }
 741 #else
 742 #define takeover_tasklets       NULL
 743 #endif /* CONFIG_HOTPLUG_CPU */
 744
 745 static struct smp_hotplug_thread softirq_threads = {
 746         .store                  = &ksoftirqd,
 747         .thread_should_run      = ksoftirqd_should_run,
 748         .thread_fn              = run_ksoftirqd,
 749         .thread_comm            = "ksoftirqd/%u",
 750 };
 751
 752 static __init int spawn_ksoftirqd(void)
 753 {
 754         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 755                                   takeover_tasklets);
 756         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 757
 758         return 0;
 759 }
 760 early_initcall(spawn_ksoftirqd);
 761
 762 /*
 763  * [ These __weak aliases are kept in a separate compilation unit, so that
 764  *   GCC does not inline them incorrectly. ]
 765  */
 766
 767 int __init __weak early_irq_init(void)
 768 {
 769         return 0;
 770 }
 771
 772 int __init __weak arch_probe_nr_irqs(void)
 773 {
 774         return NR_IRQS_LEGACY;
 775 }
 776
 777 int __init __weak arch_early_irq_init(void)
 778 {
 779         return 0;
 780 }
 781
 782 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 783 {
 784         return from;
 785 }