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