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 /*
  61  * active_softirqs -- per cpu, a mask of softirqs that are being handled,
  62  * with the expectation that approximate answers are acceptable and therefore
  63  * no synchronization.
  64  */
  65 DEFINE_PER_CPU(__u32, active_softirqs);
  66
  67 const char * const softirq_to_name[NR_SOFTIRQS] = {
  68         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
  69         "TASKLET", "SCHED", "HRTIMER", "RCU"
  70 };
  71
  72 /*
  73  * we cannot loop indefinitely here to avoid userspace starvation,
  74  * but we also don't want to introduce a worst case 1/HZ latency
  75  * to the pending events, so lets the scheduler to balance
  76  * the softirq load for us.
  77  */
  78 static void wakeup_softirqd(void)
  79 {
  80         /* Interrupts are disabled: no need to stop preemption */
  81         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  82
  83         if (tsk && tsk->state != TASK_RUNNING)
  84                 wake_up_process(tsk);
  85 }
  86
  87 /*
  88  * preempt_count and SOFTIRQ_OFFSET usage:
  89  * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
  90  *   softirq processing.
  91  * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
  92  *   on local_bh_disable or local_bh_enable.
  93  * This lets us distinguish between whether we are currently processing
  94  * softirq and whether we just have bh disabled.
  95  */
  96
  97 /*
  98  * This one is for softirq.c-internal use,
  99  * where hardirqs are disabled legitimately:
 100  */
 101 #ifdef CONFIG_TRACE_IRQFLAGS
 102 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 103 {
 104         unsigned long flags;
 105
 106         WARN_ON_ONCE(in_irq());
 107
 108         raw_local_irq_save(flags);
 109         /*
 110          * The preempt tracer hooks into preempt_count_add and will break
 111          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 112          * is set and before current->softirq_enabled is cleared.
 113          * We must manually increment preempt_count here and manually
 114          * call the trace_preempt_off later.
 115          */
 116         __preempt_count_add(cnt);
 117         /*
 118          * Were softirqs turned off above:
 119          */
 120         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 121                 trace_softirqs_off(ip);
 122         raw_local_irq_restore(flags);
 123
 124         if (preempt_count() == cnt) {
 125 #ifdef CONFIG_DEBUG_PREEMPT
 126                 current->preempt_disable_ip = get_parent_ip(CALLER_ADDR1);
 127 #endif
 128                 trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
 129         }
 130 }
 131 EXPORT_SYMBOL(__local_bh_disable_ip);
 132 #endif /* CONFIG_TRACE_IRQFLAGS */
 133
 134 static void __local_bh_enable(unsigned int cnt)
 135 {
 136         WARN_ON_ONCE(!irqs_disabled());
 137
 138         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 139                 trace_softirqs_on(_RET_IP_);
 140         preempt_count_sub(cnt);
 141 }
 142
 143 /*
 144  * Special-case - softirqs can safely be enabled in
 145  * cond_resched_softirq(), or by __do_softirq(),
 146  * without processing still-pending softirqs:
 147  */
 148 void _local_bh_enable(void)
 149 {
 150         WARN_ON_ONCE(in_irq());
 151         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 152 }
 153 EXPORT_SYMBOL(_local_bh_enable);
 154
 155 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 156 {
 157         WARN_ON_ONCE(in_irq() || irqs_disabled());
 158 #ifdef CONFIG_TRACE_IRQFLAGS
 159         local_irq_disable();
 160 #endif
 161         /*
 162          * Are softirqs going to be turned on now:
 163          */
 164         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 165                 trace_softirqs_on(ip);
 166         /*
 167          * Keep preemption disabled until we are done with
 168          * softirq processing:
 169          */
 170         preempt_count_sub(cnt - 1);
 171
 172         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 173                 /*
 174                  * Run softirq if any pending. And do it in its own stack
 175                  * as we may be calling this deep in a task call stack already.
 176                  */
 177                 do_softirq();
 178         }
 179
 180         preempt_count_dec();
 181 #ifdef CONFIG_TRACE_IRQFLAGS
 182         local_irq_enable();
 183 #endif
 184         preempt_check_resched();
 185 }
 186 EXPORT_SYMBOL(__local_bh_enable_ip);
 187
 188 /*
 189  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 190  * but break the loop if need_resched() is set or after 2 ms.
 191  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 192  * certain cases, such as stop_machine(), jiffies may cease to
 193  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 194  * well to make sure we eventually return from this method.
 195  *
 196  * These limits have been established via experimentation.
 197  * The two things to balance is latency against fairness -
 198  * we want to handle softirqs as soon as possible, but they
 199  * should not be able to lock up the box.
 200  */
 201 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 202 #define MAX_SOFTIRQ_RESTART 10
 203
 204 #ifdef CONFIG_TRACE_IRQFLAGS
 205 /*
 206  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 207  * to keep the lockdep irq context tracking as tight as possible in order to
 208  * not miss-qualify lock contexts and miss possible deadlocks.
 209  */
 210
 211 static inline bool lockdep_softirq_start(void)
 212 {
 213         bool in_hardirq = false;
 214
 215         if (trace_hardirq_context(current)) {
 216                 in_hardirq = true;
 217                 trace_hardirq_exit();
 218         }
 219
 220         lockdep_softirq_enter();
 221
 222         return in_hardirq;
 223 }
 224
 225 static inline void lockdep_softirq_end(bool in_hardirq)
 226 {
 227         lockdep_softirq_exit();
 228
 229         if (in_hardirq)
 230                 trace_hardirq_enter();
 231 }
 232 #else
 233 static inline bool lockdep_softirq_start(void) { return false; }
 234 static inline void lockdep_softirq_end(bool in_hardirq) { }
 235 #endif
 236
 237 #define softirq_deferred_for_rt(pending)                \
 238 ({                                                      \
 239         __u32 deferred = 0;                             \
 240         if (cpupri_check_rt()) {                        \
 241                 deferred = pending & LONG_SOFTIRQ_MASK; \
 242                 pending &= ~LONG_SOFTIRQ_MASK;          \
 243         }                                               \
 244         deferred;                                       \
 245 })
 246
 247 asmlinkage __visible void __softirq_entry __do_softirq(void)
 248 {
 249         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 250         unsigned long old_flags = current->flags;
 251         int max_restart = MAX_SOFTIRQ_RESTART;
 252         struct softirq_action *h;
 253         bool in_hardirq;
 254         __u32 deferred;
 255         __u32 pending;
 256         int softirq_bit;
 257
 258         /*
 259          * Mask out PF_MEMALLOC s current task context is borrowed for the
 260          * softirq. A softirq handled such as network RX might set PF_MEMALLOC
 261          * again if the socket is related to swap
 262          */
 263         current->flags &= ~PF_MEMALLOC;
 264
 265         pending = local_softirq_pending();
 266         deferred = softirq_deferred_for_rt(pending);
 267         account_irq_enter_time(current);
 268         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 269         in_hardirq = lockdep_softirq_start();
 270
 271 restart:
 272         /* Reset the pending bitmask before enabling irqs */
 273         set_softirq_pending(deferred);
 274         __this_cpu_write(active_softirqs, pending);
 275
 276         local_irq_enable();
 277
 278         h = softirq_vec;
 279
 280         while ((softirq_bit = ffs(pending))) {
 281                 unsigned int vec_nr;
 282                 int prev_count;
 283
 284                 h += softirq_bit - 1;
 285
 286                 vec_nr = h - softirq_vec;
 287                 prev_count = preempt_count();
 288
 289                 kstat_incr_softirqs_this_cpu(vec_nr);
 290
 291                 trace_softirq_entry(vec_nr);
 292                 h->action(h);
 293                 trace_softirq_exit(vec_nr);
 294                 if (unlikely(prev_count != preempt_count())) {
 295                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 296                                vec_nr, softirq_to_name[vec_nr], h->action,
 297                                prev_count, preempt_count());
 298                         preempt_count_set(prev_count);
 299                 }
 300                 h++;
 301                 pending >>= softirq_bit;
 302         }
 303
 304         __this_cpu_write(active_softirqs, 0);
 305         rcu_bh_qs();
 306         local_irq_disable();
 307
 308         pending = local_softirq_pending();
 309         deferred = softirq_deferred_for_rt(pending);
 310
 311         if (pending) {
 312                 if (time_before(jiffies, end) && !need_resched() &&
 313                     --max_restart)
 314                         goto restart;
 315         }
 316
 317         if (pending | deferred)
 318                 wakeup_softirqd();
 319         lockdep_softirq_end(in_hardirq);
 320         account_irq_exit_time(current);
 321         __local_bh_enable(SOFTIRQ_OFFSET);
 322         WARN_ON_ONCE(in_interrupt());
 323         tsk_restore_flags(current, old_flags, PF_MEMALLOC);
 324 }
 325
 326 asmlinkage __visible void do_softirq(void)
 327 {
 328         __u32 pending;
 329         unsigned long flags;
 330
 331         if (in_interrupt())
 332                 return;
 333
 334         local_irq_save(flags);
 335
 336         pending = local_softirq_pending();
 337
 338         if (pending)
 339                 do_softirq_own_stack();
 340
 341         local_irq_restore(flags);
 342 }
 343
 344 /*
 345  * Enter an interrupt context.
 346  */
 347 void irq_enter(void)
 348 {
 349         rcu_irq_enter();
 350         if (is_idle_task(current) && !in_interrupt()) {
 351                 /*
 352                  * Prevent raise_softirq from needlessly waking up ksoftirqd
 353                  * here, as softirq will be serviced on return from interrupt.
 354                  */
 355                 local_bh_disable();
 356                 tick_irq_enter();
 357                 _local_bh_enable();
 358         }
 359
 360         __irq_enter();
 361 }
 362
 363 static inline void invoke_softirq(void)
 364 {
 365         if (!force_irqthreads) {
 366 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 367                 /*
 368                  * We can safely execute softirq on the current stack if
 369                  * it is the irq stack, because it should be near empty
 370                  * at this stage.
 371                  */
 372                 __do_softirq();
 373 #else
 374                 /*
 375                  * Otherwise, irq_exit() is called on the task stack that can
 376                  * be potentially deep already. So call softirq in its own stack
 377                  * to prevent from any overrun.
 378                  */
 379                 do_softirq_own_stack();
 380 #endif
 381         } else {
 382                 wakeup_softirqd();
 383         }
 384 }
 385
 386 static inline void tick_irq_exit(void)
 387 {
 388 #ifdef CONFIG_NO_HZ_COMMON
 389         int cpu = smp_processor_id();
 390
 391         /* Make sure that timer wheel updates are propagated */
 392         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 393                 if (!in_interrupt())
 394                         tick_nohz_irq_exit();
 395         }
 396 #endif
 397 }
 398
 399 /*
 400  * Exit an interrupt context. Process softirqs if needed and possible:
 401  */
 402 void irq_exit(void)
 403 {
 404 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 405         local_irq_disable();
 406 #else
 407         WARN_ON_ONCE(!irqs_disabled());
 408 #endif
 409
 410         account_irq_exit_time(current);
 411         preempt_count_sub(HARDIRQ_OFFSET);
 412         if (!in_interrupt() && local_softirq_pending())
 413                 invoke_softirq();
 414
 415         tick_irq_exit();
 416         rcu_irq_exit();
 417         trace_hardirq_exit(); /* must be last! */
 418 }
 419
 420 /*
 421  * This function must run with irqs disabled!
 422  */
 423 inline void raise_softirq_irqoff(unsigned int nr)
 424 {
 425         __raise_softirq_irqoff(nr);
 426
 427         /*
 428          * If we're in an interrupt or softirq, we're done
 429          * (this also catches softirq-disabled code). We will
 430          * actually run the softirq once we return from
 431          * the irq or softirq.
 432          *
 433          * Otherwise we wake up ksoftirqd to make sure we
 434          * schedule the softirq soon.
 435          */
 436         if (!in_interrupt())
 437                 wakeup_softirqd();
 438 }
 439
 440 void raise_softirq(unsigned int nr)
 441 {
 442         unsigned long flags;
 443
 444         local_irq_save(flags);
 445         raise_softirq_irqoff(nr);
 446         local_irq_restore(flags);
 447 }
 448
 449 void __raise_softirq_irqoff(unsigned int nr)
 450 {
 451         trace_softirq_raise(nr);
 452         or_softirq_pending(1UL << nr);
 453 }
 454
 455 void open_softirq(int nr, void (*action)(struct softirq_action *))
 456 {
 457         softirq_vec[nr].action = action;
 458 }
 459
 460 /*
 461  * Tasklets
 462  */
 463 struct tasklet_head {
 464         struct tasklet_struct *head;
 465         struct tasklet_struct **tail;
 466 };
 467
 468 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 469 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 470
 471 void __tasklet_schedule(struct tasklet_struct *t)
 472 {
 473         unsigned long flags;
 474
 475         local_irq_save(flags);
 476         t->next = NULL;
 477         *__this_cpu_read(tasklet_vec.tail) = t;
 478         __this_cpu_write(tasklet_vec.tail, &(t->next));
 479         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 480         local_irq_restore(flags);
 481 }
 482 EXPORT_SYMBOL(__tasklet_schedule);
 483
 484 void __tasklet_hi_schedule(struct tasklet_struct *t)
 485 {
 486         unsigned long flags;
 487
 488         local_irq_save(flags);
 489         t->next = NULL;
 490         *__this_cpu_read(tasklet_hi_vec.tail) = t;
 491         __this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
 492         raise_softirq_irqoff(HI_SOFTIRQ);
 493         local_irq_restore(flags);
 494 }
 495 EXPORT_SYMBOL(__tasklet_hi_schedule);
 496
 497 void __tasklet_hi_schedule_first(struct tasklet_struct *t)
 498 {
 499         BUG_ON(!irqs_disabled());
 500
 501         t->next = __this_cpu_read(tasklet_hi_vec.head);
 502         __this_cpu_write(tasklet_hi_vec.head, t);
 503         __raise_softirq_irqoff(HI_SOFTIRQ);
 504 }
 505 EXPORT_SYMBOL(__tasklet_hi_schedule_first);
 506
 507 static void tasklet_action(struct softirq_action *a)
 508 {
 509         struct tasklet_struct *list;
 510
 511         local_irq_disable();
 512         list = __this_cpu_read(tasklet_vec.head);
 513         __this_cpu_write(tasklet_vec.head, NULL);
 514         __this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
 515         local_irq_enable();
 516
 517         while (list) {
 518                 struct tasklet_struct *t = list;
 519
 520                 list = list->next;
 521
 522                 if (tasklet_trylock(t)) {
 523                         if (!atomic_read(&t->count)) {
 524                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 525                                                         &t->state))
 526                                         BUG();
 527                                 t->func(t->data);
 528                                 tasklet_unlock(t);
 529                                 continue;
 530                         }
 531                         tasklet_unlock(t);
 532                 }
 533
 534                 local_irq_disable();
 535                 t->next = NULL;
 536                 *__this_cpu_read(tasklet_vec.tail) = t;
 537                 __this_cpu_write(tasklet_vec.tail, &(t->next));
 538                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 539                 local_irq_enable();
 540         }
 541 }
 542
 543 static void tasklet_hi_action(struct softirq_action *a)
 544 {
 545         struct tasklet_struct *list;
 546
 547         local_irq_disable();
 548         list = __this_cpu_read(tasklet_hi_vec.head);
 549         __this_cpu_write(tasklet_hi_vec.head, NULL);
 550         __this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
 551         local_irq_enable();
 552
 553         while (list) {
 554                 struct tasklet_struct *t = list;
 555
 556                 list = list->next;
 557
 558                 if (tasklet_trylock(t)) {
 559                         if (!atomic_read(&t->count)) {
 560                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 561                                                         &t->state))
 562                                         BUG();
 563                                 t->func(t->data);
 564                                 tasklet_unlock(t);
 565                                 continue;
 566                         }
 567                         tasklet_unlock(t);
 568                 }
 569
 570                 local_irq_disable();
 571                 t->next = NULL;
 572                 *__this_cpu_read(tasklet_hi_vec.tail) = t;
 573                 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
 574                 __raise_softirq_irqoff(HI_SOFTIRQ);
 575                 local_irq_enable();
 576         }
 577 }
 578
 579 void tasklet_init(struct tasklet_struct *t,
 580                   void (*func)(unsigned long), unsigned long data)
 581 {
 582         t->next = NULL;
 583         t->state = 0;
 584         atomic_set(&t->count, 0);
 585         t->func = func;
 586         t->data = data;
 587 }
 588 EXPORT_SYMBOL(tasklet_init);
 589
 590 void tasklet_kill(struct tasklet_struct *t)
 591 {
 592         if (in_interrupt())
 593                 pr_notice("Attempt to kill tasklet from interrupt\n");
 594
 595         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 596                 do {
 597                         yield();
 598                 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
 599         }
 600         tasklet_unlock_wait(t);
 601         clear_bit(TASKLET_STATE_SCHED, &t->state);
 602 }
 603 EXPORT_SYMBOL(tasklet_kill);
 604
 605 /*
 606  * tasklet_hrtimer
 607  */
 608
 609 /*
 610  * The trampoline is called when the hrtimer expires. It schedules a tasklet
 611  * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
 612  * hrtimer callback, but from softirq context.
 613  */
 614 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
 615 {
 616         struct tasklet_hrtimer *ttimer =
 617                 container_of(timer, struct tasklet_hrtimer, timer);
 618
 619         tasklet_hi_schedule(&ttimer->tasklet);
 620         return HRTIMER_NORESTART;
 621 }
 622
 623 /*
 624  * Helper function which calls the hrtimer callback from
 625  * tasklet/softirq context
 626  */
 627 static void __tasklet_hrtimer_trampoline(unsigned long data)
 628 {
 629         struct tasklet_hrtimer *ttimer = (void *)data;
 630         enum hrtimer_restart restart;
 631
 632         restart = ttimer->function(&ttimer->timer);
 633         if (restart != HRTIMER_NORESTART)
 634                 hrtimer_restart(&ttimer->timer);
 635 }
 636
 637 /**
 638  * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
 639  * @ttimer:      tasklet_hrtimer which is initialized
 640  * @function:    hrtimer callback function which gets called from softirq context
 641  * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
 642  * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
 643  */
 644 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
 645                           enum hrtimer_restart (*function)(struct hrtimer *),
 646                           clockid_t which_clock, enum hrtimer_mode mode)
 647 {
 648         hrtimer_init(&ttimer->timer, which_clock, mode);
 649         ttimer->timer.function = __hrtimer_tasklet_trampoline;
 650         tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
 651                      (unsigned long)ttimer);
 652         ttimer->function = function;
 653 }
 654 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
 655
 656 void __init softirq_init(void)
 657 {
 658         int cpu;
 659
 660         for_each_possible_cpu(cpu) {
 661                 per_cpu(tasklet_vec, cpu).tail =
 662                         &per_cpu(tasklet_vec, cpu).head;
 663                 per_cpu(tasklet_hi_vec, cpu).tail =
 664                         &per_cpu(tasklet_hi_vec, cpu).head;
 665         }
 666
 667         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 668         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 669 }
 670
 671 static int ksoftirqd_should_run(unsigned int cpu)
 672 {
 673         return local_softirq_pending();
 674 }
 675
 676 static void run_ksoftirqd(unsigned int cpu)
 677 {
 678         local_irq_disable();
 679         if (local_softirq_pending()) {
 680                 /*
 681                  * We can safely run softirq on inline stack, as we are not deep
 682                  * in the task stack here.
 683                  */
 684                 __do_softirq();
 685                 local_irq_enable();
 686                 cond_resched_rcu_qs();
 687                 return;
 688         }
 689         local_irq_enable();
 690 }
 691
 692 #ifdef CONFIG_HOTPLUG_CPU
 693 /*
 694  * tasklet_kill_immediate is called to remove a tasklet which can already be
 695  * scheduled for execution on @cpu.
 696  *
 697  * Unlike tasklet_kill, this function removes the tasklet
 698  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 699  *
 700  * When this function is called, @cpu must be in the CPU_DEAD state.
 701  */
 702 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 703 {
 704         struct tasklet_struct **i;
 705
 706         BUG_ON(cpu_online(cpu));
 707         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 708
 709         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 710                 return;
 711
 712         /* CPU is dead, so no lock needed. */
 713         for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 714                 if (*i == t) {
 715                         *i = t->next;
 716                         /* If this was the tail element, move the tail ptr */
 717                         if (*i == NULL)
 718                                 per_cpu(tasklet_vec, cpu).tail = i;
 719                         return;
 720                 }
 721         }
 722         BUG();
 723 }
 724
 725 static void takeover_tasklets(unsigned int cpu)
 726 {
 727         /* CPU is dead, so no lock needed. */
 728         local_irq_disable();
 729
 730         /* Find end, append list for that CPU. */
 731         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 732                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 733                 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 734                 per_cpu(tasklet_vec, cpu).head = NULL;
 735                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 736         }
 737         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 738
 739         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 740                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 741                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 742                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 743                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 744         }
 745         raise_softirq_irqoff(HI_SOFTIRQ);
 746
 747         local_irq_enable();
 748 }
 749 #endif /* CONFIG_HOTPLUG_CPU */
 750
 751 static int cpu_callback(struct notifier_block *nfb, unsigned long action,
 752                         void *hcpu)
 753 {
 754         switch (action) {
 755 #ifdef CONFIG_HOTPLUG_CPU
 756         case CPU_DEAD:
 757         case CPU_DEAD_FROZEN:
 758                 takeover_tasklets((unsigned long)hcpu);
 759                 break;
 760 #endif /* CONFIG_HOTPLUG_CPU */
 761         }
 762         return NOTIFY_OK;
 763 }
 764
 765 static struct notifier_block cpu_nfb = {
 766         .notifier_call = cpu_callback
 767 };
 768
 769 static struct smp_hotplug_thread softirq_threads = {
 770         .store                  = &ksoftirqd,
 771         .thread_should_run      = ksoftirqd_should_run,
 772         .thread_fn              = run_ksoftirqd,
 773         .thread_comm            = "ksoftirqd/%u",
 774 };
 775
 776 static __init int spawn_ksoftirqd(void)
 777 {
 778         register_cpu_notifier(&cpu_nfb);
 779
 780         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 781
 782         return 0;
 783 }
 784 early_initcall(spawn_ksoftirqd);
 785
 786 /*
 787  * [ These __weak aliases are kept in a separate compilation unit, so that
 788  *   GCC does not inline them incorrectly. ]
 789  */
 790
 791 int __init __weak early_irq_init(void)
 792 {
 793         return 0;
 794 }
 795
 796 int __init __weak arch_probe_nr_irqs(void)
 797 {
 798         return NR_IRQS_LEGACY;
 799 }
 800
 801 int __init __weak arch_early_irq_init(void)
 802 {
 803         return 0;
 804 }
 805
 806 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 807 {
 808         return from;
 809 }