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 #include <linux/module.h>
  12 #include <linux/kernel_stat.h>
  13 #include <linux/interrupt.h>
  14 #include <linux/init.h>
  15 #include <linux/mm.h>
  16 #include <linux/notifier.h>
  17 #include <linux/percpu.h>
  18 #include <linux/cpu.h>
  19 #include <linux/freezer.h>
  20 #include <linux/kthread.h>
  21 #include <linux/rcupdate.h>
  22 #include <linux/smp.h>
  23 #include <linux/tick.h>
  24
  25 #include <asm/irq.h>
  26 /*
  27    - No shared variables, all the data are CPU local.
  28    - If a softirq needs serialization, let it serialize itself
  29      by its own spinlocks.
  30    - Even if softirq is serialized, only local cpu is marked for
  31      execution. Hence, we get something sort of weak cpu binding.
  32      Though it is still not clear, will it result in better locality
  33      or will not.
  34
  35    Examples:
  36    - NET RX softirq. It is multithreaded and does not require
  37      any global serialization.
  38    - NET TX softirq. It kicks software netdevice queues, hence
  39      it is logically serialized per device, but this serialization
  40      is invisible to common code.
  41    - Tasklets: serialized wrt itself.
  42  */
  43
  44 #ifndef __ARCH_IRQ_STAT
  45 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
  46 EXPORT_SYMBOL(irq_stat);
  47 #endif
  48
  49 static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp;
  50
  51 static DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  52
  53 /*
  54  * we cannot loop indefinitely here to avoid userspace starvation,
  55  * but we also don't want to introduce a worst case 1/HZ latency
  56  * to the pending events, so lets the scheduler to balance
  57  * the softirq load for us.
  58  */
  59 static inline void wakeup_softirqd(void)
  60 {
  61         /* Interrupts are disabled: no need to stop preemption */
  62         struct task_struct *tsk = __get_cpu_var(ksoftirqd);
  63
  64         if (tsk && tsk->state != TASK_RUNNING)
  65                 wake_up_process(tsk);
  66 }
  67
  68 /*
  69  * This one is for softirq.c-internal use,
  70  * where hardirqs are disabled legitimately:
  71  */
  72 #ifdef CONFIG_TRACE_IRQFLAGS
  73 static void __local_bh_disable(unsigned long ip)
  74 {
  75         unsigned long flags;
  76
  77         WARN_ON_ONCE(in_irq());
  78
  79         raw_local_irq_save(flags);
  80         add_preempt_count(SOFTIRQ_OFFSET);
  81         /*
  82          * Were softirqs turned off above:
  83          */
  84         if (softirq_count() == SOFTIRQ_OFFSET)
  85                 trace_softirqs_off(ip);
  86         raw_local_irq_restore(flags);
  87 }
  88 #else /* !CONFIG_TRACE_IRQFLAGS */
  89 static inline void __local_bh_disable(unsigned long ip)
  90 {
  91         add_preempt_count(SOFTIRQ_OFFSET);
  92         barrier();
  93 }
  94 #endif /* CONFIG_TRACE_IRQFLAGS */
  95
  96 void local_bh_disable(void)
  97 {
  98         __local_bh_disable((unsigned long)__builtin_return_address(0));
  99 }
 100
 101 EXPORT_SYMBOL(local_bh_disable);
 102
 103 void __local_bh_enable(void)
 104 {
 105         WARN_ON_ONCE(in_irq());
 106
 107         /*
 108          * softirqs should never be enabled by __local_bh_enable(),
 109          * it always nests inside local_bh_enable() sections:
 110          */
 111         WARN_ON_ONCE(softirq_count() == SOFTIRQ_OFFSET);
 112
 113         sub_preempt_count(SOFTIRQ_OFFSET);
 114 }
 115 EXPORT_SYMBOL_GPL(__local_bh_enable);
 116
 117 /*
 118  * Special-case - softirqs can safely be enabled in
 119  * cond_resched_softirq(), or by __do_softirq(),
 120  * without processing still-pending softirqs:
 121  */
 122 void _local_bh_enable(void)
 123 {
 124         WARN_ON_ONCE(in_irq());
 125         WARN_ON_ONCE(!irqs_disabled());
 126
 127         if (softirq_count() == SOFTIRQ_OFFSET)
 128                 trace_softirqs_on((unsigned long)__builtin_return_address(0));
 129         sub_preempt_count(SOFTIRQ_OFFSET);
 130 }
 131
 132 EXPORT_SYMBOL(_local_bh_enable);
 133
 134 void local_bh_enable(void)
 135 {
 136 #ifdef CONFIG_TRACE_IRQFLAGS
 137         unsigned long flags;
 138
 139         WARN_ON_ONCE(in_irq());
 140 #endif
 141         WARN_ON_ONCE(irqs_disabled());
 142
 143 #ifdef CONFIG_TRACE_IRQFLAGS
 144         local_irq_save(flags);
 145 #endif
 146         /*
 147          * Are softirqs going to be turned on now:
 148          */
 149         if (softirq_count() == SOFTIRQ_OFFSET)
 150                 trace_softirqs_on((unsigned long)__builtin_return_address(0));
 151         /*
 152          * Keep preemption disabled until we are done with
 153          * softirq processing:
 154          */
 155         sub_preempt_count(SOFTIRQ_OFFSET - 1);
 156
 157         if (unlikely(!in_interrupt() && local_softirq_pending()))
 158                 do_softirq();
 159
 160         dec_preempt_count();
 161 #ifdef CONFIG_TRACE_IRQFLAGS
 162         local_irq_restore(flags);
 163 #endif
 164         preempt_check_resched();
 165 }
 166 EXPORT_SYMBOL(local_bh_enable);
 167
 168 void local_bh_enable_ip(unsigned long ip)
 169 {
 170 #ifdef CONFIG_TRACE_IRQFLAGS
 171         unsigned long flags;
 172
 173         WARN_ON_ONCE(in_irq());
 174
 175         local_irq_save(flags);
 176 #endif
 177         /*
 178          * Are softirqs going to be turned on now:
 179          */
 180         if (softirq_count() == SOFTIRQ_OFFSET)
 181                 trace_softirqs_on(ip);
 182         /*
 183          * Keep preemption disabled until we are done with
 184          * softirq processing:
 185          */
 186         sub_preempt_count(SOFTIRQ_OFFSET - 1);
 187
 188         if (unlikely(!in_interrupt() && local_softirq_pending()))
 189                 do_softirq();
 190
 191         dec_preempt_count();
 192 #ifdef CONFIG_TRACE_IRQFLAGS
 193         local_irq_restore(flags);
 194 #endif
 195         preempt_check_resched();
 196 }
 197 EXPORT_SYMBOL(local_bh_enable_ip);
 198
 199 /*
 200  * We restart softirq processing MAX_SOFTIRQ_RESTART times,
 201  * and we fall back to softirqd after that.
 202  *
 203  * This number has been established via experimentation.
 204  * The two things to balance is latency against fairness -
 205  * we want to handle softirqs as soon as possible, but they
 206  * should not be able to lock up the box.
 207  */
 208 #define MAX_SOFTIRQ_RESTART 10
 209
 210 asmlinkage void __do_softirq(void)
 211 {
 212         struct softirq_action *h;
 213         __u32 pending;
 214         int max_restart = MAX_SOFTIRQ_RESTART;
 215         int cpu;
 216
 217         pending = local_softirq_pending();
 218         account_system_vtime(current);
 219
 220         __local_bh_disable((unsigned long)__builtin_return_address(0));
 221         trace_softirq_enter();
 222
 223         cpu = smp_processor_id();
 224 restart:
 225         /* Reset the pending bitmask before enabling irqs */
 226         set_softirq_pending(0);
 227
 228         local_irq_enable();
 229
 230         h = softirq_vec;
 231
 232         do {
 233                 if (pending & 1) {
 234                         h->action(h);
 235                         rcu_bh_qsctr_inc(cpu);
 236                 }
 237                 h++;
 238                 pending >>= 1;
 239         } while (pending);
 240
 241         local_irq_disable();
 242
 243         pending = local_softirq_pending();
 244         if (pending && --max_restart)
 245                 goto restart;
 246
 247         if (pending)
 248                 wakeup_softirqd();
 249
 250         trace_softirq_exit();
 251
 252         account_system_vtime(current);
 253         _local_bh_enable();
 254 }
 255
 256 #ifndef __ARCH_HAS_DO_SOFTIRQ
 257
 258 asmlinkage void do_softirq(void)
 259 {
 260         __u32 pending;
 261         unsigned long flags;
 262
 263         if (in_interrupt())
 264                 return;
 265
 266         local_irq_save(flags);
 267
 268         pending = local_softirq_pending();
 269
 270         if (pending)
 271                 __do_softirq();
 272
 273         local_irq_restore(flags);
 274 }
 275
 276 #endif
 277
 278 /*
 279  * Enter an interrupt context.
 280  */
 281 void irq_enter(void)
 282 {
 283         __irq_enter();
 284 #ifdef CONFIG_NO_HZ
 285         if (idle_cpu(smp_processor_id()))
 286                 tick_nohz_update_jiffies();
 287 #endif
 288 }
 289
 290 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
 291 # define invoke_softirq()       __do_softirq()
 292 #else
 293 # define invoke_softirq()       do_softirq()
 294 #endif
 295
 296 /*
 297  * Exit an interrupt context. Process softirqs if needed and possible:
 298  */
 299 void irq_exit(void)
 300 {
 301         account_system_vtime(current);
 302         trace_hardirq_exit();
 303         sub_preempt_count(IRQ_EXIT_OFFSET);
 304         if (!in_interrupt() && local_softirq_pending())
 305                 invoke_softirq();
 306
 307 #ifdef CONFIG_NO_HZ
 308         /* Make sure that timer wheel updates are propagated */
 309         if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
 310                 tick_nohz_stop_sched_tick();
 311 #endif
 312         preempt_enable_no_resched();
 313 }
 314
 315 /*
 316  * This function must run with irqs disabled!
 317  */
 318 inline fastcall void raise_softirq_irqoff(unsigned int nr)
 319 {
 320         __raise_softirq_irqoff(nr);
 321
 322         /*
 323          * If we're in an interrupt or softirq, we're done
 324          * (this also catches softirq-disabled code). We will
 325          * actually run the softirq once we return from
 326          * the irq or softirq.
 327          *
 328          * Otherwise we wake up ksoftirqd to make sure we
 329          * schedule the softirq soon.
 330          */
 331         if (!in_interrupt())
 332                 wakeup_softirqd();
 333 }
 334
 335 void fastcall raise_softirq(unsigned int nr)
 336 {
 337         unsigned long flags;
 338
 339         local_irq_save(flags);
 340         raise_softirq_irqoff(nr);
 341         local_irq_restore(flags);
 342 }
 343
 344 void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
 345 {
 346         softirq_vec[nr].data = data;
 347         softirq_vec[nr].action = action;
 348 }
 349
 350 /* Tasklets */
 351 struct tasklet_head
 352 {
 353         struct tasklet_struct *list;
 354 };
 355
 356 /* Some compilers disobey section attribute on statics when not
 357    initialized -- RR */
 358 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
 359 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };
 360
 361 void fastcall __tasklet_schedule(struct tasklet_struct *t)
 362 {
 363         unsigned long flags;
 364
 365         local_irq_save(flags);
 366         t->next = __get_cpu_var(tasklet_vec).list;
 367         __get_cpu_var(tasklet_vec).list = t;
 368         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 369         local_irq_restore(flags);
 370 }
 371
 372 EXPORT_SYMBOL(__tasklet_schedule);
 373
 374 void fastcall __tasklet_hi_schedule(struct tasklet_struct *t)
 375 {
 376         unsigned long flags;
 377
 378         local_irq_save(flags);
 379         t->next = __get_cpu_var(tasklet_hi_vec).list;
 380         __get_cpu_var(tasklet_hi_vec).list = t;
 381         raise_softirq_irqoff(HI_SOFTIRQ);
 382         local_irq_restore(flags);
 383 }
 384
 385 EXPORT_SYMBOL(__tasklet_hi_schedule);
 386
 387 static void tasklet_action(struct softirq_action *a)
 388 {
 389         struct tasklet_struct *list;
 390
 391         local_irq_disable();
 392         list = __get_cpu_var(tasklet_vec).list;
 393         __get_cpu_var(tasklet_vec).list = NULL;
 394         local_irq_enable();
 395
 396         while (list) {
 397                 struct tasklet_struct *t = list;
 398
 399                 list = list->next;
 400
 401                 if (tasklet_trylock(t)) {
 402                         if (!atomic_read(&t->count)) {
 403                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 404                                         BUG();
 405                                 t->func(t->data);
 406                                 tasklet_unlock(t);
 407                                 continue;
 408                         }
 409                         tasklet_unlock(t);
 410                 }
 411
 412                 local_irq_disable();
 413                 t->next = __get_cpu_var(tasklet_vec).list;
 414                 __get_cpu_var(tasklet_vec).list = t;
 415                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 416                 local_irq_enable();
 417         }
 418 }
 419
 420 static void tasklet_hi_action(struct softirq_action *a)
 421 {
 422         struct tasklet_struct *list;
 423
 424         local_irq_disable();
 425         list = __get_cpu_var(tasklet_hi_vec).list;
 426         __get_cpu_var(tasklet_hi_vec).list = NULL;
 427         local_irq_enable();
 428
 429         while (list) {
 430                 struct tasklet_struct *t = list;
 431
 432                 list = list->next;
 433
 434                 if (tasklet_trylock(t)) {
 435                         if (!atomic_read(&t->count)) {
 436                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 437                                         BUG();
 438                                 t->func(t->data);
 439                                 tasklet_unlock(t);
 440                                 continue;
 441                         }
 442                         tasklet_unlock(t);
 443                 }
 444
 445                 local_irq_disable();
 446                 t->next = __get_cpu_var(tasklet_hi_vec).list;
 447                 __get_cpu_var(tasklet_hi_vec).list = t;
 448                 __raise_softirq_irqoff(HI_SOFTIRQ);
 449                 local_irq_enable();
 450         }
 451 }
 452
 453
 454 void tasklet_init(struct tasklet_struct *t,
 455                   void (*func)(unsigned long), unsigned long data)
 456 {
 457         t->next = NULL;
 458         t->state = 0;
 459         atomic_set(&t->count, 0);
 460         t->func = func;
 461         t->data = data;
 462 }
 463
 464 EXPORT_SYMBOL(tasklet_init);
 465
 466 void tasklet_kill(struct tasklet_struct *t)
 467 {
 468         if (in_interrupt())
 469                 printk("Attempt to kill tasklet from interrupt\n");
 470
 471         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 472                 do
 473                         yield();
 474                 while (test_bit(TASKLET_STATE_SCHED, &t->state));
 475         }
 476         tasklet_unlock_wait(t);
 477         clear_bit(TASKLET_STATE_SCHED, &t->state);
 478 }
 479
 480 EXPORT_SYMBOL(tasklet_kill);
 481
 482 void __init softirq_init(void)
 483 {
 484         open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
 485         open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
 486 }
 487
 488 static int ksoftirqd(void * __bind_cpu)
 489 {
 490         set_current_state(TASK_INTERRUPTIBLE);
 491
 492         while (!kthread_should_stop()) {
 493                 preempt_disable();
 494                 if (!local_softirq_pending()) {
 495                         preempt_enable_no_resched();
 496                         schedule();
 497                         preempt_disable();
 498                 }
 499
 500                 __set_current_state(TASK_RUNNING);
 501
 502                 while (local_softirq_pending()) {
 503                         /* Preempt disable stops cpu going offline.
 504                            If already offline, we'll be on wrong CPU:
 505                            don't process */
 506                         if (cpu_is_offline((long)__bind_cpu))
 507                                 goto wait_to_die;
 508                         do_softirq();
 509                         preempt_enable_no_resched();
 510                         cond_resched();
 511                         preempt_disable();
 512                 }
 513                 preempt_enable();
 514                 set_current_state(TASK_INTERRUPTIBLE);
 515         }
 516         __set_current_state(TASK_RUNNING);
 517         return 0;
 518
 519 wait_to_die:
 520         preempt_enable();
 521         /* Wait for kthread_stop */
 522         set_current_state(TASK_INTERRUPTIBLE);
 523         while (!kthread_should_stop()) {
 524                 schedule();
 525                 set_current_state(TASK_INTERRUPTIBLE);
 526         }
 527         __set_current_state(TASK_RUNNING);
 528         return 0;
 529 }
 530
 531 #ifdef CONFIG_HOTPLUG_CPU
 532 /*
 533  * tasklet_kill_immediate is called to remove a tasklet which can already be
 534  * scheduled for execution on @cpu.
 535  *
 536  * Unlike tasklet_kill, this function removes the tasklet
 537  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 538  *
 539  * When this function is called, @cpu must be in the CPU_DEAD state.
 540  */
 541 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 542 {
 543         struct tasklet_struct **i;
 544
 545         BUG_ON(cpu_online(cpu));
 546         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 547
 548         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 549                 return;
 550
 551         /* CPU is dead, so no lock needed. */
 552         for (i = &per_cpu(tasklet_vec, cpu).list; *i; i = &(*i)->next) {
 553                 if (*i == t) {
 554                         *i = t->next;
 555                         return;
 556                 }
 557         }
 558         BUG();
 559 }
 560
 561 static void takeover_tasklets(unsigned int cpu)
 562 {
 563         struct tasklet_struct **i;
 564
 565         /* CPU is dead, so no lock needed. */
 566         local_irq_disable();
 567
 568         /* Find end, append list for that CPU. */
 569         for (i = &__get_cpu_var(tasklet_vec).list; *i; i = &(*i)->next);
 570         *i = per_cpu(tasklet_vec, cpu).list;
 571         per_cpu(tasklet_vec, cpu).list = NULL;
 572         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 573
 574         for (i = &__get_cpu_var(tasklet_hi_vec).list; *i; i = &(*i)->next);
 575         *i = per_cpu(tasklet_hi_vec, cpu).list;
 576         per_cpu(tasklet_hi_vec, cpu).list = NULL;
 577         raise_softirq_irqoff(HI_SOFTIRQ);
 578
 579         local_irq_enable();
 580 }
 581 #endif /* CONFIG_HOTPLUG_CPU */
 582
 583 static int __cpuinit cpu_callback(struct notifier_block *nfb,
 584                                   unsigned long action,
 585                                   void *hcpu)
 586 {
 587         int hotcpu = (unsigned long)hcpu;
 588         struct task_struct *p;
 589
 590         switch (action) {
 591         case CPU_UP_PREPARE:
 592         case CPU_UP_PREPARE_FROZEN:
 593                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 594                 if (IS_ERR(p)) {
 595                         printk("ksoftirqd for %i failed\n", hotcpu);
 596                         return NOTIFY_BAD;
 597                 }
 598                 kthread_bind(p, hotcpu);
 599                 per_cpu(ksoftirqd, hotcpu) = p;
 600                 break;
 601         case CPU_ONLINE:
 602         case CPU_ONLINE_FROZEN:
 603                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
 604                 break;
 605 #ifdef CONFIG_HOTPLUG_CPU
 606         case CPU_UP_CANCELED:
 607         case CPU_UP_CANCELED_FROZEN:
 608                 if (!per_cpu(ksoftirqd, hotcpu))
 609                         break;
 610                 /* Unbind so it can run.  Fall thru. */
 611                 kthread_bind(per_cpu(ksoftirqd, hotcpu),
 612                              any_online_cpu(cpu_online_map));
 613         case CPU_DEAD:
 614         case CPU_DEAD_FROZEN: {
 615                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 616
 617                 p = per_cpu(ksoftirqd, hotcpu);
 618                 per_cpu(ksoftirqd, hotcpu) = NULL;
 619                 sched_setscheduler(p, SCHED_FIFO, &param);
 620                 kthread_stop(p);
 621                 takeover_tasklets(hotcpu);
 622                 break;
 623         }
 624 #endif /* CONFIG_HOTPLUG_CPU */
 625         }
 626         return NOTIFY_OK;
 627 }
 628
 629 static struct notifier_block __cpuinitdata cpu_nfb = {
 630         .notifier_call = cpu_callback
 631 };
 632
 633 __init int spawn_ksoftirqd(void)
 634 {
 635         void *cpu = (void *)(long)smp_processor_id();
 636         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 637
 638         BUG_ON(err == NOTIFY_BAD);
 639         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 640         register_cpu_notifier(&cpu_nfb);
 641         return 0;
 642 }
 643
 644 #ifdef CONFIG_SMP
 645 /*
 646  * Call a function on all processors
 647  */
 648 int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait)
 649 {
 650         int ret = 0;
 651
 652         preempt_disable();
 653         ret = smp_call_function(func, info, retry, wait);
 654         local_irq_disable();
 655         func(info);
 656         local_irq_enable();
 657         preempt_enable();
 658         return ret;
 659 }
 660 EXPORT_SYMBOL(on_each_cpu);
 661 #endif