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 #ifdef CONFIG_NO_HZ
 284         int cpu = smp_processor_id();
 285         if (idle_cpu(cpu) && !in_interrupt())
 286                 tick_nohz_stop_idle(cpu);
 287 #endif
 288         __irq_enter();
 289 #ifdef CONFIG_NO_HZ
 290         if (idle_cpu(cpu))
 291                 tick_nohz_update_jiffies();
 292 #endif
 293 }
 294
 295 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
 296 # define invoke_softirq()       __do_softirq()
 297 #else
 298 # define invoke_softirq()       do_softirq()
 299 #endif
 300
 301 /*
 302  * Exit an interrupt context. Process softirqs if needed and possible:
 303  */
 304 void irq_exit(void)
 305 {
 306         account_system_vtime(current);
 307         trace_hardirq_exit();
 308         sub_preempt_count(IRQ_EXIT_OFFSET);
 309         if (!in_interrupt() && local_softirq_pending())
 310                 invoke_softirq();
 311
 312 #ifdef CONFIG_NO_HZ
 313         /* Make sure that timer wheel updates are propagated */
 314         if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
 315                 tick_nohz_stop_sched_tick();
 316 #endif
 317         preempt_enable_no_resched();
 318 }
 319
 320 /*
 321  * This function must run with irqs disabled!
 322  */
 323 inline void raise_softirq_irqoff(unsigned int nr)
 324 {
 325         __raise_softirq_irqoff(nr);
 326
 327         /*
 328          * If we're in an interrupt or softirq, we're done
 329          * (this also catches softirq-disabled code). We will
 330          * actually run the softirq once we return from
 331          * the irq or softirq.
 332          *
 333          * Otherwise we wake up ksoftirqd to make sure we
 334          * schedule the softirq soon.
 335          */
 336         if (!in_interrupt())
 337                 wakeup_softirqd();
 338 }
 339
 340 void raise_softirq(unsigned int nr)
 341 {
 342         unsigned long flags;
 343
 344         local_irq_save(flags);
 345         raise_softirq_irqoff(nr);
 346         local_irq_restore(flags);
 347 }
 348
 349 void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
 350 {
 351         softirq_vec[nr].data = data;
 352         softirq_vec[nr].action = action;
 353 }
 354
 355 /* Tasklets */
 356 struct tasklet_head
 357 {
 358         struct tasklet_struct *list;
 359 };
 360
 361 /* Some compilers disobey section attribute on statics when not
 362    initialized -- RR */
 363 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
 364 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };
 365
 366 void __tasklet_schedule(struct tasklet_struct *t)
 367 {
 368         unsigned long flags;
 369
 370         local_irq_save(flags);
 371         t->next = __get_cpu_var(tasklet_vec).list;
 372         __get_cpu_var(tasklet_vec).list = t;
 373         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 374         local_irq_restore(flags);
 375 }
 376
 377 EXPORT_SYMBOL(__tasklet_schedule);
 378
 379 void __tasklet_hi_schedule(struct tasklet_struct *t)
 380 {
 381         unsigned long flags;
 382
 383         local_irq_save(flags);
 384         t->next = __get_cpu_var(tasklet_hi_vec).list;
 385         __get_cpu_var(tasklet_hi_vec).list = t;
 386         raise_softirq_irqoff(HI_SOFTIRQ);
 387         local_irq_restore(flags);
 388 }
 389
 390 EXPORT_SYMBOL(__tasklet_hi_schedule);
 391
 392 static void tasklet_action(struct softirq_action *a)
 393 {
 394         struct tasklet_struct *list;
 395
 396         local_irq_disable();
 397         list = __get_cpu_var(tasklet_vec).list;
 398         __get_cpu_var(tasklet_vec).list = NULL;
 399         local_irq_enable();
 400
 401         while (list) {
 402                 struct tasklet_struct *t = list;
 403
 404                 list = list->next;
 405
 406                 if (tasklet_trylock(t)) {
 407                         if (!atomic_read(&t->count)) {
 408                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 409                                         BUG();
 410                                 t->func(t->data);
 411                                 tasklet_unlock(t);
 412                                 continue;
 413                         }
 414                         tasklet_unlock(t);
 415                 }
 416
 417                 local_irq_disable();
 418                 t->next = __get_cpu_var(tasklet_vec).list;
 419                 __get_cpu_var(tasklet_vec).list = t;
 420                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 421                 local_irq_enable();
 422         }
 423 }
 424
 425 static void tasklet_hi_action(struct softirq_action *a)
 426 {
 427         struct tasklet_struct *list;
 428
 429         local_irq_disable();
 430         list = __get_cpu_var(tasklet_hi_vec).list;
 431         __get_cpu_var(tasklet_hi_vec).list = NULL;
 432         local_irq_enable();
 433
 434         while (list) {
 435                 struct tasklet_struct *t = list;
 436
 437                 list = list->next;
 438
 439                 if (tasklet_trylock(t)) {
 440                         if (!atomic_read(&t->count)) {
 441                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 442                                         BUG();
 443                                 t->func(t->data);
 444                                 tasklet_unlock(t);
 445                                 continue;
 446                         }
 447                         tasklet_unlock(t);
 448                 }
 449
 450                 local_irq_disable();
 451                 t->next = __get_cpu_var(tasklet_hi_vec).list;
 452                 __get_cpu_var(tasklet_hi_vec).list = t;
 453                 __raise_softirq_irqoff(HI_SOFTIRQ);
 454                 local_irq_enable();
 455         }
 456 }
 457
 458
 459 void tasklet_init(struct tasklet_struct *t,
 460                   void (*func)(unsigned long), unsigned long data)
 461 {
 462         t->next = NULL;
 463         t->state = 0;
 464         atomic_set(&t->count, 0);
 465         t->func = func;
 466         t->data = data;
 467 }
 468
 469 EXPORT_SYMBOL(tasklet_init);
 470
 471 void tasklet_kill(struct tasklet_struct *t)
 472 {
 473         if (in_interrupt())
 474                 printk("Attempt to kill tasklet from interrupt\n");
 475
 476         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 477                 do
 478                         yield();
 479                 while (test_bit(TASKLET_STATE_SCHED, &t->state));
 480         }
 481         tasklet_unlock_wait(t);
 482         clear_bit(TASKLET_STATE_SCHED, &t->state);
 483 }
 484
 485 EXPORT_SYMBOL(tasklet_kill);
 486
 487 void __init softirq_init(void)
 488 {
 489         open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
 490         open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
 491 }
 492
 493 static int ksoftirqd(void * __bind_cpu)
 494 {
 495         set_current_state(TASK_INTERRUPTIBLE);
 496
 497         while (!kthread_should_stop()) {
 498                 preempt_disable();
 499                 if (!local_softirq_pending()) {
 500                         preempt_enable_no_resched();
 501                         schedule();
 502                         preempt_disable();
 503                 }
 504
 505                 __set_current_state(TASK_RUNNING);
 506
 507                 while (local_softirq_pending()) {
 508                         /* Preempt disable stops cpu going offline.
 509                            If already offline, we'll be on wrong CPU:
 510                            don't process */
 511                         if (cpu_is_offline((long)__bind_cpu))
 512                                 goto wait_to_die;
 513                         do_softirq();
 514                         preempt_enable_no_resched();
 515                         cond_resched();
 516                         preempt_disable();
 517                 }
 518                 preempt_enable();
 519                 set_current_state(TASK_INTERRUPTIBLE);
 520         }
 521         __set_current_state(TASK_RUNNING);
 522         return 0;
 523
 524 wait_to_die:
 525         preempt_enable();
 526         /* Wait for kthread_stop */
 527         set_current_state(TASK_INTERRUPTIBLE);
 528         while (!kthread_should_stop()) {
 529                 schedule();
 530                 set_current_state(TASK_INTERRUPTIBLE);
 531         }
 532         __set_current_state(TASK_RUNNING);
 533         return 0;
 534 }
 535
 536 #ifdef CONFIG_HOTPLUG_CPU
 537 /*
 538  * tasklet_kill_immediate is called to remove a tasklet which can already be
 539  * scheduled for execution on @cpu.
 540  *
 541  * Unlike tasklet_kill, this function removes the tasklet
 542  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 543  *
 544  * When this function is called, @cpu must be in the CPU_DEAD state.
 545  */
 546 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 547 {
 548         struct tasklet_struct **i;
 549
 550         BUG_ON(cpu_online(cpu));
 551         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 552
 553         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 554                 return;
 555
 556         /* CPU is dead, so no lock needed. */
 557         for (i = &per_cpu(tasklet_vec, cpu).list; *i; i = &(*i)->next) {
 558                 if (*i == t) {
 559                         *i = t->next;
 560                         return;
 561                 }
 562         }
 563         BUG();
 564 }
 565
 566 static void takeover_tasklets(unsigned int cpu)
 567 {
 568         struct tasklet_struct **i;
 569
 570         /* CPU is dead, so no lock needed. */
 571         local_irq_disable();
 572
 573         /* Find end, append list for that CPU. */
 574         for (i = &__get_cpu_var(tasklet_vec).list; *i; i = &(*i)->next);
 575         *i = per_cpu(tasklet_vec, cpu).list;
 576         per_cpu(tasklet_vec, cpu).list = NULL;
 577         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 578
 579         for (i = &__get_cpu_var(tasklet_hi_vec).list; *i; i = &(*i)->next);
 580         *i = per_cpu(tasklet_hi_vec, cpu).list;
 581         per_cpu(tasklet_hi_vec, cpu).list = NULL;
 582         raise_softirq_irqoff(HI_SOFTIRQ);
 583
 584         local_irq_enable();
 585 }
 586 #endif /* CONFIG_HOTPLUG_CPU */
 587
 588 static int __cpuinit cpu_callback(struct notifier_block *nfb,
 589                                   unsigned long action,
 590                                   void *hcpu)
 591 {
 592         int hotcpu = (unsigned long)hcpu;
 593         struct task_struct *p;
 594
 595         switch (action) {
 596         case CPU_UP_PREPARE:
 597         case CPU_UP_PREPARE_FROZEN:
 598                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 599                 if (IS_ERR(p)) {
 600                         printk("ksoftirqd for %i failed\n", hotcpu);
 601                         return NOTIFY_BAD;
 602                 }
 603                 kthread_bind(p, hotcpu);
 604                 per_cpu(ksoftirqd, hotcpu) = p;
 605                 break;
 606         case CPU_ONLINE:
 607         case CPU_ONLINE_FROZEN:
 608                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
 609                 break;
 610 #ifdef CONFIG_HOTPLUG_CPU
 611         case CPU_UP_CANCELED:
 612         case CPU_UP_CANCELED_FROZEN:
 613                 if (!per_cpu(ksoftirqd, hotcpu))
 614                         break;
 615                 /* Unbind so it can run.  Fall thru. */
 616                 kthread_bind(per_cpu(ksoftirqd, hotcpu),
 617                              any_online_cpu(cpu_online_map));
 618         case CPU_DEAD:
 619         case CPU_DEAD_FROZEN: {
 620                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 621
 622                 p = per_cpu(ksoftirqd, hotcpu);
 623                 per_cpu(ksoftirqd, hotcpu) = NULL;
 624                 sched_setscheduler(p, SCHED_FIFO, &param);
 625                 kthread_stop(p);
 626                 takeover_tasklets(hotcpu);
 627                 break;
 628         }
 629 #endif /* CONFIG_HOTPLUG_CPU */
 630         }
 631         return NOTIFY_OK;
 632 }
 633
 634 static struct notifier_block __cpuinitdata cpu_nfb = {
 635         .notifier_call = cpu_callback
 636 };
 637
 638 __init int spawn_ksoftirqd(void)
 639 {
 640         void *cpu = (void *)(long)smp_processor_id();
 641         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 642
 643         BUG_ON(err == NOTIFY_BAD);
 644         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 645         register_cpu_notifier(&cpu_nfb);
 646         return 0;
 647 }
 648
 649 #ifdef CONFIG_SMP
 650 /*
 651  * Call a function on all processors
 652  */
 653 int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait)
 654 {
 655         int ret = 0;
 656
 657         preempt_disable();
 658         ret = smp_call_function(func, info, retry, wait);
 659         local_irq_disable();
 660         func(info);
 661         local_irq_enable();
 662         preempt_enable();
 663         return ret;
 664 }
 665 EXPORT_SYMBOL(on_each_cpu);
 666 #endif