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