kernel/softirq.c

   1 /*
   2  *      linux/kernel/softirq.c
   3  *
   4  *      Copyright (C) 1992 Linus Torvalds
   5  *
   6  * Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/kernel_stat.h>
  11 #include <linux/interrupt.h>
  12 #include <linux/init.h>
  13 #include <linux/mm.h>
  14 #include <linux/notifier.h>
  15 #include <linux/percpu.h>
  16 #include <linux/cpu.h>
  17 #include <linux/kthread.h>
  18 #include <linux/rcupdate.h>
  19
  20 #include <asm/irq.h>
  21 /*
  22    - No shared variables, all the data are CPU local.
  23    - If a softirq needs serialization, let it serialize itself
  24      by its own spinlocks.
  25    - Even if softirq is serialized, only local cpu is marked for
  26      execution. Hence, we get something sort of weak cpu binding.
  27      Though it is still not clear, will it result in better locality
  28      or will not.
  29
  30    Examples:
  31    - NET RX softirq. It is multithreaded and does not require
  32      any global serialization.
  33    - NET TX softirq. It kicks software netdevice queues, hence
  34      it is logically serialized per device, but this serialization
  35      is invisible to common code.
  36    - Tasklets: serialized wrt itself.
  37  */
  38
  39 #ifndef __ARCH_IRQ_STAT
  40 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
  41 EXPORT_SYMBOL(irq_stat);
  42 #endif
  43
  44 static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp;
  45
  46 static DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  47
  48 /*
  49  * we cannot loop indefinitely here to avoid userspace starvation,
  50  * but we also don't want to introduce a worst case 1/HZ latency
  51  * to the pending events, so lets the scheduler to balance
  52  * the softirq load for us.
  53  */
  54 static inline void wakeup_softirqd(void)
  55 {
  56         /* Interrupts are disabled: no need to stop preemption */
  57         struct task_struct *tsk = __get_cpu_var(ksoftirqd);
  58
  59         if (tsk && tsk->state != TASK_RUNNING)
  60                 wake_up_process(tsk);
  61 }
  62
  63 /*
  64  * We restart softirq processing MAX_SOFTIRQ_RESTART times,
  65  * and we fall back to softirqd after that.
  66  *
  67  * This number has been established via experimentation.
  68  * The two things to balance is latency against fairness -
  69  * we want to handle softirqs as soon as possible, but they
  70  * should not be able to lock up the box.
  71  */
  72 #define MAX_SOFTIRQ_RESTART 10
  73
  74 asmlinkage void __do_softirq(void)
  75 {
  76         struct softirq_action *h;
  77         __u32 pending;
  78         int max_restart = MAX_SOFTIRQ_RESTART;
  79         int cpu;
  80
  81         pending = local_softirq_pending();
  82
  83         local_bh_disable();
  84         cpu = smp_processor_id();
  85 restart:
  86         /* Reset the pending bitmask before enabling irqs */
  87         local_softirq_pending() = 0;
  88
  89         local_irq_enable();
  90
  91         h = softirq_vec;
  92
  93         do {
  94                 if (pending & 1) {
  95                         h->action(h);
  96                         rcu_bh_qsctr_inc(cpu);
  97                 }
  98                 h++;
  99                 pending >>= 1;
 100         } while (pending);
 101
 102         local_irq_disable();
 103
 104         pending = local_softirq_pending();
 105         if (pending && --max_restart)
 106                 goto restart;
 107
 108         if (pending)
 109                 wakeup_softirqd();
 110
 111         __local_bh_enable();
 112 }
 113
 114 #ifndef __ARCH_HAS_DO_SOFTIRQ
 115
 116 asmlinkage void do_softirq(void)
 117 {
 118         __u32 pending;
 119         unsigned long flags;
 120
 121         if (in_interrupt())
 122                 return;
 123
 124         local_irq_save(flags);
 125
 126         pending = local_softirq_pending();
 127
 128         if (pending)
 129                 __do_softirq();
 130
 131         local_irq_restore(flags);
 132 }
 133
 134 EXPORT_SYMBOL(do_softirq);
 135
 136 #endif
 137
 138 void local_bh_enable(void)
 139 {
 140         WARN_ON(irqs_disabled());
 141         /*
 142          * Keep preemption disabled until we are done with
 143          * softirq processing:
 144          */
 145         sub_preempt_count(SOFTIRQ_OFFSET - 1);
 146
 147         if (unlikely(!in_interrupt() && local_softirq_pending()))
 148                 do_softirq();
 149
 150         dec_preempt_count();
 151         preempt_check_resched();
 152 }
 153 EXPORT_SYMBOL(local_bh_enable);
 154
 155 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
 156 # define invoke_softirq()       __do_softirq()
 157 #else
 158 # define invoke_softirq()       do_softirq()
 159 #endif
 160
 161 /*
 162  * Exit an interrupt context. Process softirqs if needed and possible:
 163  */
 164 void irq_exit(void)
 165 {
 166         account_system_vtime(current);
 167         sub_preempt_count(IRQ_EXIT_OFFSET);
 168         if (!in_interrupt() && local_softirq_pending())
 169                 invoke_softirq();
 170         preempt_enable_no_resched();
 171 }
 172
 173 /*
 174  * This function must run with irqs disabled!
 175  */
 176 inline fastcall void raise_softirq_irqoff(unsigned int nr)
 177 {
 178         __raise_softirq_irqoff(nr);
 179
 180         /*
 181          * If we're in an interrupt or softirq, we're done
 182          * (this also catches softirq-disabled code). We will
 183          * actually run the softirq once we return from
 184          * the irq or softirq.
 185          *
 186          * Otherwise we wake up ksoftirqd to make sure we
 187          * schedule the softirq soon.
 188          */
 189         if (!in_interrupt())
 190                 wakeup_softirqd();
 191 }
 192
 193 EXPORT_SYMBOL(raise_softirq_irqoff);
 194
 195 void fastcall raise_softirq(unsigned int nr)
 196 {
 197         unsigned long flags;
 198
 199         local_irq_save(flags);
 200         raise_softirq_irqoff(nr);
 201         local_irq_restore(flags);
 202 }
 203
 204 void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
 205 {
 206         softirq_vec[nr].data = data;
 207         softirq_vec[nr].action = action;
 208 }
 209
 210 EXPORT_SYMBOL(open_softirq);
 211
 212 /* Tasklets */
 213 struct tasklet_head
 214 {
 215         struct tasklet_struct *list;
 216 };
 217
 218 /* Some compilers disobey section attribute on statics when not
 219    initialized -- RR */
 220 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
 221 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };
 222
 223 void fastcall __tasklet_schedule(struct tasklet_struct *t)
 224 {
 225         unsigned long flags;
 226
 227         local_irq_save(flags);
 228         t->next = __get_cpu_var(tasklet_vec).list;
 229         __get_cpu_var(tasklet_vec).list = t;
 230         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 231         local_irq_restore(flags);
 232 }
 233
 234 EXPORT_SYMBOL(__tasklet_schedule);
 235
 236 void fastcall __tasklet_hi_schedule(struct tasklet_struct *t)
 237 {
 238         unsigned long flags;
 239
 240         local_irq_save(flags);
 241         t->next = __get_cpu_var(tasklet_hi_vec).list;
 242         __get_cpu_var(tasklet_hi_vec).list = t;
 243         raise_softirq_irqoff(HI_SOFTIRQ);
 244         local_irq_restore(flags);
 245 }
 246
 247 EXPORT_SYMBOL(__tasklet_hi_schedule);
 248
 249 static void tasklet_action(struct softirq_action *a)
 250 {
 251         struct tasklet_struct *list;
 252
 253         local_irq_disable();
 254         list = __get_cpu_var(tasklet_vec).list;
 255         __get_cpu_var(tasklet_vec).list = NULL;
 256         local_irq_enable();
 257
 258         while (list) {
 259                 struct tasklet_struct *t = list;
 260
 261                 list = list->next;
 262
 263                 if (tasklet_trylock(t)) {
 264                         if (!atomic_read(&t->count)) {
 265                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 266                                         BUG();
 267                                 t->func(t->data);
 268                                 tasklet_unlock(t);
 269                                 continue;
 270                         }
 271                         tasklet_unlock(t);
 272                 }
 273
 274                 local_irq_disable();
 275                 t->next = __get_cpu_var(tasklet_vec).list;
 276                 __get_cpu_var(tasklet_vec).list = t;
 277                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 278                 local_irq_enable();
 279         }
 280 }
 281
 282 static void tasklet_hi_action(struct softirq_action *a)
 283 {
 284         struct tasklet_struct *list;
 285
 286         local_irq_disable();
 287         list = __get_cpu_var(tasklet_hi_vec).list;
 288         __get_cpu_var(tasklet_hi_vec).list = NULL;
 289         local_irq_enable();
 290
 291         while (list) {
 292                 struct tasklet_struct *t = list;
 293
 294                 list = list->next;
 295
 296                 if (tasklet_trylock(t)) {
 297                         if (!atomic_read(&t->count)) {
 298                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 299                                         BUG();
 300                                 t->func(t->data);
 301                                 tasklet_unlock(t);
 302                                 continue;
 303                         }
 304                         tasklet_unlock(t);
 305                 }
 306
 307                 local_irq_disable();
 308                 t->next = __get_cpu_var(tasklet_hi_vec).list;
 309                 __get_cpu_var(tasklet_hi_vec).list = t;
 310                 __raise_softirq_irqoff(HI_SOFTIRQ);
 311                 local_irq_enable();
 312         }
 313 }
 314
 315
 316 void tasklet_init(struct tasklet_struct *t,
 317                   void (*func)(unsigned long), unsigned long data)
 318 {
 319         t->next = NULL;
 320         t->state = 0;
 321         atomic_set(&t->count, 0);
 322         t->func = func;
 323         t->data = data;
 324 }
 325
 326 EXPORT_SYMBOL(tasklet_init);
 327
 328 void tasklet_kill(struct tasklet_struct *t)
 329 {
 330         if (in_interrupt())
 331                 printk("Attempt to kill tasklet from interrupt\n");
 332
 333         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 334                 do
 335                         yield();
 336                 while (test_bit(TASKLET_STATE_SCHED, &t->state));
 337         }
 338         tasklet_unlock_wait(t);
 339         clear_bit(TASKLET_STATE_SCHED, &t->state);
 340 }
 341
 342 EXPORT_SYMBOL(tasklet_kill);
 343
 344 void __init softirq_init(void)
 345 {
 346         open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
 347         open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
 348 }
 349
 350 static int ksoftirqd(void * __bind_cpu)
 351 {
 352         set_user_nice(current, 19);
 353         current->flags |= PF_NOFREEZE;
 354
 355         set_current_state(TASK_INTERRUPTIBLE);
 356
 357         while (!kthread_should_stop()) {
 358                 preempt_disable();
 359                 if (!local_softirq_pending()) {
 360                         preempt_enable_no_resched();
 361                         schedule();
 362                         preempt_disable();
 363                 }
 364
 365                 __set_current_state(TASK_RUNNING);
 366
 367                 while (local_softirq_pending()) {
 368                         /* Preempt disable stops cpu going offline.
 369                            If already offline, we'll be on wrong CPU:
 370                            don't process */
 371                         if (cpu_is_offline((long)__bind_cpu))
 372                                 goto wait_to_die;
 373                         do_softirq();
 374                         preempt_enable_no_resched();
 375                         cond_resched();
 376                         preempt_disable();
 377                 }
 378                 preempt_enable();
 379                 set_current_state(TASK_INTERRUPTIBLE);
 380         }
 381         __set_current_state(TASK_RUNNING);
 382         return 0;
 383
 384 wait_to_die:
 385         preempt_enable();
 386         /* Wait for kthread_stop */
 387         set_current_state(TASK_INTERRUPTIBLE);
 388         while (!kthread_should_stop()) {
 389                 schedule();
 390                 set_current_state(TASK_INTERRUPTIBLE);
 391         }
 392         __set_current_state(TASK_RUNNING);
 393         return 0;
 394 }
 395
 396 #ifdef CONFIG_HOTPLUG_CPU
 397 /*
 398  * tasklet_kill_immediate is called to remove a tasklet which can already be
 399  * scheduled for execution on @cpu.
 400  *
 401  * Unlike tasklet_kill, this function removes the tasklet
 402  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 403  *
 404  * When this function is called, @cpu must be in the CPU_DEAD state.
 405  */
 406 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 407 {
 408         struct tasklet_struct **i;
 409
 410         BUG_ON(cpu_online(cpu));
 411         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 412
 413         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 414                 return;
 415
 416         /* CPU is dead, so no lock needed. */
 417         for (i = &per_cpu(tasklet_vec, cpu).list; *i; i = &(*i)->next) {
 418                 if (*i == t) {
 419                         *i = t->next;
 420                         return;
 421                 }
 422         }
 423         BUG();
 424 }
 425
 426 static void takeover_tasklets(unsigned int cpu)
 427 {
 428         struct tasklet_struct **i;
 429
 430         /* CPU is dead, so no lock needed. */
 431         local_irq_disable();
 432
 433         /* Find end, append list for that CPU. */
 434         for (i = &__get_cpu_var(tasklet_vec).list; *i; i = &(*i)->next);
 435         *i = per_cpu(tasklet_vec, cpu).list;
 436         per_cpu(tasklet_vec, cpu).list = NULL;
 437         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 438
 439         for (i = &__get_cpu_var(tasklet_hi_vec).list; *i; i = &(*i)->next);
 440         *i = per_cpu(tasklet_hi_vec, cpu).list;
 441         per_cpu(tasklet_hi_vec, cpu).list = NULL;
 442         raise_softirq_irqoff(HI_SOFTIRQ);
 443
 444         local_irq_enable();
 445 }
 446 #endif /* CONFIG_HOTPLUG_CPU */
 447
 448 static int __devinit cpu_callback(struct notifier_block *nfb,
 449                                   unsigned long action,
 450                                   void *hcpu)
 451 {
 452         int hotcpu = (unsigned long)hcpu;
 453         struct task_struct *p;
 454
 455         switch (action) {
 456         case CPU_UP_PREPARE:
 457                 BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
 458                 BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
 459                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 460                 if (IS_ERR(p)) {
 461                         printk("ksoftirqd for %i failed\n", hotcpu);
 462                         return NOTIFY_BAD;
 463                 }
 464                 kthread_bind(p, hotcpu);
 465                 per_cpu(ksoftirqd, hotcpu) = p;
 466                 break;
 467         case CPU_ONLINE:
 468                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
 469                 break;
 470 #ifdef CONFIG_HOTPLUG_CPU
 471         case CPU_UP_CANCELED:
 472                 /* Unbind so it can run.  Fall thru. */
 473                 kthread_bind(per_cpu(ksoftirqd, hotcpu), smp_processor_id());
 474         case CPU_DEAD:
 475                 p = per_cpu(ksoftirqd, hotcpu);
 476                 per_cpu(ksoftirqd, hotcpu) = NULL;
 477                 kthread_stop(p);
 478                 takeover_tasklets(hotcpu);
 479                 break;
 480 #endif /* CONFIG_HOTPLUG_CPU */
 481         }
 482         return NOTIFY_OK;
 483 }
 484
 485 static struct notifier_block __devinitdata cpu_nfb = {
 486         .notifier_call = cpu_callback
 487 };
 488
 489 __init int spawn_ksoftirqd(void)
 490 {
 491         void *cpu = (void *)(long)smp_processor_id();
 492         cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 493         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 494         register_cpu_notifier(&cpu_nfb);
 495         return 0;
 496 }