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                 if (!local_softirq_pending())
 359                         schedule();
 360
 361                 __set_current_state(TASK_RUNNING);
 362
 363                 while (local_softirq_pending()) {
 364                         /* Preempt disable stops cpu going offline.
 365                            If already offline, we'll be on wrong CPU:
 366                            don't process */
 367                         preempt_disable();
 368                         if (cpu_is_offline((long)__bind_cpu))
 369                                 goto wait_to_die;
 370                         do_softirq();
 371                         preempt_enable();
 372                         cond_resched();
 373                 }
 374
 375                 set_current_state(TASK_INTERRUPTIBLE);
 376         }
 377         __set_current_state(TASK_RUNNING);
 378         return 0;
 379
 380 wait_to_die:
 381         preempt_enable();
 382         /* Wait for kthread_stop */
 383         set_current_state(TASK_INTERRUPTIBLE);
 384         while (!kthread_should_stop()) {
 385                 schedule();
 386                 set_current_state(TASK_INTERRUPTIBLE);
 387         }
 388         __set_current_state(TASK_RUNNING);
 389         return 0;
 390 }
 391
 392 #ifdef CONFIG_HOTPLUG_CPU
 393 /*
 394  * tasklet_kill_immediate is called to remove a tasklet which can already be
 395  * scheduled for execution on @cpu.
 396  *
 397  * Unlike tasklet_kill, this function removes the tasklet
 398  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 399  *
 400  * When this function is called, @cpu must be in the CPU_DEAD state.
 401  */
 402 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 403 {
 404         struct tasklet_struct **i;
 405
 406         BUG_ON(cpu_online(cpu));
 407         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 408
 409         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 410                 return;
 411
 412         /* CPU is dead, so no lock needed. */
 413         for (i = &per_cpu(tasklet_vec, cpu).list; *i; i = &(*i)->next) {
 414                 if (*i == t) {
 415                         *i = t->next;
 416                         return;
 417                 }
 418         }
 419         BUG();
 420 }
 421
 422 static void takeover_tasklets(unsigned int cpu)
 423 {
 424         struct tasklet_struct **i;
 425
 426         /* CPU is dead, so no lock needed. */
 427         local_irq_disable();
 428
 429         /* Find end, append list for that CPU. */
 430         for (i = &__get_cpu_var(tasklet_vec).list; *i; i = &(*i)->next);
 431         *i = per_cpu(tasklet_vec, cpu).list;
 432         per_cpu(tasklet_vec, cpu).list = NULL;
 433         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 434
 435         for (i = &__get_cpu_var(tasklet_hi_vec).list; *i; i = &(*i)->next);
 436         *i = per_cpu(tasklet_hi_vec, cpu).list;
 437         per_cpu(tasklet_hi_vec, cpu).list = NULL;
 438         raise_softirq_irqoff(HI_SOFTIRQ);
 439
 440         local_irq_enable();
 441 }
 442 #endif /* CONFIG_HOTPLUG_CPU */
 443
 444 static int __devinit cpu_callback(struct notifier_block *nfb,
 445                                   unsigned long action,
 446                                   void *hcpu)
 447 {
 448         int hotcpu = (unsigned long)hcpu;
 449         struct task_struct *p;
 450
 451         switch (action) {
 452         case CPU_UP_PREPARE:
 453                 BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
 454                 BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
 455                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 456                 if (IS_ERR(p)) {
 457                         printk("ksoftirqd for %i failed\n", hotcpu);
 458                         return NOTIFY_BAD;
 459                 }
 460                 kthread_bind(p, hotcpu);
 461                 per_cpu(ksoftirqd, hotcpu) = p;
 462                 break;
 463         case CPU_ONLINE:
 464                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
 465                 break;
 466 #ifdef CONFIG_HOTPLUG_CPU
 467         case CPU_UP_CANCELED:
 468                 /* Unbind so it can run.  Fall thru. */
 469                 kthread_bind(per_cpu(ksoftirqd, hotcpu), smp_processor_id());
 470         case CPU_DEAD:
 471                 p = per_cpu(ksoftirqd, hotcpu);
 472                 per_cpu(ksoftirqd, hotcpu) = NULL;
 473                 kthread_stop(p);
 474                 takeover_tasklets(hotcpu);
 475                 break;
 476 #endif /* CONFIG_HOTPLUG_CPU */
 477         }
 478         return NOTIFY_OK;
 479 }
 480
 481 static struct notifier_block __devinitdata cpu_nfb = {
 482         .notifier_call = cpu_callback
 483 };
 484
 485 __init int spawn_ksoftirqd(void)
 486 {
 487         void *cpu = (void *)(long)smp_processor_id();
 488         cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 489         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 490         register_cpu_notifier(&cpu_nfb);
 491         return 0;
 492 }