git.oblomov.eu Git - linux-2.6/blob - 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 *head;
 360         struct tasklet_struct **tail;
 361 };
 362
 363 /* Some compilers disobey section attribute on statics when not
 364    initialized -- RR */
 365 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
 366 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };
 367
 368 void __tasklet_schedule(struct tasklet_struct *t)
 369 {
 370         unsigned long flags;
 371
 372         local_irq_save(flags);
 373         t->next = NULL;
 374         *__get_cpu_var(tasklet_vec).tail = t;
 375         __get_cpu_var(tasklet_vec).tail = &(t->next);
 376         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 377         local_irq_restore(flags);
 378 }
 379
 380 EXPORT_SYMBOL(__tasklet_schedule);
 381
 382 void __tasklet_hi_schedule(struct tasklet_struct *t)
 383 {
 384         unsigned long flags;
 385
 386         local_irq_save(flags);
 387         t->next = NULL;
 388         *__get_cpu_var(tasklet_hi_vec).tail = t;
 389         __get_cpu_var(tasklet_hi_vec).tail = &(t->next);
 390         raise_softirq_irqoff(HI_SOFTIRQ);
 391         local_irq_restore(flags);
 392 }
 393
 394 EXPORT_SYMBOL(__tasklet_hi_schedule);
 395
 396 static void tasklet_action(struct softirq_action *a)
 397 {
 398         struct tasklet_struct *list;
 399
 400         local_irq_disable();
 401         list = __get_cpu_var(tasklet_vec).head;
 402         __get_cpu_var(tasklet_vec).head = NULL;
 403         __get_cpu_var(tasklet_vec).tail = &__get_cpu_var(tasklet_vec).head;
 404         local_irq_enable();
 405
 406         while (list) {
 407                 struct tasklet_struct *t = list;
 408
 409                 list = list->next;
 410
 411                 if (tasklet_trylock(t)) {
 412                         if (!atomic_read(&t->count)) {
 413                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 414                                         BUG();
 415                                 t->func(t->data);
 416                                 tasklet_unlock(t);
 417                                 continue;
 418                         }
 419                         tasklet_unlock(t);
 420                 }
 421
 422                 local_irq_disable();
 423                 t->next = NULL;
 424                 *__get_cpu_var(tasklet_vec).tail = t;
 425                 __get_cpu_var(tasklet_vec).tail = &(t->next);
 426                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
 427                 local_irq_enable();
 428         }
 429 }
 430
 431 static void tasklet_hi_action(struct softirq_action *a)
 432 {
 433         struct tasklet_struct *list;
 434
 435         local_irq_disable();
 436         list = __get_cpu_var(tasklet_hi_vec).head;
 437         __get_cpu_var(tasklet_hi_vec).head = NULL;
 438         __get_cpu_var(tasklet_hi_vec).tail = &__get_cpu_var(tasklet_hi_vec).head;
 439         local_irq_enable();
 440
 441         while (list) {
 442                 struct tasklet_struct *t = list;
 443
 444                 list = list->next;
 445
 446                 if (tasklet_trylock(t)) {
 447                         if (!atomic_read(&t->count)) {
 448                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
 449                                         BUG();
 450                                 t->func(t->data);
 451                                 tasklet_unlock(t);
 452                                 continue;
 453                         }
 454                         tasklet_unlock(t);
 455                 }
 456
 457                 local_irq_disable();
 458                 t->next = NULL;
 459                 *__get_cpu_var(tasklet_hi_vec).tail = t;
 460                 __get_cpu_var(tasklet_hi_vec).tail = &(t->next);
 461                 __raise_softirq_irqoff(HI_SOFTIRQ);
 462                 local_irq_enable();
 463         }
 464 }
 465
 466
 467 void tasklet_init(struct tasklet_struct *t,
 468                   void (*func)(unsigned long), unsigned long data)
 469 {
 470         t->next = NULL;
 471         t->state = 0;
 472         atomic_set(&t->count, 0);
 473         t->func = func;
 474         t->data = data;
 475 }
 476
 477 EXPORT_SYMBOL(tasklet_init);
 478
 479 void tasklet_kill(struct tasklet_struct *t)
 480 {
 481         if (in_interrupt())
 482                 printk("Attempt to kill tasklet from interrupt\n");
 483
 484         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 485                 do
 486                         yield();
 487                 while (test_bit(TASKLET_STATE_SCHED, &t->state));
 488         }
 489         tasklet_unlock_wait(t);
 490         clear_bit(TASKLET_STATE_SCHED, &t->state);
 491 }
 492
 493 EXPORT_SYMBOL(tasklet_kill);
 494
 495 void __init softirq_init(void)
 496 {
 497         int cpu;
 498
 499         for_each_possible_cpu(cpu) {
 500                 per_cpu(tasklet_vec, cpu).tail =
 501                         &per_cpu(tasklet_vec, cpu).head;
 502                 per_cpu(tasklet_hi_vec, cpu).tail =
 503                         &per_cpu(tasklet_hi_vec, cpu).head;
 504         }
 505
 506         open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
 507         open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
 508 }
 509
 510 static int ksoftirqd(void * __bind_cpu)
 511 {
 512         set_current_state(TASK_INTERRUPTIBLE);
 513
 514         while (!kthread_should_stop()) {
 515                 preempt_disable();
 516                 if (!local_softirq_pending()) {
 517                         preempt_enable_no_resched();
 518                         schedule();
 519                         preempt_disable();
 520                 }
 521
 522                 __set_current_state(TASK_RUNNING);
 523
 524                 while (local_softirq_pending()) {
 525                         /* Preempt disable stops cpu going offline.
 526                            If already offline, we'll be on wrong CPU:
 527                            don't process */
 528                         if (cpu_is_offline((long)__bind_cpu))
 529                                 goto wait_to_die;
 530                         do_softirq();
 531                         preempt_enable_no_resched();
 532                         cond_resched();
 533                         preempt_disable();
 534                 }
 535                 preempt_enable();
 536                 set_current_state(TASK_INTERRUPTIBLE);
 537         }
 538         __set_current_state(TASK_RUNNING);
 539         return 0;
 540
 541 wait_to_die:
 542         preempt_enable();
 543         /* Wait for kthread_stop */
 544         set_current_state(TASK_INTERRUPTIBLE);
 545         while (!kthread_should_stop()) {
 546                 schedule();
 547                 set_current_state(TASK_INTERRUPTIBLE);
 548         }
 549         __set_current_state(TASK_RUNNING);
 550         return 0;
 551 }
 552
 553 #ifdef CONFIG_HOTPLUG_CPU
 554 /*
 555  * tasklet_kill_immediate is called to remove a tasklet which can already be
 556  * scheduled for execution on @cpu.
 557  *
 558  * Unlike tasklet_kill, this function removes the tasklet
 559  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
 560  *
 561  * When this function is called, @cpu must be in the CPU_DEAD state.
 562  */
 563 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
 564 {
 565         struct tasklet_struct **i;
 566
 567         BUG_ON(cpu_online(cpu));
 568         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
 569
 570         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
 571                 return;
 572
 573         /* CPU is dead, so no lock needed. */
 574         for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
 575                 if (*i == t) {
 576                         *i = t->next;
 577                         /* If this was the tail element, move the tail ptr */
 578                         if (*i == NULL)
 579                                 per_cpu(tasklet_vec, cpu).tail = i;
 580                         return;
 581                 }
 582         }
 583         BUG();
 584 }
 585
 586 static void takeover_tasklets(unsigned int cpu)
 587 {
 588         /* CPU is dead, so no lock needed. */
 589         local_irq_disable();
 590
 591         /* Find end, append list for that CPU. */
 592         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 593                 *(__get_cpu_var(tasklet_vec).tail) = per_cpu(tasklet_vec, cpu).head;
 594                 __get_cpu_var(tasklet_vec).tail = per_cpu(tasklet_vec, cpu).tail;
 595                 per_cpu(tasklet_vec, cpu).head = NULL;
 596                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 597         }
 598         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 599
 600         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 601                 *__get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).head;
 602                 __get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).tail;
 603                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 604                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 605         }
 606         raise_softirq_irqoff(HI_SOFTIRQ);
 607
 608         local_irq_enable();
 609 }
 610 #endif /* CONFIG_HOTPLUG_CPU */
 611
 612 static int __cpuinit cpu_callback(struct notifier_block *nfb,
 613                                   unsigned long action,
 614                                   void *hcpu)
 615 {
 616         int hotcpu = (unsigned long)hcpu;
 617         struct task_struct *p;
 618
 619         switch (action) {
 620         case CPU_UP_PREPARE:
 621         case CPU_UP_PREPARE_FROZEN:
 622                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 623                 if (IS_ERR(p)) {
 624                         printk("ksoftirqd for %i failed\n", hotcpu);
 625                         return NOTIFY_BAD;
 626                 }
 627                 kthread_bind(p, hotcpu);
 628                 per_cpu(ksoftirqd, hotcpu) = p;
 629                 break;
 630         case CPU_ONLINE:
 631         case CPU_ONLINE_FROZEN:
 632                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
 633                 break;
 634 #ifdef CONFIG_HOTPLUG_CPU
 635         case CPU_UP_CANCELED:
 636         case CPU_UP_CANCELED_FROZEN:
 637                 if (!per_cpu(ksoftirqd, hotcpu))
 638                         break;
 639                 /* Unbind so it can run.  Fall thru. */
 640                 kthread_bind(per_cpu(ksoftirqd, hotcpu),
 641                              any_online_cpu(cpu_online_map));
 642         case CPU_DEAD:
 643         case CPU_DEAD_FROZEN: {
 644                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 645
 646                 p = per_cpu(ksoftirqd, hotcpu);
 647                 per_cpu(ksoftirqd, hotcpu) = NULL;
 648                 sched_setscheduler(p, SCHED_FIFO, &param);
 649                 kthread_stop(p);
 650                 takeover_tasklets(hotcpu);
 651                 break;
 652         }
 653 #endif /* CONFIG_HOTPLUG_CPU */
 654         }
 655         return NOTIFY_OK;
 656 }
 657
 658 static struct notifier_block __cpuinitdata cpu_nfb = {
 659         .notifier_call = cpu_callback
 660 };
 661
 662 __init int spawn_ksoftirqd(void)
 663 {
 664         void *cpu = (void *)(long)smp_processor_id();
 665         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 666
 667         BUG_ON(err == NOTIFY_BAD);
 668         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 669         register_cpu_notifier(&cpu_nfb);
 670         return 0;
 671 }
 672
 673 #ifdef CONFIG_SMP
 674 /*
 675  * Call a function on all processors
 676  */
 677 int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait)
 678 {
 679         int ret = 0;
 680
 681         preempt_disable();
 682         ret = smp_call_function(func, info, retry, wait);
 683         local_irq_disable();
 684         func(info);
 685         local_irq_enable();
 686         preempt_enable();
 687         return ret;
 688 }
 689 EXPORT_SYMBOL(on_each_cpu);
 690 #endif