kernel/smp.c

   1 /*
   2  * Generic helpers for smp ipi calls
   3  *
   4  * (C) Jens Axboe <jens.axboe@oracle.com> 2008
   5  */
   6 #include <linux/rcupdate.h>
   7 #include <linux/rculist.h>
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/percpu.h>
  11 #include <linux/init.h>
  12 #include <linux/smp.h>
  13 #include <linux/cpu.h>
  14
  15 static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
  16
  17 static struct {
  18         struct list_head        queue;
  19         spinlock_t              lock;
  20 } call_function __cacheline_aligned_in_smp =
  21         {
  22                 .queue          = LIST_HEAD_INIT(call_function.queue),
  23                 .lock           = __SPIN_LOCK_UNLOCKED(call_function.lock),
  24         };
  25
  26 enum {
  27         CSD_FLAG_LOCK           = 0x01,
  28 };
  29
  30 struct call_function_data {
  31         struct call_single_data csd;
  32         atomic_t                refs;
  33         cpumask_var_t           cpumask;
  34 };
  35
  36 struct call_single_queue {
  37         struct list_head        list;
  38         spinlock_t              lock;
  39 };
  40
  41 static DEFINE_PER_CPU(struct call_function_data, cfd_data);
  42
  43 static int
  44 hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
  45 {
  46         long cpu = (long)hcpu;
  47         struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
  48
  49         switch (action) {
  50         case CPU_UP_PREPARE:
  51         case CPU_UP_PREPARE_FROZEN:
  52                 if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
  53                                 cpu_to_node(cpu)))
  54                         return NOTIFY_BAD;
  55                 break;
  56
  57 #ifdef CONFIG_HOTPLUG_CPU
  58         case CPU_UP_CANCELED:
  59         case CPU_UP_CANCELED_FROZEN:
  60
  61         case CPU_DEAD:
  62         case CPU_DEAD_FROZEN:
  63                 free_cpumask_var(cfd->cpumask);
  64                 break;
  65 #endif
  66         };
  67
  68         return NOTIFY_OK;
  69 }
  70
  71 static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
  72         .notifier_call          = hotplug_cfd,
  73 };
  74
  75 static int __cpuinit init_call_single_data(void)
  76 {
  77         void *cpu = (void *)(long)smp_processor_id();
  78         int i;
  79
  80         for_each_possible_cpu(i) {
  81                 struct call_single_queue *q = &per_cpu(call_single_queue, i);
  82
  83                 spin_lock_init(&q->lock);
  84                 INIT_LIST_HEAD(&q->list);
  85         }
  86
  87         hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
  88         register_cpu_notifier(&hotplug_cfd_notifier);
  89
  90         return 0;
  91 }
  92 early_initcall(init_call_single_data);
  93
  94 /*
  95  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
  96  *
  97  * For non-synchronous ipi calls the csd can still be in use by the
  98  * previous function call. For multi-cpu calls its even more interesting
  99  * as we'll have to ensure no other cpu is observing our csd.
 100  */
 101 static void csd_lock_wait(struct call_single_data *data)
 102 {
 103         while (data->flags & CSD_FLAG_LOCK)
 104                 cpu_relax();
 105 }
 106
 107 static void csd_lock(struct call_single_data *data)
 108 {
 109         csd_lock_wait(data);
 110         data->flags = CSD_FLAG_LOCK;
 111
 112         /*
 113          * prevent CPU from reordering the above assignment
 114          * to ->flags with any subsequent assignments to other
 115          * fields of the specified call_single_data structure:
 116          */
 117         smp_mb();
 118 }
 119
 120 static void csd_unlock(struct call_single_data *data)
 121 {
 122         WARN_ON(!(data->flags & CSD_FLAG_LOCK));
 123
 124         /*
 125          * ensure we're all done before releasing data:
 126          */
 127         smp_mb();
 128
 129         data->flags &= ~CSD_FLAG_LOCK;
 130 }
 131
 132 /*
 133  * Insert a previously allocated call_single_data element
 134  * for execution on the given CPU. data must already have
 135  * ->func, ->info, and ->flags set.
 136  */
 137 static
 138 void generic_exec_single(int cpu, struct call_single_data *data, int wait)
 139 {
 140         struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
 141         unsigned long flags;
 142         int ipi;
 143
 144         spin_lock_irqsave(&dst->lock, flags);
 145         ipi = list_empty(&dst->list);
 146         list_add_tail(&data->list, &dst->list);
 147         spin_unlock_irqrestore(&dst->lock, flags);
 148
 149         /*
 150          * The list addition should be visible before sending the IPI
 151          * handler locks the list to pull the entry off it because of
 152          * normal cache coherency rules implied by spinlocks.
 153          *
 154          * If IPIs can go out of order to the cache coherency protocol
 155          * in an architecture, sufficient synchronisation should be added
 156          * to arch code to make it appear to obey cache coherency WRT
 157          * locking and barrier primitives. Generic code isn't really
 158          * equipped to do the right thing...
 159          */
 160         if (ipi)
 161                 arch_send_call_function_single_ipi(cpu);
 162
 163         if (wait)
 164                 csd_lock_wait(data);
 165 }
 166
 167 /*
 168  * Invoked by arch to handle an IPI for call function. Must be called with
 169  * interrupts disabled.
 170  */
 171 void generic_smp_call_function_interrupt(void)
 172 {
 173         struct call_function_data *data;
 174         int cpu = get_cpu();
 175
 176         /*
 177          * Shouldn't receive this interrupt on a cpu that is not yet online.
 178          */
 179         WARN_ON_ONCE(!cpu_online(cpu));
 180
 181         /*
 182          * Ensure entry is visible on call_function_queue after we have
 183          * entered the IPI. See comment in smp_call_function_many.
 184          * If we don't have this, then we may miss an entry on the list
 185          * and never get another IPI to process it.
 186          */
 187         smp_mb();
 188
 189         /*
 190          * It's ok to use list_for_each_rcu() here even though we may
 191          * delete 'pos', since list_del_rcu() doesn't clear ->next
 192          */
 193         list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
 194                 int refs;
 195
 196                 if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
 197                         continue;
 198
 199                 data->csd.func(data->csd.info);
 200
 201                 refs = atomic_dec_return(&data->refs);
 202                 WARN_ON(refs < 0);
 203                 if (!refs) {
 204                         spin_lock(&call_function.lock);
 205                         list_del_rcu(&data->csd.list);
 206                         spin_unlock(&call_function.lock);
 207                 }
 208
 209                 if (refs)
 210                         continue;
 211
 212                 csd_unlock(&data->csd);
 213         }
 214
 215         put_cpu();
 216 }
 217
 218 /*
 219  * Invoked by arch to handle an IPI for call function single. Must be
 220  * called from the arch with interrupts disabled.
 221  */
 222 void generic_smp_call_function_single_interrupt(void)
 223 {
 224         struct call_single_queue *q = &__get_cpu_var(call_single_queue);
 225         unsigned int data_flags;
 226         LIST_HEAD(list);
 227
 228         /*
 229          * Shouldn't receive this interrupt on a cpu that is not yet online.
 230          */
 231         WARN_ON_ONCE(!cpu_online(smp_processor_id()));
 232
 233         spin_lock(&q->lock);
 234         list_replace_init(&q->list, &list);
 235         spin_unlock(&q->lock);
 236
 237         while (!list_empty(&list)) {
 238                 struct call_single_data *data;
 239
 240                 data = list_entry(list.next, struct call_single_data, list);
 241                 list_del(&data->list);
 242
 243                 /*
 244                  * 'data' can be invalid after this call if flags == 0
 245                  * (when called through generic_exec_single()),
 246                  * so save them away before making the call:
 247                  */
 248                 data_flags = data->flags;
 249
 250                 data->func(data->info);
 251
 252                 /*
 253                  * Unlocked CSDs are valid through generic_exec_single():
 254                  */
 255                 if (data_flags & CSD_FLAG_LOCK)
 256                         csd_unlock(data);
 257         }
 258 }
 259
 260 static DEFINE_PER_CPU(struct call_single_data, csd_data);
 261
 262 /*
 263  * smp_call_function_single - Run a function on a specific CPU
 264  * @func: The function to run. This must be fast and non-blocking.
 265  * @info: An arbitrary pointer to pass to the function.
 266  * @wait: If true, wait until function has completed on other CPUs.
 267  *
 268  * Returns 0 on success, else a negative status code. Note that @wait
 269  * will be implicitly turned on in case of allocation failures, since
 270  * we fall back to on-stack allocation.
 271  */
 272 int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 273                              int wait)
 274 {
 275         struct call_single_data d = {
 276                 .flags = 0,
 277         };
 278         unsigned long flags;
 279         int this_cpu;
 280         int err = 0;
 281
 282         /*
 283          * prevent preemption and reschedule on another processor,
 284          * as well as CPU removal
 285          */
 286         this_cpu = get_cpu();
 287
 288         /*
 289          * Can deadlock when called with interrupts disabled.
 290          * We allow cpu's that are not yet online though, as no one else can
 291          * send smp call function interrupt to this cpu and as such deadlocks
 292          * can't happen.
 293          */
 294         WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 295                      && !oops_in_progress);
 296
 297         if (cpu == this_cpu) {
 298                 local_irq_save(flags);
 299                 func(info);
 300                 local_irq_restore(flags);
 301         } else {
 302                 if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
 303                         struct call_single_data *data = &d;
 304
 305                         if (!wait)
 306                                 data = &__get_cpu_var(csd_data);
 307
 308                         csd_lock(data);
 309
 310                         data->func = func;
 311                         data->info = info;
 312                         generic_exec_single(cpu, data, wait);
 313                 } else {
 314                         err = -ENXIO;   /* CPU not online */
 315                 }
 316         }
 317
 318         put_cpu();
 319
 320         return err;
 321 }
 322 EXPORT_SYMBOL(smp_call_function_single);
 323
 324 /**
 325  * __smp_call_function_single(): Run a function on another CPU
 326  * @cpu: The CPU to run on.
 327  * @data: Pre-allocated and setup data structure
 328  *
 329  * Like smp_call_function_single(), but allow caller to pass in a
 330  * pre-allocated data structure. Useful for embedding @data inside
 331  * other structures, for instance.
 332  */
 333 void __smp_call_function_single(int cpu, struct call_single_data *data,
 334                                 int wait)
 335 {
 336         csd_lock(data);
 337
 338         /*
 339          * Can deadlock when called with interrupts disabled.
 340          * We allow cpu's that are not yet online though, as no one else can
 341          * send smp call function interrupt to this cpu and as such deadlocks
 342          * can't happen.
 343          */
 344         WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
 345                      && !oops_in_progress);
 346
 347         generic_exec_single(cpu, data, wait);
 348 }
 349
 350 /**
 351  * smp_call_function_many(): Run a function on a set of other CPUs.
 352  * @mask: The set of cpus to run on (only runs on online subset).
 353  * @func: The function to run. This must be fast and non-blocking.
 354  * @info: An arbitrary pointer to pass to the function.
 355  * @wait: If true, wait (atomically) until function has completed
 356  *        on other CPUs.
 357  *
 358  * If @wait is true, then returns once @func has returned. Note that @wait
 359  * will be implicitly turned on in case of allocation failures, since
 360  * we fall back to on-stack allocation.
 361  *
 362  * You must not call this function with disabled interrupts or from a
 363  * hardware interrupt handler or from a bottom half handler. Preemption
 364  * must be disabled when calling this function.
 365  */
 366 void smp_call_function_many(const struct cpumask *mask,
 367                             void (*func)(void *), void *info, bool wait)
 368 {
 369         struct call_function_data *data;
 370         unsigned long flags;
 371         int cpu, next_cpu, this_cpu = smp_processor_id();
 372
 373         /*
 374          * Can deadlock when called with interrupts disabled.
 375          * We allow cpu's that are not yet online though, as no one else can
 376          * send smp call function interrupt to this cpu and as such deadlocks
 377          * can't happen.
 378          */
 379         WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 380                      && !oops_in_progress);
 381
 382         /* So, what's a CPU they want? Ignoring this one. */
 383         cpu = cpumask_first_and(mask, cpu_online_mask);
 384         if (cpu == this_cpu)
 385                 cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 386
 387         /* No online cpus?  We're done. */
 388         if (cpu >= nr_cpu_ids)
 389                 return;
 390
 391         /* Do we have another CPU which isn't us? */
 392         next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 393         if (next_cpu == this_cpu)
 394                 next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
 395
 396         /* Fastpath: do that cpu by itself. */
 397         if (next_cpu >= nr_cpu_ids) {
 398                 smp_call_function_single(cpu, func, info, wait);
 399                 return;
 400         }
 401
 402         data = &__get_cpu_var(cfd_data);
 403         csd_lock(&data->csd);
 404
 405         data->csd.func = func;
 406         data->csd.info = info;
 407         cpumask_and(data->cpumask, mask, cpu_online_mask);
 408         cpumask_clear_cpu(this_cpu, data->cpumask);
 409         atomic_set(&data->refs, cpumask_weight(data->cpumask));
 410
 411         spin_lock_irqsave(&call_function.lock, flags);
 412         /*
 413          * Place entry at the _HEAD_ of the list, so that any cpu still
 414          * observing the entry in generic_smp_call_function_interrupt()
 415          * will not miss any other list entries:
 416          */
 417         list_add_rcu(&data->csd.list, &call_function.queue);
 418         spin_unlock_irqrestore(&call_function.lock, flags);
 419
 420         /*
 421          * Make the list addition visible before sending the ipi.
 422          * (IPIs must obey or appear to obey normal Linux cache
 423          * coherency rules -- see comment in generic_exec_single).
 424          */
 425         smp_mb();
 426
 427         /* Send a message to all CPUs in the map */
 428         arch_send_call_function_ipi_mask(data->cpumask);
 429
 430         /* Optionally wait for the CPUs to complete */
 431         if (wait)
 432                 csd_lock_wait(&data->csd);
 433 }
 434 EXPORT_SYMBOL(smp_call_function_many);
 435
 436 /**
 437  * smp_call_function(): Run a function on all other CPUs.
 438  * @func: The function to run. This must be fast and non-blocking.
 439  * @info: An arbitrary pointer to pass to the function.
 440  * @wait: If true, wait (atomically) until function has completed
 441  *        on other CPUs.
 442  *
 443  * Returns 0.
 444  *
 445  * If @wait is true, then returns once @func has returned; otherwise
 446  * it returns just before the target cpu calls @func. In case of allocation
 447  * failure, @wait will be implicitly turned on.
 448  *
 449  * You must not call this function with disabled interrupts or from a
 450  * hardware interrupt handler or from a bottom half handler.
 451  */
 452 int smp_call_function(void (*func)(void *), void *info, int wait)
 453 {
 454         preempt_disable();
 455         smp_call_function_many(cpu_online_mask, func, info, wait);
 456         preempt_enable();
 457
 458         return 0;
 459 }
 460 EXPORT_SYMBOL(smp_call_function);
 461
 462 void ipi_call_lock(void)
 463 {
 464         spin_lock(&call_function.lock);
 465 }
 466
 467 void ipi_call_unlock(void)
 468 {
 469         spin_unlock(&call_function.lock);
 470 }
 471
 472 void ipi_call_lock_irq(void)
 473 {
 474         spin_lock_irq(&call_function.lock);
 475 }
 476
 477 void ipi_call_unlock_irq(void)
 478 {
 479         spin_unlock_irq(&call_function.lock);
 480 }