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