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/gfp.h>
  13 #include <linux/smp.h>
  14 #include <linux/cpu.h>
  15
  16 static struct {
  17         struct list_head        queue;
  18         raw_spinlock_t          lock;
  19 } call_function __cacheline_aligned_in_smp =
  20         {
  21                 .queue          = LIST_HEAD_INIT(call_function.queue),
  22                 .lock           = __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),
  23         };
  24
  25 enum {
  26         CSD_FLAG_LOCK           = 0x01,
  27 };
  28
  29 struct call_function_data {
  30         struct call_single_data csd;
  31         atomic_t                refs;
  32         cpumask_var_t           cpumask;
  33 };
  34
  35 static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
  36
  37 struct call_single_queue {
  38         struct list_head        list;
  39         raw_spinlock_t          lock;
  40 };
  41
  42 static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);
  43
  44 static int
  45 hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
  46 {
  47         long cpu = (long)hcpu;
  48         struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
  49
  50         switch (action) {
  51         case CPU_UP_PREPARE:
  52         case CPU_UP_PREPARE_FROZEN:
  53                 if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
  54                                 cpu_to_node(cpu)))
  55                         return notifier_from_errno(-ENOMEM);
  56                 break;
  57
  58 #ifdef CONFIG_HOTPLUG_CPU
  59         case CPU_UP_CANCELED:
  60         case CPU_UP_CANCELED_FROZEN:
  61
  62         case CPU_DEAD:
  63         case CPU_DEAD_FROZEN:
  64                 free_cpumask_var(cfd->cpumask);
  65                 break;
  66 #endif
  67         };
  68
  69         return NOTIFY_OK;
  70 }
  71
  72 static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
  73         .notifier_call          = hotplug_cfd,
  74 };
  75
  76 static int __cpuinit init_call_single_data(void)
  77 {
  78         void *cpu = (void *)(long)smp_processor_id();
  79         int i;
  80
  81         for_each_possible_cpu(i) {
  82                 struct call_single_queue *q = &per_cpu(call_single_queue, i);
  83
  84                 raw_spin_lock_init(&q->lock);
  85                 INIT_LIST_HEAD(&q->list);
  86         }
  87
  88         hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
  89         register_cpu_notifier(&hotplug_cfd_notifier);
  90
  91         return 0;
  92 }
  93 early_initcall(init_call_single_data);
  94
  95 /*
  96  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
  97  *
  98  * For non-synchronous ipi calls the csd can still be in use by the
  99  * previous function call. For multi-cpu calls its even more interesting
 100  * as we'll have to ensure no other cpu is observing our csd.
 101  */
 102 static void csd_lock_wait(struct call_single_data *data)
 103 {
 104         while (data->flags & CSD_FLAG_LOCK)
 105                 cpu_relax();
 106 }
 107
 108 static void csd_lock(struct call_single_data *data)
 109 {
 110         csd_lock_wait(data);
 111         data->flags = CSD_FLAG_LOCK;
 112
 113         /*
 114          * prevent CPU from reordering the above assignment
 115          * to ->flags with any subsequent assignments to other
 116          * fields of the specified call_single_data structure:
 117          */
 118         smp_mb();
 119 }
 120
 121 static void csd_unlock(struct call_single_data *data)
 122 {
 123         WARN_ON(!(data->flags & CSD_FLAG_LOCK));
 124
 125         /*
 126          * ensure we're all done before releasing data:
 127          */
 128         smp_mb();
 129
 130         data->flags &= ~CSD_FLAG_LOCK;
 131 }
 132
 133 /*
 134  * Insert a previously allocated call_single_data element
 135  * for execution on the given CPU. data must already have
 136  * ->func, ->info, and ->flags set.
 137  */
 138 static
 139 void generic_exec_single(int cpu, struct call_single_data *data, int wait)
 140 {
 141         struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
 142         unsigned long flags;
 143         int ipi;
 144
 145         raw_spin_lock_irqsave(&dst->lock, flags);
 146         ipi = list_empty(&dst->list);
 147         list_add_tail(&data->list, &dst->list);
 148         raw_spin_unlock_irqrestore(&dst->lock, flags);
 149
 150         /*
 151          * The list addition should be visible before sending the IPI
 152          * handler locks the list to pull the entry off it because of
 153          * normal cache coherency rules implied by spinlocks.
 154          *
 155          * If IPIs can go out of order to the cache coherency protocol
 156          * in an architecture, sufficient synchronisation should be added
 157          * to arch code to make it appear to obey cache coherency WRT
 158          * locking and barrier primitives. Generic code isn't really
 159          * equipped to do the right thing...
 160          */
 161         if (ipi)
 162                 arch_send_call_function_single_ipi(cpu);
 163
 164         if (wait)
 165                 csd_lock_wait(data);
 166 }
 167
 168 /*
 169  * Invoked by arch to handle an IPI for call function. Must be called with
 170  * interrupts disabled.
 171  */
 172 void generic_smp_call_function_interrupt(void)
 173 {
 174         struct call_function_data *data;
 175         int cpu = smp_processor_id();
 176
 177         /*
 178          * Shouldn't receive this interrupt on a cpu that is not yet online.
 179          */
 180         WARN_ON_ONCE(!cpu_online(cpu));
 181
 182         /*
 183          * Ensure entry is visible on call_function_queue after we have
 184          * entered the IPI. See comment in smp_call_function_many.
 185          * If we don't have this, then we may miss an entry on the list
 186          * and never get another IPI to process it.
 187          */
 188         smp_mb();
 189
 190         /*
 191          * It's ok to use list_for_each_rcu() here even though we may
 192          * delete 'pos', since list_del_rcu() doesn't clear ->next
 193          */
 194         list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
 195                 int refs;
 196
 197                 if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
 198                         continue;
 199
 200                 data->csd.func(data->csd.info);
 201
 202                 refs = atomic_dec_return(&data->refs);
 203                 WARN_ON(refs < 0);
 204                 if (!refs) {
 205                         raw_spin_lock(&call_function.lock);
 206                         list_del_rcu(&data->csd.list);
 207                         raw_spin_unlock(&call_function.lock);
 208                 }
 209
 210                 if (refs)
 211                         continue;
 212
 213                 csd_unlock(&data->csd);
 214         }
 215
 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         raw_spin_lock(&q->lock);
 234         list_replace_init(&q->list, &list);
 235         raw_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_SHARED_ALIGNED(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.
 269  */
 270 int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 271                              int wait)
 272 {
 273         struct call_single_data d = {
 274                 .flags = 0,
 275         };
 276         unsigned long flags;
 277         int this_cpu;
 278         int err = 0;
 279
 280         /*
 281          * prevent preemption and reschedule on another processor,
 282          * as well as CPU removal
 283          */
 284         this_cpu = get_cpu();
 285
 286         /*
 287          * Can deadlock when called with interrupts disabled.
 288          * We allow cpu's that are not yet online though, as no one else can
 289          * send smp call function interrupt to this cpu and as such deadlocks
 290          * can't happen.
 291          */
 292         WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 293                      && !oops_in_progress);
 294
 295         if (cpu == this_cpu) {
 296                 local_irq_save(flags);
 297                 func(info);
 298                 local_irq_restore(flags);
 299         } else {
 300                 if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
 301                         struct call_single_data *data = &d;
 302
 303                         if (!wait)
 304                                 data = &__get_cpu_var(csd_data);
 305
 306                         csd_lock(data);
 307
 308                         data->func = func;
 309                         data->info = info;
 310                         generic_exec_single(cpu, data, wait);
 311                 } else {
 312                         err = -ENXIO;   /* CPU not online */
 313                 }
 314         }
 315
 316         put_cpu();
 317
 318         return err;
 319 }
 320 EXPORT_SYMBOL(smp_call_function_single);
 321
 322 /*
 323  * smp_call_function_any - Run a function on any of the given cpus
 324  * @mask: The mask of cpus it can run on.
 325  * @func: The function to run. This must be fast and non-blocking.
 326  * @info: An arbitrary pointer to pass to the function.
 327  * @wait: If true, wait until function has completed.
 328  *
 329  * Returns 0 on success, else a negative status code (if no cpus were online).
 330  * Note that @wait will be implicitly turned on in case of allocation failures,
 331  * since we fall back to on-stack allocation.
 332  *
 333  * Selection preference:
 334  *      1) current cpu if in @mask
 335  *      2) any cpu of current node if in @mask
 336  *      3) any other online cpu in @mask
 337  */
 338 int smp_call_function_any(const struct cpumask *mask,
 339                           void (*func)(void *info), void *info, int wait)
 340 {
 341         unsigned int cpu;
 342         const struct cpumask *nodemask;
 343         int ret;
 344
 345         /* Try for same CPU (cheapest) */
 346         cpu = get_cpu();
 347         if (cpumask_test_cpu(cpu, mask))
 348                 goto call;
 349
 350         /* Try for same node. */
 351         nodemask = cpumask_of_node(cpu_to_node(cpu));
 352         for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
 353              cpu = cpumask_next_and(cpu, nodemask, mask)) {
 354                 if (cpu_online(cpu))
 355                         goto call;
 356         }
 357
 358         /* Any online will do: smp_call_function_single handles nr_cpu_ids. */
 359         cpu = cpumask_any_and(mask, cpu_online_mask);
 360 call:
 361         ret = smp_call_function_single(cpu, func, info, wait);
 362         put_cpu();
 363         return ret;
 364 }
 365 EXPORT_SYMBOL_GPL(smp_call_function_any);
 366
 367 /**
 368  * __smp_call_function_single(): Run a function on another CPU
 369  * @cpu: The CPU to run on.
 370  * @data: Pre-allocated and setup data structure
 371  *
 372  * Like smp_call_function_single(), but allow caller to pass in a
 373  * pre-allocated data structure. Useful for embedding @data inside
 374  * other structures, for instance.
 375  */
 376 void __smp_call_function_single(int cpu, struct call_single_data *data,
 377                                 int wait)
 378 {
 379         csd_lock(data);
 380
 381         /*
 382          * Can deadlock when called with interrupts disabled.
 383          * We allow cpu's that are not yet online though, as no one else can
 384          * send smp call function interrupt to this cpu and as such deadlocks
 385          * can't happen.
 386          */
 387         WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
 388                      && !oops_in_progress);
 389
 390         generic_exec_single(cpu, data, wait);
 391 }
 392
 393 /**
 394  * smp_call_function_many(): Run a function on a set of other CPUs.
 395  * @mask: The set of cpus to run on (only runs on online subset).
 396  * @func: The function to run. This must be fast and non-blocking.
 397  * @info: An arbitrary pointer to pass to the function.
 398  * @wait: If true, wait (atomically) until function has completed
 399  *        on other CPUs.
 400  *
 401  * If @wait is true, then returns once @func has returned.
 402  *
 403  * You must not call this function with disabled interrupts or from a
 404  * hardware interrupt handler or from a bottom half handler. Preemption
 405  * must be disabled when calling this function.
 406  */
 407 void smp_call_function_many(const struct cpumask *mask,
 408                             void (*func)(void *), void *info, bool wait)
 409 {
 410         struct call_function_data *data;
 411         unsigned long flags;
 412         int cpu, next_cpu, this_cpu = smp_processor_id();
 413
 414         /*
 415          * Can deadlock when called with interrupts disabled.
 416          * We allow cpu's that are not yet online though, as no one else can
 417          * send smp call function interrupt to this cpu and as such deadlocks
 418          * can't happen.
 419          */
 420         WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 421                      && !oops_in_progress);
 422
 423         /* So, what's a CPU they want? Ignoring this one. */
 424         cpu = cpumask_first_and(mask, cpu_online_mask);
 425         if (cpu == this_cpu)
 426                 cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 427
 428         /* No online cpus?  We're done. */
 429         if (cpu >= nr_cpu_ids)
 430                 return;
 431
 432         /* Do we have another CPU which isn't us? */
 433         next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 434         if (next_cpu == this_cpu)
 435                 next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
 436
 437         /* Fastpath: do that cpu by itself. */
 438         if (next_cpu >= nr_cpu_ids) {
 439                 smp_call_function_single(cpu, func, info, wait);
 440                 return;
 441         }
 442
 443         data = &__get_cpu_var(cfd_data);
 444         csd_lock(&data->csd);
 445
 446         data->csd.func = func;
 447         data->csd.info = info;
 448         cpumask_and(data->cpumask, mask, cpu_online_mask);
 449         cpumask_clear_cpu(this_cpu, data->cpumask);
 450         atomic_set(&data->refs, cpumask_weight(data->cpumask));
 451
 452         raw_spin_lock_irqsave(&call_function.lock, flags);
 453         /*
 454          * Place entry at the _HEAD_ of the list, so that any cpu still
 455          * observing the entry in generic_smp_call_function_interrupt()
 456          * will not miss any other list entries:
 457          */
 458         list_add_rcu(&data->csd.list, &call_function.queue);
 459         raw_spin_unlock_irqrestore(&call_function.lock, flags);
 460
 461         /*
 462          * Make the list addition visible before sending the ipi.
 463          * (IPIs must obey or appear to obey normal Linux cache
 464          * coherency rules -- see comment in generic_exec_single).
 465          */
 466         smp_mb();
 467
 468         /* Send a message to all CPUs in the map */
 469         arch_send_call_function_ipi_mask(data->cpumask);
 470
 471         /* Optionally wait for the CPUs to complete */
 472         if (wait)
 473                 csd_lock_wait(&data->csd);
 474 }
 475 EXPORT_SYMBOL(smp_call_function_many);
 476
 477 /**
 478  * smp_call_function(): Run a function on all other CPUs.
 479  * @func: The function to run. This must be fast and non-blocking.
 480  * @info: An arbitrary pointer to pass to the function.
 481  * @wait: If true, wait (atomically) until function has completed
 482  *        on other CPUs.
 483  *
 484  * Returns 0.
 485  *
 486  * If @wait is true, then returns once @func has returned; otherwise
 487  * it returns just before the target cpu calls @func.
 488  *
 489  * You must not call this function with disabled interrupts or from a
 490  * hardware interrupt handler or from a bottom half handler.
 491  */
 492 int smp_call_function(void (*func)(void *), void *info, int wait)
 493 {
 494         preempt_disable();
 495         smp_call_function_many(cpu_online_mask, func, info, wait);
 496         preempt_enable();
 497
 498         return 0;
 499 }
 500 EXPORT_SYMBOL(smp_call_function);
 501
 502 void ipi_call_lock(void)
 503 {
 504         raw_spin_lock(&call_function.lock);
 505 }
 506
 507 void ipi_call_unlock(void)
 508 {
 509         raw_spin_unlock(&call_function.lock);
 510 }
 511
 512 void ipi_call_lock_irq(void)
 513 {
 514         raw_spin_lock_irq(&call_function.lock);
 515 }
 516
 517 void ipi_call_unlock_irq(void)
 518 {
 519         raw_spin_unlock_irq(&call_function.lock);
 520 }