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