kernel/smp.c

   1 /*
   2  * Generic helpers for smp ipi calls
   3  *
   4  * (C) Jens Axboe <jens.axboe@oracle.com> 2008
   5  *
   6  */
   7 #include <linux/init.h>
   8 #include <linux/module.h>
   9 #include <linux/percpu.h>
  10 #include <linux/rcupdate.h>
  11 #include <linux/rculist.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         .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 previous
 100  * function call. For multi-cpu calls its even more interesting as we'll have
 101  * 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 to ->flags
 116          * with any subsequent assignments to other fields of the
 117          * specified call_single_data structure.
 118          */
 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          * ensure we're all done before releasing data
 128          */
 129         smp_mb();
 130         data->flags &= ~CSD_FLAG_LOCK;
 131 }
 132
 133 /*
 134  * Insert a previously allocated call_single_data element for execution
 135  * on the given CPU. data must already have ->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 equipped
 158          * to do the right thing...
 159          */
 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 = get_cpu();
 176
 177         /*
 178          * Ensure entry is visible on call_function_queue after we have
 179          * entered the IPI. See comment in smp_call_function_many.
 180          * If we don't have this, then we may miss an entry on the list
 181          * and never get another IPI to process it.
 182          */
 183         smp_mb();
 184
 185         /*
 186          * It's ok to use list_for_each_rcu() here even though we may delete
 187          * 'pos', since list_del_rcu() doesn't clear ->next
 188          */
 189         list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
 190                 int refs;
 191
 192                 spin_lock(&data->lock);
 193                 if (!cpumask_test_cpu(cpu, data->cpumask)) {
 194                         spin_unlock(&data->lock);
 195                         continue;
 196                 }
 197                 cpumask_clear_cpu(cpu, data->cpumask);
 198                 spin_unlock(&data->lock);
 199
 200                 data->csd.func(data->csd.info);
 201
 202                 spin_lock(&data->lock);
 203                 WARN_ON(data->refs == 0);
 204                 refs = --data->refs;
 205                 if (!refs) {
 206                         spin_lock(&call_function.lock);
 207                         list_del_rcu(&data->csd.list);
 208                         spin_unlock(&call_function.lock);
 209                 }
 210                 spin_unlock(&data->lock);
 211
 212                 if (refs)
 213                         continue;
 214
 215                 csd_unlock(&data->csd);
 216         }
 217
 218         put_cpu();
 219 }
 220
 221 /*
 222  * Invoked by arch to handle an IPI for call function single. Must be called
 223  * from the arch with interrupts disabled.
 224  */
 225 void generic_smp_call_function_single_interrupt(void)
 226 {
 227         struct call_single_queue *q = &__get_cpu_var(call_single_queue);
 228         LIST_HEAD(list);
 229         unsigned int data_flags;
 230
 231         spin_lock(&q->lock);
 232         list_replace_init(&q->list, &list);
 233         spin_unlock(&q->lock);
 234
 235         while (!list_empty(&list)) {
 236                 struct call_single_data *data;
 237
 238                 data = list_entry(list.next, struct call_single_data,
 239                                         list);
 240                 list_del(&data->list);
 241
 242                 /*
 243                  * 'data' can be invalid after this call if
 244                  * flags == 0 (when called through
 245                  * generic_exec_single(), so save them away before
 246                  * 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         /* prevent preemption and reschedule on another processor,
 280            as well as CPU removal */
 281         int me = get_cpu();
 282         int err = 0;
 283
 284         /* Can deadlock when called with interrupts disabled */
 285         WARN_ON(irqs_disabled());
 286
 287         if (cpu == me) {
 288                 local_irq_save(flags);
 289                 func(info);
 290                 local_irq_restore(flags);
 291         } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
 292                 struct call_single_data *data = &d;
 293
 294                 if (!wait)
 295                         data = &__get_cpu_var(csd_data);
 296
 297                 csd_lock(data);
 298
 299                 data->func = func;
 300                 data->info = info;
 301                 generic_exec_single(cpu, data, wait);
 302         } else {
 303                 err = -ENXIO;   /* CPU not online */
 304         }
 305
 306         put_cpu();
 307         return err;
 308 }
 309 EXPORT_SYMBOL(smp_call_function_single);
 310
 311 /**
 312  * __smp_call_function_single(): Run a function on another CPU
 313  * @cpu: The CPU to run on.
 314  * @data: Pre-allocated and setup data structure
 315  *
 316  * Like smp_call_function_single(), but allow caller to pass in a pre-allocated
 317  * data structure. Useful for embedding @data inside other structures, for
 318  * instance.
 319  *
 320  */
 321 void __smp_call_function_single(int cpu, struct call_single_data *data,
 322                                 int wait)
 323 {
 324         csd_lock(data);
 325
 326         /* Can deadlock when called with interrupts disabled */
 327         WARN_ON(wait && irqs_disabled());
 328
 329         generic_exec_single(cpu, data, wait);
 330 }
 331
 332 /* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
 333 #ifndef arch_send_call_function_ipi_mask
 334 #define arch_send_call_function_ipi_mask(maskp) \
 335         arch_send_call_function_ipi(*(maskp))
 336 #endif
 337
 338 /**
 339  * smp_call_function_many(): Run a function on a set of other CPUs.
 340  * @mask: The set of cpus to run on (only runs on online subset).
 341  * @func: The function to run. This must be fast and non-blocking.
 342  * @info: An arbitrary pointer to pass to the function.
 343  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 344  *
 345  * If @wait is true, then returns once @func has returned. Note that @wait
 346  * will be implicitly turned on in case of allocation failures, since
 347  * we fall back to on-stack allocation.
 348  *
 349  * You must not call this function with disabled interrupts or from a
 350  * hardware interrupt handler or from a bottom half handler. Preemption
 351  * must be disabled when calling this function.
 352  */
 353 void smp_call_function_many(const struct cpumask *mask,
 354                             void (*func)(void *), void *info,
 355                             bool wait)
 356 {
 357         struct call_function_data *data;
 358         unsigned long flags;
 359         int cpu, next_cpu, me = smp_processor_id();
 360
 361         /* Can deadlock when called with interrupts disabled */
 362         WARN_ON(irqs_disabled());
 363
 364         /* So, what's a CPU they want?  Ignoring this one. */
 365         cpu = cpumask_first_and(mask, cpu_online_mask);
 366         if (cpu == me)
 367                 cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 368         /* No online cpus?  We're done. */
 369         if (cpu >= nr_cpu_ids)
 370                 return;
 371
 372         /* Do we have another CPU which isn't us? */
 373         next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 374         if (next_cpu == me)
 375                 next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
 376
 377         /* Fastpath: do that cpu by itself. */
 378         if (next_cpu >= nr_cpu_ids) {
 379                 smp_call_function_single(cpu, func, info, wait);
 380                 return;
 381         }
 382
 383         data = &__get_cpu_var(cfd_data);
 384         csd_lock(&data->csd);
 385
 386         spin_lock_irqsave(&data->lock, flags);
 387         data->csd.func = func;
 388         data->csd.info = info;
 389         cpumask_and(data->cpumask, mask, cpu_online_mask);
 390         cpumask_clear_cpu(me, data->cpumask);
 391         data->refs = cpumask_weight(data->cpumask);
 392
 393         spin_lock(&call_function.lock);
 394         /*
 395          * Place entry at the _HEAD_ of the list, so that any cpu still
 396          * observing the entry in generic_smp_call_function_interrupt() will
 397          * not miss any other list entries.
 398          */
 399         list_add_rcu(&data->csd.list, &call_function.queue);
 400         spin_unlock(&call_function.lock);
 401         spin_unlock_irqrestore(&data->lock, flags);
 402
 403         /*
 404          * Make the list addition visible before sending the ipi.
 405          * (IPIs must obey or appear to obey normal Linux cache coherency
 406          * rules -- see comment in generic_exec_single).
 407          */
 408         smp_mb();
 409
 410         /* Send a message to all CPUs in the map */
 411         arch_send_call_function_ipi_mask(data->cpumask);
 412
 413         /* optionally wait for the CPUs to complete */
 414         if (wait)
 415                 csd_lock_wait(&data->csd);
 416 }
 417 EXPORT_SYMBOL(smp_call_function_many);
 418
 419 /**
 420  * smp_call_function(): Run a function on all other CPUs.
 421  * @func: The function to run. This must be fast and non-blocking.
 422  * @info: An arbitrary pointer to pass to the function.
 423  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 424  *
 425  * Returns 0.
 426  *
 427  * If @wait is true, then returns once @func has returned; otherwise
 428  * it returns just before the target cpu calls @func. In case of allocation
 429  * failure, @wait will be implicitly turned on.
 430  *
 431  * You must not call this function with disabled interrupts or from a
 432  * hardware interrupt handler or from a bottom half handler.
 433  */
 434 int smp_call_function(void (*func)(void *), void *info, int wait)
 435 {
 436         preempt_disable();
 437         smp_call_function_many(cpu_online_mask, func, info, wait);
 438         preempt_enable();
 439         return 0;
 440 }
 441 EXPORT_SYMBOL(smp_call_function);
 442
 443 void ipi_call_lock(void)
 444 {
 445         spin_lock(&call_function.lock);
 446 }
 447
 448 void ipi_call_unlock(void)
 449 {
 450         spin_unlock(&call_function.lock);
 451 }
 452
 453 void ipi_call_lock_irq(void)
 454 {
 455         spin_lock_irq(&call_function.lock);
 456 }
 457
 458 void ipi_call_unlock_irq(void)
 459 {
 460         spin_unlock_irq(&call_function.lock);
 461 }