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
  14 static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
  15 static LIST_HEAD(call_function_queue);
  16 __cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
  17
  18 enum {
  19         CSD_FLAG_WAIT           = 0x01,
  20         CSD_FLAG_ALLOC          = 0x02,
  21         CSD_FLAG_LOCK           = 0x04,
  22 };
  23
  24 struct call_function_data {
  25         struct call_single_data csd;
  26         spinlock_t lock;
  27         unsigned int refs;
  28         struct rcu_head rcu_head;
  29         unsigned long cpumask_bits[];
  30 };
  31
  32 struct call_single_queue {
  33         struct list_head list;
  34         spinlock_t lock;
  35 };
  36
  37 static int __cpuinit init_call_single_data(void)
  38 {
  39         int i;
  40
  41         for_each_possible_cpu(i) {
  42                 struct call_single_queue *q = &per_cpu(call_single_queue, i);
  43
  44                 spin_lock_init(&q->lock);
  45                 INIT_LIST_HEAD(&q->list);
  46         }
  47         return 0;
  48 }
  49 early_initcall(init_call_single_data);
  50
  51 static void csd_flag_wait(struct call_single_data *data)
  52 {
  53         /* Wait for response */
  54         do {
  55                 if (!(data->flags & CSD_FLAG_WAIT))
  56                         break;
  57                 cpu_relax();
  58         } while (1);
  59 }
  60
  61 /*
  62  * Insert a previously allocated call_single_data element for execution
  63  * on the given CPU. data must already have ->func, ->info, and ->flags set.
  64  */
  65 static void generic_exec_single(int cpu, struct call_single_data *data)
  66 {
  67         struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
  68         int wait = data->flags & CSD_FLAG_WAIT, ipi;
  69         unsigned long flags;
  70
  71         spin_lock_irqsave(&dst->lock, flags);
  72         ipi = list_empty(&dst->list);
  73         list_add_tail(&data->list, &dst->list);
  74         spin_unlock_irqrestore(&dst->lock, flags);
  75
  76         /*
  77          * Make the list addition visible before sending the ipi.
  78          */
  79         smp_mb();
  80
  81         if (ipi)
  82                 arch_send_call_function_single_ipi(cpu);
  83
  84         if (wait)
  85                 csd_flag_wait(data);
  86 }
  87
  88 static void rcu_free_call_data(struct rcu_head *head)
  89 {
  90         struct call_function_data *data;
  91
  92         data = container_of(head, struct call_function_data, rcu_head);
  93
  94         kfree(data);
  95 }
  96
  97 /*
  98  * Invoked by arch to handle an IPI for call function. Must be called with
  99  * interrupts disabled.
 100  */
 101 void generic_smp_call_function_interrupt(void)
 102 {
 103         struct call_function_data *data;
 104         int cpu = get_cpu();
 105
 106         /*
 107          * It's ok to use list_for_each_rcu() here even though we may delete
 108          * 'pos', since list_del_rcu() doesn't clear ->next
 109          */
 110         rcu_read_lock();
 111         list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
 112                 int refs;
 113
 114                 if (!cpumask_test_cpu(cpu, to_cpumask(data->cpumask_bits)))
 115                         continue;
 116
 117                 data->csd.func(data->csd.info);
 118
 119                 spin_lock(&data->lock);
 120                 cpumask_clear_cpu(cpu, to_cpumask(data->cpumask_bits));
 121                 WARN_ON(data->refs == 0);
 122                 data->refs--;
 123                 refs = data->refs;
 124                 spin_unlock(&data->lock);
 125
 126                 if (refs)
 127                         continue;
 128
 129                 spin_lock(&call_function_lock);
 130                 list_del_rcu(&data->csd.list);
 131                 spin_unlock(&call_function_lock);
 132
 133                 if (data->csd.flags & CSD_FLAG_WAIT) {
 134                         /*
 135                          * serialize stores to data with the flag clear
 136                          * and wakeup
 137                          */
 138                         smp_wmb();
 139                         data->csd.flags &= ~CSD_FLAG_WAIT;
 140                 }
 141                 if (data->csd.flags & CSD_FLAG_ALLOC)
 142                         call_rcu(&data->rcu_head, rcu_free_call_data);
 143         }
 144         rcu_read_unlock();
 145
 146         put_cpu();
 147 }
 148
 149 /*
 150  * Invoked by arch to handle an IPI for call function single. Must be called
 151  * from the arch with interrupts disabled.
 152  */
 153 void generic_smp_call_function_single_interrupt(void)
 154 {
 155         struct call_single_queue *q = &__get_cpu_var(call_single_queue);
 156         LIST_HEAD(list);
 157
 158         /*
 159          * Need to see other stores to list head for checking whether
 160          * list is empty without holding q->lock
 161          */
 162         smp_read_barrier_depends();
 163         while (!list_empty(&q->list)) {
 164                 unsigned int data_flags;
 165
 166                 spin_lock(&q->lock);
 167                 list_replace_init(&q->list, &list);
 168                 spin_unlock(&q->lock);
 169
 170                 while (!list_empty(&list)) {
 171                         struct call_single_data *data;
 172
 173                         data = list_entry(list.next, struct call_single_data,
 174                                                 list);
 175                         list_del(&data->list);
 176
 177                         /*
 178                          * 'data' can be invalid after this call if
 179                          * flags == 0 (when called through
 180                          * generic_exec_single(), so save them away before
 181                          * making the call.
 182                          */
 183                         data_flags = data->flags;
 184
 185                         data->func(data->info);
 186
 187                         if (data_flags & CSD_FLAG_WAIT) {
 188                                 smp_wmb();
 189                                 data->flags &= ~CSD_FLAG_WAIT;
 190                         } else if (data_flags & CSD_FLAG_LOCK) {
 191                                 smp_wmb();
 192                                 data->flags &= ~CSD_FLAG_LOCK;
 193                         } else if (data_flags & CSD_FLAG_ALLOC)
 194                                 kfree(data);
 195                 }
 196                 /*
 197                  * See comment on outer loop
 198                  */
 199                 smp_read_barrier_depends();
 200         }
 201 }
 202
 203 static DEFINE_PER_CPU(struct call_single_data, csd_data);
 204
 205 /*
 206  * smp_call_function_single - Run a function on a specific CPU
 207  * @func: The function to run. This must be fast and non-blocking.
 208  * @info: An arbitrary pointer to pass to the function.
 209  * @wait: If true, wait until function has completed on other CPUs.
 210  *
 211  * Returns 0 on success, else a negative status code. Note that @wait
 212  * will be implicitly turned on in case of allocation failures, since
 213  * we fall back to on-stack allocation.
 214  */
 215 int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 216                              int wait)
 217 {
 218         struct call_single_data d;
 219         unsigned long flags;
 220         /* prevent preemption and reschedule on another processor,
 221            as well as CPU removal */
 222         int me = get_cpu();
 223         int err = 0;
 224
 225         /* Can deadlock when called with interrupts disabled */
 226         WARN_ON(irqs_disabled());
 227
 228         if (cpu == me) {
 229                 local_irq_save(flags);
 230                 func(info);
 231                 local_irq_restore(flags);
 232         } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
 233                 struct call_single_data *data;
 234
 235                 if (!wait) {
 236                         /*
 237                          * We are calling a function on a single CPU
 238                          * and we are not going to wait for it to finish.
 239                          * We first try to allocate the data, but if we
 240                          * fail, we fall back to use a per cpu data to pass
 241                          * the information to that CPU. Since all callers
 242                          * of this code will use the same data, we must
 243                          * synchronize the callers to prevent a new caller
 244                          * from corrupting the data before the callee
 245                          * can access it.
 246                          *
 247                          * The CSD_FLAG_LOCK is used to let us know when
 248                          * the IPI handler is done with the data.
 249                          * The first caller will set it, and the callee
 250                          * will clear it. The next caller must wait for
 251                          * it to clear before we set it again. This
 252                          * will make sure the callee is done with the
 253                          * data before a new caller will use it.
 254                          */
 255                         data = kmalloc(sizeof(*data), GFP_ATOMIC);
 256                         if (data)
 257                                 data->flags = CSD_FLAG_ALLOC;
 258                         else {
 259                                 data = &per_cpu(csd_data, me);
 260                                 while (data->flags & CSD_FLAG_LOCK)
 261                                         cpu_relax();
 262                                 data->flags = CSD_FLAG_LOCK;
 263                         }
 264                 } else {
 265                         data = &d;
 266                         data->flags = CSD_FLAG_WAIT;
 267                 }
 268
 269                 data->func = func;
 270                 data->info = info;
 271                 generic_exec_single(cpu, data);
 272         } else {
 273                 err = -ENXIO;   /* CPU not online */
 274         }
 275
 276         put_cpu();
 277         return err;
 278 }
 279 EXPORT_SYMBOL(smp_call_function_single);
 280
 281 /**
 282  * __smp_call_function_single(): Run a function on another CPU
 283  * @cpu: The CPU to run on.
 284  * @data: Pre-allocated and setup data structure
 285  *
 286  * Like smp_call_function_single(), but allow caller to pass in a pre-allocated
 287  * data structure. Useful for embedding @data inside other structures, for
 288  * instance.
 289  *
 290  */
 291 void __smp_call_function_single(int cpu, struct call_single_data *data)
 292 {
 293         /* Can deadlock when called with interrupts disabled */
 294         WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
 295
 296         generic_exec_single(cpu, data);
 297 }
 298
 299 /* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
 300 #ifndef arch_send_call_function_ipi_mask
 301 #define arch_send_call_function_ipi_mask(maskp) \
 302         arch_send_call_function_ipi(*(maskp))
 303 #endif
 304
 305 /**
 306  * smp_call_function_many(): Run a function on a set of other CPUs.
 307  * @mask: The set of cpus to run on (only runs on online subset).
 308  * @func: The function to run. This must be fast and non-blocking.
 309  * @info: An arbitrary pointer to pass to the function.
 310  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 311  *
 312  * If @wait is true, then returns once @func has returned. Note that @wait
 313  * will be implicitly turned on in case of allocation failures, since
 314  * we fall back to on-stack allocation.
 315  *
 316  * You must not call this function with disabled interrupts or from a
 317  * hardware interrupt handler or from a bottom half handler. Preemption
 318  * must be disabled when calling this function.
 319  */
 320 void smp_call_function_many(const struct cpumask *mask,
 321                             void (*func)(void *), void *info,
 322                             bool wait)
 323 {
 324         struct call_function_data *data;
 325         unsigned long flags;
 326         int cpu, next_cpu;
 327
 328         /* Can deadlock when called with interrupts disabled */
 329         WARN_ON(irqs_disabled());
 330
 331         /* So, what's a CPU they want?  Ignoring this one. */
 332         cpu = cpumask_first_and(mask, cpu_online_mask);
 333         if (cpu == smp_processor_id())
 334                 cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 335         /* No online cpus?  We're done. */
 336         if (cpu >= nr_cpu_ids)
 337                 return;
 338
 339         /* Do we have another CPU which isn't us? */
 340         next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 341         if (next_cpu == smp_processor_id())
 342                 next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
 343
 344         /* Fastpath: do that cpu by itself. */
 345         if (next_cpu >= nr_cpu_ids) {
 346                 smp_call_function_single(cpu, func, info, wait);
 347                 return;
 348         }
 349
 350         data = kmalloc(sizeof(*data) + cpumask_size(), GFP_ATOMIC);
 351         if (unlikely(!data)) {
 352                 /* Slow path. */
 353                 for_each_online_cpu(cpu) {
 354                         if (cpu == smp_processor_id())
 355                                 continue;
 356                         if (cpumask_test_cpu(cpu, mask))
 357                                 smp_call_function_single(cpu, func, info, wait);
 358                 }
 359                 return;
 360         }
 361
 362         spin_lock_init(&data->lock);
 363         data->csd.flags = CSD_FLAG_ALLOC;
 364         if (wait)
 365                 data->csd.flags |= CSD_FLAG_WAIT;
 366         data->csd.func = func;
 367         data->csd.info = info;
 368         cpumask_and(to_cpumask(data->cpumask_bits), mask, cpu_online_mask);
 369         cpumask_clear_cpu(smp_processor_id(), to_cpumask(data->cpumask_bits));
 370         data->refs = cpumask_weight(to_cpumask(data->cpumask_bits));
 371
 372         spin_lock_irqsave(&call_function_lock, flags);
 373         list_add_tail_rcu(&data->csd.list, &call_function_queue);
 374         spin_unlock_irqrestore(&call_function_lock, flags);
 375
 376         /*
 377          * Make the list addition visible before sending the ipi.
 378          */
 379         smp_mb();
 380
 381         /* Send a message to all CPUs in the map */
 382         arch_send_call_function_ipi_mask(to_cpumask(data->cpumask_bits));
 383
 384         /* optionally wait for the CPUs to complete */
 385         if (wait)
 386                 csd_flag_wait(&data->csd);
 387 }
 388 EXPORT_SYMBOL(smp_call_function_many);
 389
 390 /**
 391  * smp_call_function(): Run a function on all other CPUs.
 392  * @func: The function to run. This must be fast and non-blocking.
 393  * @info: An arbitrary pointer to pass to the function.
 394  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 395  *
 396  * Returns 0.
 397  *
 398  * If @wait is true, then returns once @func has returned; otherwise
 399  * it returns just before the target cpu calls @func. In case of allocation
 400  * failure, @wait will be implicitly turned on.
 401  *
 402  * You must not call this function with disabled interrupts or from a
 403  * hardware interrupt handler or from a bottom half handler.
 404  */
 405 int smp_call_function(void (*func)(void *), void *info, int wait)
 406 {
 407         preempt_disable();
 408         smp_call_function_many(cpu_online_mask, func, info, wait);
 409         preempt_enable();
 410         return 0;
 411 }
 412 EXPORT_SYMBOL(smp_call_function);
 413
 414 void ipi_call_lock(void)
 415 {
 416         spin_lock(&call_function_lock);
 417 }
 418
 419 void ipi_call_unlock(void)
 420 {
 421         spin_unlock(&call_function_lock);
 422 }
 423
 424 void ipi_call_lock_irq(void)
 425 {
 426         spin_lock_irq(&call_function_lock);
 427 }
 428
 429 void ipi_call_unlock_irq(void)
 430 {
 431         spin_unlock_irq(&call_function_lock);
 432 }