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