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                 }
 139                 if (data->csd.flags & CSD_FLAG_ALLOC)
 140                         call_rcu(&data->rcu_head, rcu_free_call_data);
 141         }
 142         rcu_read_unlock();
 143
 144         put_cpu();
 145 }
 146
 147 /*
 148  * Invoked by arch to handle an IPI for call function single. Must be called
 149  * from the arch with interrupts disabled.
 150  */
 151 void generic_smp_call_function_single_interrupt(void)
 152 {
 153         struct call_single_queue *q = &__get_cpu_var(call_single_queue);
 154         LIST_HEAD(list);
 155
 156         /*
 157          * Need to see other stores to list head for checking whether
 158          * list is empty without holding q->lock
 159          */
 160         smp_mb();
 161         while (!list_empty(&q->list)) {
 162                 unsigned int data_flags;
 163
 164                 spin_lock(&q->lock);
 165                 list_replace_init(&q->list, &list);
 166                 spin_unlock(&q->lock);
 167
 168                 while (!list_empty(&list)) {
 169                         struct call_single_data *data;
 170
 171                         data = list_entry(list.next, struct call_single_data,
 172                                                 list);
 173                         list_del(&data->list);
 174
 175                         /*
 176                          * 'data' can be invalid after this call if
 177                          * flags == 0 (when called through
 178                          * generic_exec_single(), so save them away before
 179                          * making the call.
 180                          */
 181                         data_flags = data->flags;
 182
 183                         data->func(data->info);
 184
 185                         if (data_flags & CSD_FLAG_WAIT) {
 186                                 smp_wmb();
 187                                 data->flags &= ~CSD_FLAG_WAIT;
 188                         } else if (data_flags & CSD_FLAG_ALLOC)
 189                                 kfree(data);
 190                 }
 191                 /*
 192                  * See comment on outer loop
 193                  */
 194                 smp_mb();
 195         }
 196 }
 197
 198 /*
 199  * smp_call_function_single - Run a function on a specific CPU
 200  * @func: The function to run. This must be fast and non-blocking.
 201  * @info: An arbitrary pointer to pass to the function.
 202  * @wait: If true, wait until function has completed on other CPUs.
 203  *
 204  * Returns 0 on success, else a negative status code. Note that @wait
 205  * will be implicitly turned on in case of allocation failures, since
 206  * we fall back to on-stack allocation.
 207  */
 208 int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 209                              int wait)
 210 {
 211         struct call_single_data d;
 212         unsigned long flags;
 213         /* prevent preemption and reschedule on another processor */
 214         int me = get_cpu();
 215
 216         /* Can deadlock when called with interrupts disabled */
 217         WARN_ON(irqs_disabled());
 218
 219         if (cpu == me) {
 220                 local_irq_save(flags);
 221                 func(info);
 222                 local_irq_restore(flags);
 223         } else {
 224                 struct call_single_data *data = NULL;
 225
 226                 if (!wait) {
 227                         data = kmalloc(sizeof(*data), GFP_ATOMIC);
 228                         if (data)
 229                                 data->flags = CSD_FLAG_ALLOC;
 230                 }
 231                 if (!data) {
 232                         data = &d;
 233                         data->flags = CSD_FLAG_WAIT;
 234                 }
 235
 236                 data->func = func;
 237                 data->info = info;
 238                 generic_exec_single(cpu, data);
 239         }
 240
 241         put_cpu();
 242         return 0;
 243 }
 244 EXPORT_SYMBOL(smp_call_function_single);
 245
 246 /**
 247  * __smp_call_function_single(): Run a function on another CPU
 248  * @cpu: The CPU to run on.
 249  * @data: Pre-allocated and setup data structure
 250  *
 251  * Like smp_call_function_single(), but allow caller to pass in a pre-allocated
 252  * data structure. Useful for embedding @data inside other structures, for
 253  * instance.
 254  *
 255  */
 256 void __smp_call_function_single(int cpu, struct call_single_data *data)
 257 {
 258         /* Can deadlock when called with interrupts disabled */
 259         WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
 260
 261         generic_exec_single(cpu, data);
 262 }
 263
 264 /* Dummy function */
 265 static void quiesce_dummy(void *unused)
 266 {
 267 }
 268
 269 /*
 270  * Ensure stack based data used in call function mask is safe to free.
 271  *
 272  * This is needed by smp_call_function_mask when using on-stack data, because
 273  * a single call function queue is shared by all CPUs, and any CPU may pick up
 274  * the data item on the queue at any time before it is deleted. So we need to
 275  * ensure that all CPUs have transitioned through a quiescent state after
 276  * this call.
 277  *
 278  * This is a very slow function, implemented by sending synchronous IPIs to
 279  * all possible CPUs. For this reason, we have to alloc data rather than use
 280  * stack based data even in the case of synchronous calls. The stack based
 281  * data is then just used for deadlock/oom fallback which will be very rare.
 282  *
 283  * If a faster scheme can be made, we could go back to preferring stack based
 284  * data -- the data allocation/free is non-zero cost.
 285  */
 286 static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
 287 {
 288         struct call_single_data data;
 289         int cpu;
 290
 291         data.func = quiesce_dummy;
 292         data.info = NULL;
 293
 294         for_each_cpu_mask(cpu, mask) {
 295                 data.flags = CSD_FLAG_WAIT;
 296                 generic_exec_single(cpu, &data);
 297         }
 298 }
 299
 300 /**
 301  * smp_call_function_mask(): Run a function on a set of other CPUs.
 302  * @mask: The set of cpus to run on.
 303  * @func: The function to run. This must be fast and non-blocking.
 304  * @info: An arbitrary pointer to pass to the function.
 305  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 306  *
 307  * Returns 0 on success, else a negative status code.
 308  *
 309  * If @wait is true, then returns once @func has returned. Note that @wait
 310  * will be implicitly turned on in case of allocation failures, since
 311  * we fall back to on-stack allocation.
 312  *
 313  * You must not call this function with disabled interrupts or from a
 314  * hardware interrupt handler or from a bottom half handler. Preemption
 315  * must be disabled when calling this function.
 316  */
 317 int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
 318                            int wait)
 319 {
 320         struct call_function_data d;
 321         struct call_function_data *data = NULL;
 322         cpumask_t allbutself;
 323         unsigned long flags;
 324         int cpu, num_cpus;
 325         int slowpath = 0;
 326
 327         /* Can deadlock when called with interrupts disabled */
 328         WARN_ON(irqs_disabled());
 329
 330         cpu = smp_processor_id();
 331         allbutself = cpu_online_map;
 332         cpu_clear(cpu, allbutself);
 333         cpus_and(mask, mask, allbutself);
 334         num_cpus = cpus_weight(mask);
 335
 336         /*
 337          * If zero CPUs, return. If just a single CPU, turn this request
 338          * into a targetted single call instead since it's faster.
 339          */
 340         if (!num_cpus)
 341                 return 0;
 342         else if (num_cpus == 1) {
 343                 cpu = first_cpu(mask);
 344                 return smp_call_function_single(cpu, func, info, wait);
 345         }
 346
 347         data = kmalloc(sizeof(*data), GFP_ATOMIC);
 348         if (data) {
 349                 data->csd.flags = CSD_FLAG_ALLOC;
 350                 if (wait)
 351                         data->csd.flags |= CSD_FLAG_WAIT;
 352         } else {
 353                 data = &d;
 354                 data->csd.flags = CSD_FLAG_WAIT;
 355                 wait = 1;
 356                 slowpath = 1;
 357         }
 358
 359         spin_lock_init(&data->lock);
 360         data->csd.func = func;
 361         data->csd.info = info;
 362         data->refs = num_cpus;
 363         data->cpumask = mask;
 364
 365         spin_lock_irqsave(&call_function_lock, flags);
 366         list_add_tail_rcu(&data->csd.list, &call_function_queue);
 367         spin_unlock_irqrestore(&call_function_lock, flags);
 368
 369         /* Send a message to all CPUs in the map */
 370         arch_send_call_function_ipi(mask);
 371
 372         /* optionally wait for the CPUs to complete */
 373         if (wait) {
 374                 csd_flag_wait(&data->csd);
 375                 if (unlikely(slowpath))
 376                         smp_call_function_mask_quiesce_stack(mask);
 377         }
 378
 379         return 0;
 380 }
 381 EXPORT_SYMBOL(smp_call_function_mask);
 382
 383 /**
 384  * smp_call_function(): Run a function on all other CPUs.
 385  * @func: The function to run. This must be fast and non-blocking.
 386  * @info: An arbitrary pointer to pass to the function.
 387  * @wait: If true, wait (atomically) until function has completed on other CPUs.
 388  *
 389  * Returns 0 on success, else a negative status code.
 390  *
 391  * If @wait is true, then returns once @func has returned; otherwise
 392  * it returns just before the target cpu calls @func. In case of allocation
 393  * failure, @wait will be implicitly turned on.
 394  *
 395  * You must not call this function with disabled interrupts or from a
 396  * hardware interrupt handler or from a bottom half handler.
 397  */
 398 int smp_call_function(void (*func)(void *), void *info, int wait)
 399 {
 400         int ret;
 401
 402         preempt_disable();
 403         ret = smp_call_function_mask(cpu_online_map, func, info, wait);
 404         preempt_enable();
 405         return ret;
 406 }
 407 EXPORT_SYMBOL(smp_call_function);
 408
 409 void ipi_call_lock(void)
 410 {
 411         spin_lock(&call_function_lock);
 412 }
 413
 414 void ipi_call_unlock(void)
 415 {
 416         spin_unlock(&call_function_lock);
 417 }
 418
 419 void ipi_call_lock_irq(void)
 420 {
 421         spin_lock_irq(&call_function_lock);
 422 }
 423
 424 void ipi_call_unlock_irq(void)
 425 {
 426         spin_unlock_irq(&call_function_lock);
 427 }