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