kernel/stop_machine.c

   1 /* Copyright 2008, 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation.
   2  * GPL v2 and any later version.
   3  */
   4 #include <linux/cpu.h>
   5 #include <linux/err.h>
   6 #include <linux/kthread.h>
   7 #include <linux/module.h>
   8 #include <linux/sched.h>
   9 #include <linux/stop_machine.h>
  10 #include <linux/syscalls.h>
  11 #include <linux/interrupt.h>
  12
  13 #include <asm/atomic.h>
  14 #include <asm/uaccess.h>
  15
  16 /* This controls the threads on each CPU. */
  17 enum stopmachine_state {
  18         /* Dummy starting state for thread. */
  19         STOPMACHINE_NONE,
  20         /* Awaiting everyone to be scheduled. */
  21         STOPMACHINE_PREPARE,
  22         /* Disable interrupts. */
  23         STOPMACHINE_DISABLE_IRQ,
  24         /* Run the function */
  25         STOPMACHINE_RUN,
  26         /* Exit */
  27         STOPMACHINE_EXIT,
  28 };
  29 static enum stopmachine_state state;
  30
  31 struct stop_machine_data {
  32         int (*fn)(void *);
  33         void *data;
  34         int fnret;
  35 };
  36
  37 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
  38 static unsigned int num_threads;
  39 static atomic_t thread_ack;
  40 static struct completion finished;
  41 static DEFINE_MUTEX(lock);
  42
  43 static void set_state(enum stopmachine_state newstate)
  44 {
  45         /* Reset ack counter. */
  46         atomic_set(&thread_ack, num_threads);
  47         smp_wmb();
  48         state = newstate;
  49 }
  50
  51 /* Last one to ack a state moves to the next state. */
  52 static void ack_state(void)
  53 {
  54         if (atomic_dec_and_test(&thread_ack)) {
  55                 /* If we're the last one to ack the EXIT, we're finished. */
  56                 if (state == STOPMACHINE_EXIT)
  57                         complete(&finished);
  58                 else
  59                         set_state(state + 1);
  60         }
  61 }
  62
  63 /* This is the actual thread which stops the CPU.  It exits by itself rather
  64  * than waiting for kthread_stop(), because it's easier for hotplug CPU. */
  65 static int stop_cpu(struct stop_machine_data *smdata)
  66 {
  67         enum stopmachine_state curstate = STOPMACHINE_NONE;
  68
  69         /* Simple state machine */
  70         do {
  71                 /* Chill out and ensure we re-read stopmachine_state. */
  72                 cpu_relax();
  73                 if (state != curstate) {
  74                         curstate = state;
  75                         switch (curstate) {
  76                         case STOPMACHINE_DISABLE_IRQ:
  77                                 local_irq_disable();
  78                                 hard_irq_disable();
  79                                 break;
  80                         case STOPMACHINE_RUN:
  81                                 /* |= allows error detection if functions on
  82                                  * multiple CPUs. */
  83                                 smdata->fnret |= smdata->fn(smdata->data);
  84                                 break;
  85                         default:
  86                                 break;
  87                         }
  88                         ack_state();
  89                 }
  90         } while (curstate != STOPMACHINE_EXIT);
  91
  92         local_irq_enable();
  93         do_exit(0);
  94 }
  95
  96 /* Callback for CPUs which aren't supposed to do anything. */
  97 static int chill(void *unused)
  98 {
  99         return 0;
 100 }
 101
 102 int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
 103 {
 104         int i, err;
 105         struct stop_machine_data active, idle;
 106         struct task_struct **threads;
 107
 108         active.fn = fn;
 109         active.data = data;
 110         active.fnret = 0;
 111         idle.fn = chill;
 112         idle.data = NULL;
 113
 114         /* This could be too big for stack on large machines. */
 115         threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
 116         if (!threads)
 117                 return -ENOMEM;
 118
 119         /* Set up initial state. */
 120         mutex_lock(&lock);
 121         init_completion(&finished);
 122         num_threads = num_online_cpus();
 123         set_state(STOPMACHINE_PREPARE);
 124
 125         for_each_online_cpu(i) {
 126                 struct stop_machine_data *smdata = &idle;
 127                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 128
 129                 if (!cpus) {
 130                         if (i == first_cpu(cpu_online_map))
 131                                 smdata = &active;
 132                 } else {
 133                         if (cpu_isset(i, *cpus))
 134                                 smdata = &active;
 135                 }
 136
 137                 threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
 138                                             i);
 139                 if (IS_ERR(threads[i])) {
 140                         err = PTR_ERR(threads[i]);
 141                         threads[i] = NULL;
 142                         goto kill_threads;
 143                 }
 144
 145                 /* Place it onto correct cpu. */
 146                 kthread_bind(threads[i], i);
 147
 148                 /* Make it highest prio. */
 149                 if (sched_setscheduler_nocheck(threads[i], SCHED_FIFO, &param))
 150                         BUG();
 151         }
 152
 153         /* We've created all the threads.  Wake them all: hold this CPU so one
 154          * doesn't hit this CPU until we're ready. */
 155         get_cpu();
 156         for_each_online_cpu(i)
 157                 wake_up_process(threads[i]);
 158
 159         /* This will release the thread on our CPU. */
 160         put_cpu();
 161         wait_for_completion(&finished);
 162         mutex_unlock(&lock);
 163
 164         kfree(threads);
 165
 166         return active.fnret;
 167
 168 kill_threads:
 169         for_each_online_cpu(i)
 170                 if (threads[i])
 171                         kthread_stop(threads[i]);
 172         mutex_unlock(&lock);
 173
 174         kfree(threads);
 175         return err;
 176 }
 177
 178 int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
 179 {
 180         int ret;
 181
 182         /* No CPUs can come up or down during this. */
 183         get_online_cpus();
 184         ret = __stop_machine(fn, data, cpus);
 185         put_online_cpus();
 186
 187         return ret;
 188 }
 189 EXPORT_SYMBOL_GPL(stop_machine);