kernel/stop_machine.c

   1 /* Copyright 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/semaphore.h>
  15 #include <asm/uaccess.h>
  16
  17 /* Since we effect priority and affinity (both of which are visible
  18  * to, and settable by outside processes) we do indirection via a
  19  * kthread. */
  20
  21 /* Thread to stop each CPU in user context. */
  22 enum stopmachine_state {
  23         STOPMACHINE_WAIT,
  24         STOPMACHINE_PREPARE,
  25         STOPMACHINE_DISABLE_IRQ,
  26         STOPMACHINE_EXIT,
  27 };
  28
  29 static enum stopmachine_state stopmachine_state;
  30 static unsigned int stopmachine_num_threads;
  31 static atomic_t stopmachine_thread_ack;
  32
  33 static int stopmachine(void *cpu)
  34 {
  35         int irqs_disabled = 0;
  36         int prepared = 0;
  37
  38         set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
  39
  40         /* Ack: we are alive */
  41         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
  42         atomic_inc(&stopmachine_thread_ack);
  43
  44         /* Simple state machine */
  45         while (stopmachine_state != STOPMACHINE_EXIT) {
  46                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
  47                     && !irqs_disabled) {
  48                         local_irq_disable();
  49                         hard_irq_disable();
  50                         irqs_disabled = 1;
  51                         /* Ack: irqs disabled. */
  52                         smp_mb(); /* Must read state first. */
  53                         atomic_inc(&stopmachine_thread_ack);
  54                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  55                            && !prepared) {
  56                         /* Everyone is in place, hold CPU. */
  57                         preempt_disable();
  58                         prepared = 1;
  59                         smp_mb(); /* Must read state first. */
  60                         atomic_inc(&stopmachine_thread_ack);
  61                 }
  62                 /* Yield in first stage: migration threads need to
  63                  * help our sisters onto their CPUs. */
  64                 if (!prepared && !irqs_disabled)
  65                         yield();
  66                 else
  67                         cpu_relax();
  68         }
  69
  70         /* Ack: we are exiting. */
  71         smp_mb(); /* Must read state first. */
  72         atomic_inc(&stopmachine_thread_ack);
  73
  74         if (irqs_disabled)
  75                 local_irq_enable();
  76         if (prepared)
  77                 preempt_enable();
  78
  79         return 0;
  80 }
  81
  82 /* Change the thread state */
  83 static void stopmachine_set_state(enum stopmachine_state state)
  84 {
  85         atomic_set(&stopmachine_thread_ack, 0);
  86         smp_wmb();
  87         stopmachine_state = state;
  88         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  89                 cpu_relax();
  90 }
  91
  92 static int stop_machine(void)
  93 {
  94         int i, ret = 0;
  95
  96         atomic_set(&stopmachine_thread_ack, 0);
  97         stopmachine_num_threads = 0;
  98         stopmachine_state = STOPMACHINE_WAIT;
  99
 100         for_each_online_cpu(i) {
 101                 if (i == raw_smp_processor_id())
 102                         continue;
 103                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 104                 if (ret < 0)
 105                         break;
 106                 stopmachine_num_threads++;
 107         }
 108
 109         /* Wait for them all to come to life. */
 110         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 111                 yield();
 112
 113         /* If some failed, kill them all. */
 114         if (ret < 0) {
 115                 stopmachine_set_state(STOPMACHINE_EXIT);
 116                 return ret;
 117         }
 118
 119         /* Now they are all started, make them hold the CPUs, ready. */
 120         preempt_disable();
 121         stopmachine_set_state(STOPMACHINE_PREPARE);
 122
 123         /* Make them disable irqs. */
 124         local_irq_disable();
 125         hard_irq_disable();
 126         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 127
 128         return 0;
 129 }
 130
 131 static void restart_machine(void)
 132 {
 133         stopmachine_set_state(STOPMACHINE_EXIT);
 134         local_irq_enable();
 135         preempt_enable_no_resched();
 136 }
 137
 138 struct stop_machine_data
 139 {
 140         int (*fn)(void *);
 141         void *data;
 142         struct completion done;
 143 };
 144
 145 static int do_stop(void *_smdata)
 146 {
 147         struct stop_machine_data *smdata = _smdata;
 148         int ret;
 149
 150         ret = stop_machine();
 151         if (ret == 0) {
 152                 ret = smdata->fn(smdata->data);
 153                 restart_machine();
 154         }
 155
 156         /* We're done: you can kthread_stop us now */
 157         complete(&smdata->done);
 158
 159         /* Wait for kthread_stop */
 160         set_current_state(TASK_INTERRUPTIBLE);
 161         while (!kthread_should_stop()) {
 162                 schedule();
 163                 set_current_state(TASK_INTERRUPTIBLE);
 164         }
 165         __set_current_state(TASK_RUNNING);
 166         return ret;
 167 }
 168
 169 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 170                                        unsigned int cpu)
 171 {
 172         static DEFINE_MUTEX(stopmachine_mutex);
 173         struct stop_machine_data smdata;
 174         struct task_struct *p;
 175
 176         smdata.fn = fn;
 177         smdata.data = data;
 178         init_completion(&smdata.done);
 179
 180         mutex_lock(&stopmachine_mutex);
 181
 182         /* If they don't care which CPU fn runs on, bind to any online one. */
 183         if (cpu == NR_CPUS)
 184                 cpu = raw_smp_processor_id();
 185
 186         p = kthread_create(do_stop, &smdata, "kstopmachine");
 187         if (!IS_ERR(p)) {
 188                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 189
 190                 /* One high-prio thread per cpu.  We'll do this one. */
 191                 sched_setscheduler(p, SCHED_FIFO, &param);
 192                 kthread_bind(p, cpu);
 193                 wake_up_process(p);
 194                 wait_for_completion(&smdata.done);
 195         }
 196         mutex_unlock(&stopmachine_mutex);
 197         return p;
 198 }
 199
 200 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 201 {
 202         struct task_struct *p;
 203         int ret;
 204
 205         /* No CPUs can come up or down during this. */
 206         get_online_cpus();
 207         p = __stop_machine_run(fn, data, cpu);
 208         if (!IS_ERR(p))
 209                 ret = kthread_stop(p);
 210         else
 211                 ret = PTR_ERR(p);
 212         put_online_cpus();
 213
 214         return ret;
 215 }
 216 EXPORT_SYMBOL_GPL(stop_machine_run);