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