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 static DECLARE_MUTEX(stopmachine_mutex);
  33
  34 static int stopmachine(void *cpu)
  35 {
  36         int irqs_disabled = 0;
  37         int prepared = 0;
  38
  39         set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
  40
  41         /* Ack: we are alive */
  42         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
  43         atomic_inc(&stopmachine_thread_ack);
  44
  45         /* Simple state machine */
  46         while (stopmachine_state != STOPMACHINE_EXIT) {
  47                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
  48                     && !irqs_disabled) {
  49                         local_irq_disable();
  50                         hard_irq_disable();
  51                         irqs_disabled = 1;
  52                         /* Ack: irqs disabled. */
  53                         smp_mb(); /* Must read state first. */
  54                         atomic_inc(&stopmachine_thread_ack);
  55                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  56                            && !prepared) {
  57                         /* Everyone is in place, hold CPU. */
  58                         preempt_disable();
  59                         prepared = 1;
  60                         smp_mb(); /* Must read state first. */
  61                         atomic_inc(&stopmachine_thread_ack);
  62                 }
  63                 /* Yield in first stage: migration threads need to
  64                  * help our sisters onto their CPUs. */
  65                 if (!prepared && !irqs_disabled)
  66                         yield();
  67                 else
  68                         cpu_relax();
  69         }
  70
  71         /* Ack: we are exiting. */
  72         smp_mb(); /* Must read state first. */
  73         atomic_inc(&stopmachine_thread_ack);
  74
  75         if (irqs_disabled)
  76                 local_irq_enable();
  77         if (prepared)
  78                 preempt_enable();
  79
  80         return 0;
  81 }
  82
  83 /* Change the thread state */
  84 static void stopmachine_set_state(enum stopmachine_state state)
  85 {
  86         atomic_set(&stopmachine_thread_ack, 0);
  87         smp_wmb();
  88         stopmachine_state = state;
  89         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  90                 cpu_relax();
  91 }
  92
  93 static int stop_machine(void)
  94 {
  95         int i, ret = 0;
  96         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
  97
  98         /* One high-prio thread per cpu.  We'll do this one. */
  99         sched_setscheduler(current, SCHED_FIFO, &param);
 100
 101         atomic_set(&stopmachine_thread_ack, 0);
 102         stopmachine_num_threads = 0;
 103         stopmachine_state = STOPMACHINE_WAIT;
 104
 105         for_each_online_cpu(i) {
 106                 if (i == raw_smp_processor_id())
 107                         continue;
 108                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 109                 if (ret < 0)
 110                         break;
 111                 stopmachine_num_threads++;
 112         }
 113
 114         /* Wait for them all to come to life. */
 115         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 116                 yield();
 117
 118         /* If some failed, kill them all. */
 119         if (ret < 0) {
 120                 stopmachine_set_state(STOPMACHINE_EXIT);
 121                 return ret;
 122         }
 123
 124         /* Now they are all started, make them hold the CPUs, ready. */
 125         preempt_disable();
 126         stopmachine_set_state(STOPMACHINE_PREPARE);
 127
 128         /* Make them disable irqs. */
 129         local_irq_disable();
 130         hard_irq_disable();
 131         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 132
 133         return 0;
 134 }
 135
 136 static void restart_machine(void)
 137 {
 138         stopmachine_set_state(STOPMACHINE_EXIT);
 139         local_irq_enable();
 140         preempt_enable_no_resched();
 141 }
 142
 143 struct stop_machine_data
 144 {
 145         int (*fn)(void *);
 146         void *data;
 147         struct completion done;
 148 };
 149
 150 static int do_stop(void *_smdata)
 151 {
 152         struct stop_machine_data *smdata = _smdata;
 153         int ret;
 154
 155         ret = stop_machine();
 156         if (ret == 0) {
 157                 ret = smdata->fn(smdata->data);
 158                 restart_machine();
 159         }
 160
 161         /* We're done: you can kthread_stop us now */
 162         complete(&smdata->done);
 163
 164         /* Wait for kthread_stop */
 165         set_current_state(TASK_INTERRUPTIBLE);
 166         while (!kthread_should_stop()) {
 167                 schedule();
 168                 set_current_state(TASK_INTERRUPTIBLE);
 169         }
 170         __set_current_state(TASK_RUNNING);
 171         return ret;
 172 }
 173
 174 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 175                                        unsigned int cpu)
 176 {
 177         struct stop_machine_data smdata;
 178         struct task_struct *p;
 179
 180         smdata.fn = fn;
 181         smdata.data = data;
 182         init_completion(&smdata.done);
 183
 184         down(&stopmachine_mutex);
 185
 186         /* If they don't care which CPU fn runs on, bind to any online one. */
 187         if (cpu == NR_CPUS)
 188                 cpu = raw_smp_processor_id();
 189
 190         p = kthread_create(do_stop, &smdata, "kstopmachine");
 191         if (!IS_ERR(p)) {
 192                 kthread_bind(p, cpu);
 193                 wake_up_process(p);
 194                 wait_for_completion(&smdata.done);
 195         }
 196         up(&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         lock_cpu_hotplug();
 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         unlock_cpu_hotplug();
 213
 214         return ret;
 215 }
 216 EXPORT_SYMBOL_GPL(stop_machine_run);