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 <asm/atomic.h>
  12 #include <asm/semaphore.h>
  13 #include <asm/uaccess.h>
  14
  15 /* Since we effect priority and affinity (both of which are visible
  16  * to, and settable by outside processes) we do indirection via a
  17  * kthread. */
  18
  19 /* Thread to stop each CPU in user context. */
  20 enum stopmachine_state {
  21         STOPMACHINE_WAIT,
  22         STOPMACHINE_PREPARE,
  23         STOPMACHINE_DISABLE_IRQ,
  24         STOPMACHINE_EXIT,
  25 };
  26
  27 static enum stopmachine_state stopmachine_state;
  28 static unsigned int stopmachine_num_threads;
  29 static atomic_t stopmachine_thread_ack;
  30 static DECLARE_MUTEX(stopmachine_mutex);
  31
  32 static int stopmachine(void *cpu)
  33 {
  34         int irqs_disabled = 0;
  35         int prepared = 0;
  36
  37         set_cpus_allowed(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                         irqs_disabled = 1;
  49                         /* Ack: irqs disabled. */
  50                         smp_mb(); /* Must read state first. */
  51                         atomic_inc(&stopmachine_thread_ack);
  52                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  53                            && !prepared) {
  54                         /* Everyone is in place, hold CPU. */
  55                         preempt_disable();
  56                         prepared = 1;
  57                         smp_mb(); /* Must read state first. */
  58                         atomic_inc(&stopmachine_thread_ack);
  59                 }
  60                 /* Yield in first stage: migration threads need to
  61                  * help our sisters onto their CPUs. */
  62                 if (!prepared && !irqs_disabled)
  63                         yield();
  64                 else
  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         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
  94
  95         /* One high-prio thread per cpu.  We'll do this one. */
  96         sched_setscheduler(current, SCHED_FIFO, &param);
  97
  98         atomic_set(&stopmachine_thread_ack, 0);
  99         stopmachine_num_threads = 0;
 100         stopmachine_state = STOPMACHINE_WAIT;
 101
 102         for_each_online_cpu(i) {
 103                 if (i == raw_smp_processor_id())
 104                         continue;
 105                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 106                 if (ret < 0)
 107                         break;
 108                 stopmachine_num_threads++;
 109         }
 110
 111         /* Wait for them all to come to life. */
 112         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 113                 yield();
 114
 115         /* If some failed, kill them all. */
 116         if (ret < 0) {
 117                 stopmachine_set_state(STOPMACHINE_EXIT);
 118                 return ret;
 119         }
 120
 121         /* Now they are all started, make them hold the CPUs, ready. */
 122         preempt_disable();
 123         stopmachine_set_state(STOPMACHINE_PREPARE);
 124
 125         /* Make them disable irqs. */
 126         local_irq_disable();
 127         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 128
 129         return 0;
 130 }
 131
 132 static void restart_machine(void)
 133 {
 134         stopmachine_set_state(STOPMACHINE_EXIT);
 135         local_irq_enable();
 136         preempt_enable_no_resched();
 137 }
 138
 139 struct stop_machine_data
 140 {
 141         int (*fn)(void *);
 142         void *data;
 143         struct completion done;
 144 };
 145
 146 static int do_stop(void *_smdata)
 147 {
 148         struct stop_machine_data *smdata = _smdata;
 149         int ret;
 150
 151         ret = stop_machine();
 152         if (ret == 0) {
 153                 ret = smdata->fn(smdata->data);
 154                 restart_machine();
 155         }
 156
 157         /* We're done: you can kthread_stop us now */
 158         complete(&smdata->done);
 159
 160         /* Wait for kthread_stop */
 161         set_current_state(TASK_INTERRUPTIBLE);
 162         while (!kthread_should_stop()) {
 163                 schedule();
 164                 set_current_state(TASK_INTERRUPTIBLE);
 165         }
 166         __set_current_state(TASK_RUNNING);
 167         return ret;
 168 }
 169
 170 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 171                                        unsigned int cpu)
 172 {
 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         down(&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                 kthread_bind(p, cpu);
 189                 wake_up_process(p);
 190                 wait_for_completion(&smdata.done);
 191         }
 192         up(&stopmachine_mutex);
 193         return p;
 194 }
 195
 196 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 197 {
 198         struct task_struct *p;
 199         int ret;
 200
 201         /* No CPUs can come up or down during this. */
 202         lock_cpu_hotplug();
 203         p = __stop_machine_run(fn, data, cpu);
 204         if (!IS_ERR(p))
 205                 ret = kthread_stop(p);
 206         else
 207                 ret = PTR_ERR(p);
 208         unlock_cpu_hotplug();
 209
 210         return ret;
 211 }
 212 EXPORT_SYMBOL_GPL(stop_machine_run);