kernel/stop_machine.c

   1 #include <linux/stop_machine.h>
   2 #include <linux/kthread.h>
   3 #include <linux/sched.h>
   4 #include <linux/cpu.h>
   5 #include <linux/err.h>
   6 #include <linux/syscalls.h>
   7 #include <asm/atomic.h>
   8 #include <asm/semaphore.h>
   9 #include <asm/uaccess.h>
  10
  11 /* Since we effect priority and affinity (both of which are visible
  12  * to, and settable by outside processes) we do indirection via a
  13  * kthread. */
  14
  15 /* Thread to stop each CPU in user context. */
  16 enum stopmachine_state {
  17         STOPMACHINE_WAIT,
  18         STOPMACHINE_PREPARE,
  19         STOPMACHINE_DISABLE_IRQ,
  20         STOPMACHINE_EXIT,
  21 };
  22
  23 static enum stopmachine_state stopmachine_state;
  24 static unsigned int stopmachine_num_threads;
  25 static atomic_t stopmachine_thread_ack;
  26 static DECLARE_MUTEX(stopmachine_mutex);
  27
  28 static int stopmachine(void *cpu)
  29 {
  30         int irqs_disabled = 0;
  31         int prepared = 0;
  32
  33         set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
  34
  35         /* Ack: we are alive */
  36         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
  37         atomic_inc(&stopmachine_thread_ack);
  38
  39         /* Simple state machine */
  40         while (stopmachine_state != STOPMACHINE_EXIT) {
  41                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
  42                     && !irqs_disabled) {
  43                         local_irq_disable();
  44                         irqs_disabled = 1;
  45                         /* Ack: irqs disabled. */
  46                         smp_mb(); /* Must read state first. */
  47                         atomic_inc(&stopmachine_thread_ack);
  48                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  49                            && !prepared) {
  50                         /* Everyone is in place, hold CPU. */
  51                         preempt_disable();
  52                         prepared = 1;
  53                         smp_mb(); /* Must read state first. */
  54                         atomic_inc(&stopmachine_thread_ack);
  55                 }
  56                 /* Yield in first stage: migration threads need to
  57                  * help our sisters onto their CPUs. */
  58                 if (!prepared && !irqs_disabled)
  59                         yield();
  60                 else
  61                         cpu_relax();
  62         }
  63
  64         /* Ack: we are exiting. */
  65         smp_mb(); /* Must read state first. */
  66         atomic_inc(&stopmachine_thread_ack);
  67
  68         if (irqs_disabled)
  69                 local_irq_enable();
  70         if (prepared)
  71                 preempt_enable();
  72
  73         return 0;
  74 }
  75
  76 /* Change the thread state */
  77 static void stopmachine_set_state(enum stopmachine_state state)
  78 {
  79         atomic_set(&stopmachine_thread_ack, 0);
  80         smp_wmb();
  81         stopmachine_state = state;
  82         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  83                 cpu_relax();
  84 }
  85
  86 static int stop_machine(void)
  87 {
  88         int i, ret = 0;
  89         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
  90
  91         /* One high-prio thread per cpu.  We'll do this one. */
  92         sched_setscheduler(current, SCHED_FIFO, &param);
  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
 111         /* If some failed, kill them all. */
 112         if (ret < 0) {
 113                 stopmachine_set_state(STOPMACHINE_EXIT);
 114                 up(&stopmachine_mutex);
 115                 return ret;
 116         }
 117
 118         /* Now they are all started, make them hold the CPUs, ready. */
 119         preempt_disable();
 120         stopmachine_set_state(STOPMACHINE_PREPARE);
 121
 122         /* Make them disable irqs. */
 123         local_irq_disable();
 124         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 125
 126         return 0;
 127 }
 128
 129 static void restart_machine(void)
 130 {
 131         stopmachine_set_state(STOPMACHINE_EXIT);
 132         local_irq_enable();
 133         preempt_enable_no_resched();
 134 }
 135
 136 struct stop_machine_data
 137 {
 138         int (*fn)(void *);
 139         void *data;
 140         struct completion done;
 141 };
 142
 143 static int do_stop(void *_smdata)
 144 {
 145         struct stop_machine_data *smdata = _smdata;
 146         int ret;
 147
 148         ret = stop_machine();
 149         if (ret == 0) {
 150                 ret = smdata->fn(smdata->data);
 151                 restart_machine();
 152         }
 153
 154         /* We're done: you can kthread_stop us now */
 155         complete(&smdata->done);
 156
 157         /* Wait for kthread_stop */
 158         set_current_state(TASK_INTERRUPTIBLE);
 159         while (!kthread_should_stop()) {
 160                 schedule();
 161                 set_current_state(TASK_INTERRUPTIBLE);
 162         }
 163         __set_current_state(TASK_RUNNING);
 164         return ret;
 165 }
 166
 167 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 168                                        unsigned int cpu)
 169 {
 170         struct stop_machine_data smdata;
 171         struct task_struct *p;
 172
 173         smdata.fn = fn;
 174         smdata.data = data;
 175         init_completion(&smdata.done);
 176
 177         down(&stopmachine_mutex);
 178
 179         /* If they don't care which CPU fn runs on, bind to any online one. */
 180         if (cpu == NR_CPUS)
 181                 cpu = raw_smp_processor_id();
 182
 183         p = kthread_create(do_stop, &smdata, "kstopmachine");
 184         if (!IS_ERR(p)) {
 185                 kthread_bind(p, cpu);
 186                 wake_up_process(p);
 187                 wait_for_completion(&smdata.done);
 188         }
 189         up(&stopmachine_mutex);
 190         return p;
 191 }
 192
 193 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 194 {
 195         struct task_struct *p;
 196         int ret;
 197
 198         /* No CPUs can come up or down during this. */
 199         lock_cpu_hotplug();
 200         p = __stop_machine_run(fn, data, cpu);
 201         if (!IS_ERR(p))
 202                 ret = kthread_stop(p);
 203         else
 204                 ret = PTR_ERR(p);
 205         unlock_cpu_hotplug();
 206
 207         return ret;
 208 }