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
  10 /* Since we effect priority and affinity (both of which are visible
  11  * to, and settable by outside processes) we do indirection via a
  12  * kthread. */
  13
  14 /* Thread to stop each CPU in user context. */
  15 enum stopmachine_state {
  16         STOPMACHINE_WAIT,
  17         STOPMACHINE_PREPARE,
  18         STOPMACHINE_DISABLE_IRQ,
  19         STOPMACHINE_EXIT,
  20 };
  21
  22 static enum stopmachine_state stopmachine_state;
  23 static unsigned int stopmachine_num_threads;
  24 static atomic_t stopmachine_thread_ack;
  25 static DECLARE_MUTEX(stopmachine_mutex);
  26
  27 static int stopmachine(void *cpu)
  28 {
  29         int irqs_disabled = 0;
  30         int prepared = 0;
  31
  32         set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
  33
  34         /* Ack: we are alive */
  35         mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
  36         atomic_inc(&stopmachine_thread_ack);
  37
  38         /* Simple state machine */
  39         while (stopmachine_state != STOPMACHINE_EXIT) {
  40                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
  41                     && !irqs_disabled) {
  42                         local_irq_disable();
  43                         irqs_disabled = 1;
  44                         /* Ack: irqs disabled. */
  45                         mb(); /* Must read state first. */
  46                         atomic_inc(&stopmachine_thread_ack);
  47                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  48                            && !prepared) {
  49                         /* Everyone is in place, hold CPU. */
  50                         preempt_disable();
  51                         prepared = 1;
  52                         mb(); /* Must read state first. */
  53                         atomic_inc(&stopmachine_thread_ack);
  54                 }
  55                 /* Yield in first stage: migration threads need to
  56                  * help our sisters onto their CPUs. */
  57                 if (!prepared && !irqs_disabled)
  58                         yield();
  59                 else
  60                         cpu_relax();
  61         }
  62
  63         /* Ack: we are exiting. */
  64         mb(); /* Must read state first. */
  65         atomic_inc(&stopmachine_thread_ack);
  66
  67         if (irqs_disabled)
  68                 local_irq_enable();
  69         if (prepared)
  70                 preempt_enable();
  71
  72         return 0;
  73 }
  74
  75 /* Change the thread state */
  76 static void stopmachine_set_state(enum stopmachine_state state)
  77 {
  78         atomic_set(&stopmachine_thread_ack, 0);
  79         wmb();
  80         stopmachine_state = state;
  81         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  82                 cpu_relax();
  83 }
  84
  85 static int stop_machine(void)
  86 {
  87         int i, ret = 0;
  88         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
  89
  90         /* One high-prio thread per cpu.  We'll do this one. */
  91         sys_sched_setscheduler(current->pid, SCHED_FIFO, &param);
  92
  93         atomic_set(&stopmachine_thread_ack, 0);
  94         stopmachine_num_threads = 0;
  95         stopmachine_state = STOPMACHINE_WAIT;
  96
  97         for_each_online_cpu(i) {
  98                 if (i == _smp_processor_id())
  99                         continue;
 100                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 101                 if (ret < 0)
 102                         break;
 103                 stopmachine_num_threads++;
 104         }
 105
 106         /* Wait for them all to come to life. */
 107         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 108                 yield();
 109
 110         /* If some failed, kill them all. */
 111         if (ret < 0) {
 112                 stopmachine_set_state(STOPMACHINE_EXIT);
 113                 up(&stopmachine_mutex);
 114                 return ret;
 115         }
 116
 117         /* Don't schedule us away at this point, please. */
 118         local_irq_disable();
 119
 120         /* Now they are all started, make them hold the CPUs, ready. */
 121         stopmachine_set_state(STOPMACHINE_PREPARE);
 122
 123         /* Make them disable irqs. */
 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 }
 134
 135 struct stop_machine_data
 136 {
 137         int (*fn)(void *);
 138         void *data;
 139         struct completion done;
 140 };
 141
 142 static int do_stop(void *_smdata)
 143 {
 144         struct stop_machine_data *smdata = _smdata;
 145         int ret;
 146
 147         ret = stop_machine();
 148         if (ret == 0) {
 149                 ret = smdata->fn(smdata->data);
 150                 restart_machine();
 151         }
 152
 153         /* We're done: you can kthread_stop us now */
 154         complete(&smdata->done);
 155
 156         /* Wait for kthread_stop */
 157         set_current_state(TASK_INTERRUPTIBLE);
 158         while (!kthread_should_stop()) {
 159                 schedule();
 160                 set_current_state(TASK_INTERRUPTIBLE);
 161         }
 162         __set_current_state(TASK_RUNNING);
 163         return ret;
 164 }
 165
 166 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 167                                        unsigned int cpu)
 168 {
 169         struct stop_machine_data smdata;
 170         struct task_struct *p;
 171
 172         smdata.fn = fn;
 173         smdata.data = data;
 174         init_completion(&smdata.done);
 175
 176         down(&stopmachine_mutex);
 177
 178         /* If they don't care which CPU fn runs on, bind to any online one. */
 179         if (cpu == NR_CPUS)
 180                 cpu = _smp_processor_id();
 181
 182         p = kthread_create(do_stop, &smdata, "kstopmachine");
 183         if (!IS_ERR(p)) {
 184                 kthread_bind(p, cpu);
 185                 wake_up_process(p);
 186                 wait_for_completion(&smdata.done);
 187         }
 188         up(&stopmachine_mutex);
 189         return p;
 190 }
 191
 192 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 193 {
 194         struct task_struct *p;
 195         int ret;
 196
 197         /* No CPUs can come up or down during this. */
 198         lock_cpu_hotplug();
 199         p = __stop_machine_run(fn, data, cpu);
 200         if (!IS_ERR(p))
 201                 ret = kthread_stop(p);
 202         else
 203                 ret = PTR_ERR(p);
 204         unlock_cpu_hotplug();
 205
 206         return ret;
 207 }