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                 cpu_relax();
  56         }
  57
  58         /* Ack: we are exiting. */
  59         mb(); /* Must read state first. */
  60         atomic_inc(&stopmachine_thread_ack);
  61
  62         if (irqs_disabled)
  63                 local_irq_enable();
  64         if (prepared)
  65                 preempt_enable();
  66
  67         return 0;
  68 }
  69
  70 /* Change the thread state */
  71 static void stopmachine_set_state(enum stopmachine_state state)
  72 {
  73         atomic_set(&stopmachine_thread_ack, 0);
  74         wmb();
  75         stopmachine_state = state;
  76         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  77                 cpu_relax();
  78 }
  79
  80 static int stop_machine(void)
  81 {
  82         int i, ret = 0;
  83         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
  84
  85         /* One high-prio thread per cpu.  We'll do this one. */
  86         sys_sched_setscheduler(current->pid, SCHED_FIFO, &param);
  87
  88         atomic_set(&stopmachine_thread_ack, 0);
  89         stopmachine_num_threads = 0;
  90         stopmachine_state = STOPMACHINE_WAIT;
  91
  92         for_each_online_cpu(i) {
  93                 if (i == smp_processor_id())
  94                         continue;
  95                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
  96                 if (ret < 0)
  97                         break;
  98                 stopmachine_num_threads++;
  99         }
 100
 101         /* Wait for them all to come to life. */
 102         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 103                 yield();
 104
 105         /* If some failed, kill them all. */
 106         if (ret < 0) {
 107                 stopmachine_set_state(STOPMACHINE_EXIT);
 108                 up(&stopmachine_mutex);
 109                 return ret;
 110         }
 111
 112         /* Don't schedule us away at this point, please. */
 113         local_irq_disable();
 114
 115         /* Now they are all started, make them hold the CPUs, ready. */
 116         stopmachine_set_state(STOPMACHINE_PREPARE);
 117
 118         /* Make them disable irqs. */
 119         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 120
 121         return 0;
 122 }
 123
 124 static void restart_machine(void)
 125 {
 126         stopmachine_set_state(STOPMACHINE_EXIT);
 127         local_irq_enable();
 128 }
 129
 130 struct stop_machine_data
 131 {
 132         int (*fn)(void *);
 133         void *data;
 134         struct completion done;
 135 };
 136
 137 static int do_stop(void *_smdata)
 138 {
 139         struct stop_machine_data *smdata = _smdata;
 140         int ret;
 141
 142         ret = stop_machine();
 143         if (ret == 0) {
 144                 ret = smdata->fn(smdata->data);
 145                 restart_machine();
 146         }
 147
 148         /* We're done: you can kthread_stop us now */
 149         complete(&smdata->done);
 150
 151         /* Wait for kthread_stop */
 152         set_current_state(TASK_INTERRUPTIBLE);
 153         while (!kthread_should_stop()) {
 154                 schedule();
 155                 set_current_state(TASK_INTERRUPTIBLE);
 156         }
 157         __set_current_state(TASK_RUNNING);
 158         return ret;
 159 }
 160
 161 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 162                                        unsigned int cpu)
 163 {
 164         struct stop_machine_data smdata;
 165         struct task_struct *p;
 166
 167         smdata.fn = fn;
 168         smdata.data = data;
 169         init_completion(&smdata.done);
 170
 171         down(&stopmachine_mutex);
 172
 173         /* If they don't care which CPU fn runs on, bind to any online one. */
 174         if (cpu == NR_CPUS)
 175                 cpu = smp_processor_id();
 176
 177         p = kthread_create(do_stop, &smdata, "kstopmachine");
 178         if (!IS_ERR(p)) {
 179                 kthread_bind(p, cpu);
 180                 wake_up_process(p);
 181                 wait_for_completion(&smdata.done);
 182         }
 183         up(&stopmachine_mutex);
 184         return p;
 185 }
 186
 187 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 188 {
 189         struct task_struct *p;
 190         int ret;
 191
 192         /* No CPUs can come up or down during this. */
 193         lock_cpu_hotplug();
 194         p = __stop_machine_run(fn, data, cpu);
 195         if (!IS_ERR(p))
 196                 ret = kthread_stop(p);
 197         else
 198                 ret = PTR_ERR(p);
 199         unlock_cpu_hotplug();
 200
 201         return ret;
 202 }