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/uaccess.h>
  15
  16 /* Since we effect priority and affinity (both of which are visible
  17  * to, and settable by outside processes) we do indirection via a
  18  * kthread. */
  19
  20 /* Thread to stop each CPU in user context. */
  21 enum stopmachine_state {
  22         STOPMACHINE_WAIT,
  23         STOPMACHINE_PREPARE,
  24         STOPMACHINE_DISABLE_IRQ,
  25         STOPMACHINE_EXIT,
  26 };
  27
  28 static enum stopmachine_state stopmachine_state;
  29 static unsigned int stopmachine_num_threads;
  30 static atomic_t stopmachine_thread_ack;
  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                         hard_irq_disable();
  49                         irqs_disabled = 1;
  50                         /* Ack: irqs disabled. */
  51                         smp_mb(); /* Must read state first. */
  52                         atomic_inc(&stopmachine_thread_ack);
  53                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  54                            && !prepared) {
  55                         /* Everyone is in place, hold CPU. */
  56                         preempt_disable();
  57                         prepared = 1;
  58                         smp_mb(); /* Must read state first. */
  59                         atomic_inc(&stopmachine_thread_ack);
  60                 }
  61                 /* Yield in first stage: migration threads need to
  62                  * help our sisters onto their CPUs. */
  63                 if (!prepared && !irqs_disabled)
  64                         yield();
  65                 else
  66                         cpu_relax();
  67         }
  68
  69         /* Ack: we are exiting. */
  70         smp_mb(); /* Must read state first. */
  71         atomic_inc(&stopmachine_thread_ack);
  72
  73         if (irqs_disabled)
  74                 local_irq_enable();
  75         if (prepared)
  76                 preempt_enable();
  77
  78         return 0;
  79 }
  80
  81 /* Change the thread state */
  82 static void stopmachine_set_state(enum stopmachine_state state)
  83 {
  84         atomic_set(&stopmachine_thread_ack, 0);
  85         smp_wmb();
  86         stopmachine_state = state;
  87         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
  88                 cpu_relax();
  89 }
  90
  91 static int stop_machine(void)
  92 {
  93         int i, ret = 0;
  94
  95         atomic_set(&stopmachine_thread_ack, 0);
  96         stopmachine_num_threads = 0;
  97         stopmachine_state = STOPMACHINE_WAIT;
  98
  99         for_each_online_cpu(i) {
 100                 if (i == raw_smp_processor_id())
 101                         continue;
 102                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 103                 if (ret < 0)
 104                         break;
 105                 stopmachine_num_threads++;
 106         }
 107
 108         /* Wait for them all to come to life. */
 109         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 110                 yield();
 111
 112         /* If some failed, kill them all. */
 113         if (ret < 0) {
 114                 stopmachine_set_state(STOPMACHINE_EXIT);
 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         hard_irq_disable();
 125         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 126
 127         return 0;
 128 }
 129
 130 static void restart_machine(void)
 131 {
 132         stopmachine_set_state(STOPMACHINE_EXIT);
 133         local_irq_enable();
 134         preempt_enable_no_resched();
 135 }
 136
 137 struct stop_machine_data
 138 {
 139         int (*fn)(void *);
 140         void *data;
 141         struct completion done;
 142 };
 143
 144 static int do_stop(void *_smdata)
 145 {
 146         struct stop_machine_data *smdata = _smdata;
 147         int ret;
 148
 149         ret = stop_machine();
 150         if (ret == 0) {
 151                 ret = smdata->fn(smdata->data);
 152                 restart_machine();
 153         }
 154
 155         /* We're done: you can kthread_stop us now */
 156         complete(&smdata->done);
 157
 158         /* Wait for kthread_stop */
 159         set_current_state(TASK_INTERRUPTIBLE);
 160         while (!kthread_should_stop()) {
 161                 schedule();
 162                 set_current_state(TASK_INTERRUPTIBLE);
 163         }
 164         __set_current_state(TASK_RUNNING);
 165         return ret;
 166 }
 167
 168 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 169                                        unsigned int cpu)
 170 {
 171         static DEFINE_MUTEX(stopmachine_mutex);
 172         struct stop_machine_data smdata;
 173         struct task_struct *p;
 174
 175         smdata.fn = fn;
 176         smdata.data = data;
 177         init_completion(&smdata.done);
 178
 179         mutex_lock(&stopmachine_mutex);
 180
 181         /* If they don't care which CPU fn runs on, bind to any online one. */
 182         if (cpu == NR_CPUS)
 183                 cpu = raw_smp_processor_id();
 184
 185         p = kthread_create(do_stop, &smdata, "kstopmachine");
 186         if (!IS_ERR(p)) {
 187                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 188
 189                 /* One high-prio thread per cpu.  We'll do this one. */
 190                 sched_setscheduler(p, SCHED_FIFO, &param);
 191                 kthread_bind(p, cpu);
 192                 wake_up_process(p);
 193                 wait_for_completion(&smdata.done);
 194         }
 195         mutex_unlock(&stopmachine_mutex);
 196         return p;
 197 }
 198
 199 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 200 {
 201         struct task_struct *p;
 202         int ret;
 203
 204         /* No CPUs can come up or down during this. */
 205         get_online_cpus();
 206         p = __stop_machine_run(fn, data, cpu);
 207         if (!IS_ERR(p))
 208                 ret = kthread_stop(p);
 209         else
 210                 ret = PTR_ERR(p);
 211         put_online_cpus();
 212
 213         return ret;
 214 }
 215 EXPORT_SYMBOL_GPL(stop_machine_run);