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         mm_segment_t old_fs = get_fs();
  91
  92         /* One high-prio thread per cpu.  We'll do this one. */
  93         set_fs(KERNEL_DS);
  94         sys_sched_setscheduler(current->pid, SCHED_FIFO,
  95                                 (struct sched_param __user *)&param);
  96         set_fs(old_fs);
  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 == _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                 up(&stopmachine_mutex);
 119                 return ret;
 120         }
 121
 122         /* Don't schedule us away at this point, please. */
 123         local_irq_disable();
 124
 125         /* Now they are all started, make them hold the CPUs, ready. */
 126         stopmachine_set_state(STOPMACHINE_PREPARE);
 127
 128         /* Make them disable irqs. */
 129         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 130
 131         return 0;
 132 }
 133
 134 static void restart_machine(void)
 135 {
 136         stopmachine_set_state(STOPMACHINE_EXIT);
 137         local_irq_enable();
 138 }
 139
 140 struct stop_machine_data
 141 {
 142         int (*fn)(void *);
 143         void *data;
 144         struct completion done;
 145 };
 146
 147 static int do_stop(void *_smdata)
 148 {
 149         struct stop_machine_data *smdata = _smdata;
 150         int ret;
 151
 152         ret = stop_machine();
 153         if (ret == 0) {
 154                 ret = smdata->fn(smdata->data);
 155                 restart_machine();
 156         }
 157
 158         /* We're done: you can kthread_stop us now */
 159         complete(&smdata->done);
 160
 161         /* Wait for kthread_stop */
 162         set_current_state(TASK_INTERRUPTIBLE);
 163         while (!kthread_should_stop()) {
 164                 schedule();
 165                 set_current_state(TASK_INTERRUPTIBLE);
 166         }
 167         __set_current_state(TASK_RUNNING);
 168         return ret;
 169 }
 170
 171 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 172                                        unsigned int cpu)
 173 {
 174         struct stop_machine_data smdata;
 175         struct task_struct *p;
 176
 177         smdata.fn = fn;
 178         smdata.data = data;
 179         init_completion(&smdata.done);
 180
 181         down(&stopmachine_mutex);
 182
 183         /* If they don't care which CPU fn runs on, bind to any online one. */
 184         if (cpu == NR_CPUS)
 185                 cpu = _smp_processor_id();
 186
 187         p = kthread_create(do_stop, &smdata, "kstopmachine");
 188         if (!IS_ERR(p)) {
 189                 kthread_bind(p, cpu);
 190                 wake_up_process(p);
 191                 wait_for_completion(&smdata.done);
 192         }
 193         up(&stopmachine_mutex);
 194         return p;
 195 }
 196
 197 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 198 {
 199         struct task_struct *p;
 200         int ret;
 201
 202         /* No CPUs can come up or down during this. */
 203         lock_cpu_hotplug();
 204         p = __stop_machine_run(fn, data, cpu);
 205         if (!IS_ERR(p))
 206                 ret = kthread_stop(p);
 207         else
 208                 ret = PTR_ERR(p);
 209         unlock_cpu_hotplug();
 210
 211         return ret;
 212 }