SAFE public projects git trees. - safe/jmp/linux-2.6/blob - 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_RUN,
  26         STOPMACHINE_EXIT,
  27 };
  28
  29 struct stop_machine_data {
  30         int (*fn)(void *);
  31         void *data;
  32         struct completion done;
  33         int run_all;
  34 } smdata;
  35
  36 static enum stopmachine_state stopmachine_state;
  37 static unsigned int stopmachine_num_threads;
  38 static atomic_t stopmachine_thread_ack;
  39
  40 static int stopmachine(void *cpu)
  41 {
  42         int irqs_disabled = 0;
  43         int prepared = 0;
  44         int ran = 0;
  45         cpumask_of_cpu_ptr(cpumask, (int)(long)cpu);
  46
  47         set_cpus_allowed_ptr(current, cpumask);
  48
  49         /* Ack: we are alive */
  50         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
  51         atomic_inc(&stopmachine_thread_ack);
  52
  53         /* Simple state machine */
  54         while (stopmachine_state != STOPMACHINE_EXIT) {
  55                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
  56                     && !irqs_disabled) {
  57                         local_irq_disable();
  58                         hard_irq_disable();
  59                         irqs_disabled = 1;
  60                         /* Ack: irqs disabled. */
  61                         smp_mb(); /* Must read state first. */
  62                         atomic_inc(&stopmachine_thread_ack);
  63                 } else if (stopmachine_state == STOPMACHINE_PREPARE
  64                            && !prepared) {
  65                         /* Everyone is in place, hold CPU. */
  66                         preempt_disable();
  67                         prepared = 1;
  68                         smp_mb(); /* Must read state first. */
  69                         atomic_inc(&stopmachine_thread_ack);
  70                 } else if (stopmachine_state == STOPMACHINE_RUN && !ran) {
  71                         smdata.fn(smdata.data);
  72                         ran = 1;
  73                         smp_mb(); /* Must read state first. */
  74                         atomic_inc(&stopmachine_thread_ack);
  75                 }
  76                 /* Yield in first stage: migration threads need to
  77                  * help our sisters onto their CPUs. */
  78                 if (!prepared && !irqs_disabled)
  79                         yield();
  80                 cpu_relax();
  81         }
  82
  83         /* Ack: we are exiting. */
  84         smp_mb(); /* Must read state first. */
  85         atomic_inc(&stopmachine_thread_ack);
  86
  87         if (irqs_disabled)
  88                 local_irq_enable();
  89         if (prepared)
  90                 preempt_enable();
  91
  92         return 0;
  93 }
  94
  95 /* Change the thread state */
  96 static void stopmachine_set_state(enum stopmachine_state state)
  97 {
  98         atomic_set(&stopmachine_thread_ack, 0);
  99         smp_wmb();
 100         stopmachine_state = state;
 101         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 102                 cpu_relax();
 103 }
 104
 105 static int stop_machine(void)
 106 {
 107         int i, ret = 0;
 108
 109         atomic_set(&stopmachine_thread_ack, 0);
 110         stopmachine_num_threads = 0;
 111         stopmachine_state = STOPMACHINE_WAIT;
 112
 113         for_each_online_cpu(i) {
 114                 if (i == raw_smp_processor_id())
 115                         continue;
 116                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
 117                 if (ret < 0)
 118                         break;
 119                 stopmachine_num_threads++;
 120         }
 121
 122         /* Wait for them all to come to life. */
 123         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) {
 124                 yield();
 125                 cpu_relax();
 126         }
 127
 128         /* If some failed, kill them all. */
 129         if (ret < 0) {
 130                 stopmachine_set_state(STOPMACHINE_EXIT);
 131                 return ret;
 132         }
 133
 134         /* Now they are all started, make them hold the CPUs, ready. */
 135         preempt_disable();
 136         stopmachine_set_state(STOPMACHINE_PREPARE);
 137
 138         /* Make them disable irqs. */
 139         local_irq_disable();
 140         hard_irq_disable();
 141         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 142
 143         return 0;
 144 }
 145
 146 static void restart_machine(void)
 147 {
 148         stopmachine_set_state(STOPMACHINE_EXIT);
 149         local_irq_enable();
 150         preempt_enable_no_resched();
 151 }
 152
 153 static void run_other_cpus(void)
 154 {
 155         stopmachine_set_state(STOPMACHINE_RUN);
 156 }
 157
 158 static int do_stop(void *_smdata)
 159 {
 160         struct stop_machine_data *smdata = _smdata;
 161         int ret;
 162
 163         ret = stop_machine();
 164         if (ret == 0) {
 165                 ret = smdata->fn(smdata->data);
 166                 if (smdata->run_all)
 167                         run_other_cpus();
 168                 restart_machine();
 169         }
 170
 171         /* We're done: you can kthread_stop us now */
 172         complete(&smdata->done);
 173
 174         /* Wait for kthread_stop */
 175         set_current_state(TASK_INTERRUPTIBLE);
 176         while (!kthread_should_stop()) {
 177                 schedule();
 178                 set_current_state(TASK_INTERRUPTIBLE);
 179         }
 180         __set_current_state(TASK_RUNNING);
 181         return ret;
 182 }
 183
 184 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 185                                        unsigned int cpu)
 186 {
 187         static DEFINE_MUTEX(stopmachine_mutex);
 188         struct stop_machine_data smdata;
 189         struct task_struct *p;
 190
 191         mutex_lock(&stopmachine_mutex);
 192
 193         smdata.fn = fn;
 194         smdata.data = data;
 195         smdata.run_all = (cpu == ALL_CPUS) ? 1 : 0;
 196         init_completion(&smdata.done);
 197
 198         smp_wmb(); /* make sure other cpus see smdata updates */
 199
 200         /* If they don't care which CPU fn runs on, bind to any online one. */
 201         if (cpu == NR_CPUS || cpu == ALL_CPUS)
 202                 cpu = raw_smp_processor_id();
 203
 204         p = kthread_create(do_stop, &smdata, "kstopmachine");
 205         if (!IS_ERR(p)) {
 206                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 207
 208                 /* One high-prio thread per cpu.  We'll do this one. */
 209                 sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
 210                 kthread_bind(p, cpu);
 211                 wake_up_process(p);
 212                 wait_for_completion(&smdata.done);
 213         }
 214         mutex_unlock(&stopmachine_mutex);
 215         return p;
 216 }
 217
 218 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 219 {
 220         struct task_struct *p;
 221         int ret;
 222
 223         /* No CPUs can come up or down during this. */
 224         get_online_cpus();
 225         p = __stop_machine_run(fn, data, cpu);
 226         if (!IS_ERR(p))
 227                 ret = kthread_stop(p);
 228         else
 229                 ret = PTR_ERR(p);
 230         put_online_cpus();
 231
 232         return ret;
 233 }
 234 EXPORT_SYMBOL_GPL(stop_machine_run);