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_ptr(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 cpu_relax(); 66 } 67 68 /* Ack: we are exiting. */ 69 smp_mb(); /* Must read state first. */ 70 atomic_inc(&stopmachine_thread_ack); 71 72 if (irqs_disabled) 73 local_irq_enable(); 74 if (prepared) 75 preempt_enable(); 76 77 return 0; 78 } 79 80 /* Change the thread state */ 81 static void stopmachine_set_state(enum stopmachine_state state) 82 { 83 atomic_set(&stopmachine_thread_ack, 0); 84 smp_wmb(); 85 stopmachine_state = state; 86 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) 87 cpu_relax(); 88 } 89 90 static int stop_machine(void) 91 { 92 int i, ret = 0; 93 94 atomic_set(&stopmachine_thread_ack, 0); 95 stopmachine_num_threads = 0; 96 stopmachine_state = STOPMACHINE_WAIT; 97 98 for_each_online_cpu(i) { 99 if (i == raw_smp_processor_id()) 100 continue; 101 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL); 102 if (ret < 0) 103 break; 104 stopmachine_num_threads++; 105 } 106 107 /* Wait for them all to come to life. */ 108 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) { 109 yield(); 110 cpu_relax(); 111 } 112 113 /* If some failed, kill them all. */ 114 if (ret < 0) { 115 stopmachine_set_state(STOPMACHINE_EXIT); 116 return ret; 117 } 118 119 /* Now they are all started, make them hold the CPUs, ready. */ 120 preempt_disable(); 121 stopmachine_set_state(STOPMACHINE_PREPARE); 122 123 /* Make them disable irqs. */ 124 local_irq_disable(); 125 hard_irq_disable(); 126 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ); 127 128 return 0; 129 } 130 131 static void restart_machine(void) 132 { 133 stopmachine_set_state(STOPMACHINE_EXIT); 134 local_irq_enable(); 135 preempt_enable_no_resched(); 136 } 137 138 struct stop_machine_data { 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, ¶m); 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); 216