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/semaphore.h> 15 #include <asm/uaccess.h> 16 17 /* Since we effect priority and affinity (both of which are visible 18 * to, and settable by outside processes) we do indirection via a 19 * kthread. */ 20 21 /* Thread to stop each CPU in user context. */ 22 enum stopmachine_state { 23 STOPMACHINE_WAIT, 24 STOPMACHINE_PREPARE, 25 STOPMACHINE_DISABLE_IRQ, 26 STOPMACHINE_EXIT, 27 }; 28 29 static enum stopmachine_state stopmachine_state; 30 static unsigned int stopmachine_num_threads; 31 static atomic_t stopmachine_thread_ack; 32 33 static int stopmachine(void *cpu) 34 { 35 int irqs_disabled = 0; 36 int prepared = 0; 37 38 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu)); 39 40 /* Ack: we are alive */ 41 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */ 42 atomic_inc(&stopmachine_thread_ack); 43 44 /* Simple state machine */ 45 while (stopmachine_state != STOPMACHINE_EXIT) { 46 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 47 && !irqs_disabled) { 48 local_irq_disable(); 49 hard_irq_disable(); 50 irqs_disabled = 1; 51 /* Ack: irqs disabled. */ 52 smp_mb(); /* Must read state first. */ 53 atomic_inc(&stopmachine_thread_ack); 54 } else if (stopmachine_state == STOPMACHINE_PREPARE 55 && !prepared) { 56 /* Everyone is in place, hold CPU. */ 57 preempt_disable(); 58 prepared = 1; 59 smp_mb(); /* Must read state first. */ 60 atomic_inc(&stopmachine_thread_ack); 61 } 62 /* Yield in first stage: migration threads need to 63 * help our sisters onto their CPUs. */ 64 if (!prepared && !irqs_disabled) 65 yield(); 66 else 67 cpu_relax(); 68 } 69 70 /* Ack: we are exiting. */ 71 smp_mb(); /* Must read state first. */ 72 atomic_inc(&stopmachine_thread_ack); 73 74 if (irqs_disabled) 75 local_irq_enable(); 76 if (prepared) 77 preempt_enable(); 78 79 return 0; 80 } 81 82 /* Change the thread state */ 83 static void stopmachine_set_state(enum stopmachine_state state) 84 { 85 atomic_set(&stopmachine_thread_ack, 0); 86 smp_wmb(); 87 stopmachine_state = state; 88 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) 89 cpu_relax(); 90 } 91 92 static int stop_machine(void) 93 { 94 int i, ret = 0; 95 96 atomic_set(&stopmachine_thread_ack, 0); 97 stopmachine_num_threads = 0; 98 stopmachine_state = STOPMACHINE_WAIT; 99 100 for_each_online_cpu(i) { 101 if (i == raw_smp_processor_id()) 102 continue; 103 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL); 104 if (ret < 0) 105 break; 106 stopmachine_num_threads++; 107 } 108 109 /* Wait for them all to come to life. */ 110 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) 111 yield(); 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 { 140 int (*fn)(void *); 141 void *data; 142 struct completion done; 143 }; 144 145 static int do_stop(void *_smdata) 146 { 147 struct stop_machine_data *smdata = _smdata; 148 int ret; 149 150 ret = stop_machine(); 151 if (ret == 0) { 152 ret = smdata->fn(smdata->data); 153 restart_machine(); 154 } 155 156 /* We're done: you can kthread_stop us now */ 157 complete(&smdata->done); 158 159 /* Wait for kthread_stop */ 160 set_current_state(TASK_INTERRUPTIBLE); 161 while (!kthread_should_stop()) { 162 schedule(); 163 set_current_state(TASK_INTERRUPTIBLE); 164 } 165 __set_current_state(TASK_RUNNING); 166 return ret; 167 } 168 169 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data, 170 unsigned int cpu) 171 { 172 static DEFINE_MUTEX(stopmachine_mutex); 173 struct stop_machine_data smdata; 174 struct task_struct *p; 175 176 smdata.fn = fn; 177 smdata.data = data; 178 init_completion(&smdata.done); 179 180 mutex_lock(&stopmachine_mutex); 181 182 /* If they don't care which CPU fn runs on, bind to any online one. */ 183 if (cpu == NR_CPUS) 184 cpu = raw_smp_processor_id(); 185 186 p = kthread_create(do_stop, &smdata, "kstopmachine"); 187 if (!IS_ERR(p)) { 188 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 }; 189 190 /* One high-prio thread per cpu. We'll do this one. */ 191 sched_setscheduler(p, SCHED_FIFO, ¶m); 192 kthread_bind(p, cpu); 193 wake_up_process(p); 194 wait_for_completion(&smdata.done); 195 } 196 mutex_unlock(&stopmachine_mutex); 197 return p; 198 } 199 200 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu) 201 { 202 struct task_struct *p; 203 int ret; 204 205 /* No CPUs can come up or down during this. */ 206 get_online_cpus(); 207 p = __stop_machine_run(fn, data, cpu); 208 if (!IS_ERR(p)) 209 ret = kthread_stop(p); 210 else 211 ret = PTR_ERR(p); 212 put_online_cpus(); 213 214 return ret; 215 } 216 EXPORT_SYMBOL_GPL(stop_machine_run); 217