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 static DECLARE_MUTEX(stopmachine_mutex); 33 34 static int stopmachine(void *cpu) 35 { 36 int irqs_disabled = 0; 37 int prepared = 0; 38 39 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu)); 40 41 /* Ack: we are alive */ 42 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */ 43 atomic_inc(&stopmachine_thread_ack); 44 45 /* Simple state machine */ 46 while (stopmachine_state != STOPMACHINE_EXIT) { 47 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 48 && !irqs_disabled) { 49 local_irq_disable(); 50 hard_irq_disable(); 51 irqs_disabled = 1; 52 /* Ack: irqs disabled. */ 53 smp_mb(); /* Must read state first. */ 54 atomic_inc(&stopmachine_thread_ack); 55 } else if (stopmachine_state == STOPMACHINE_PREPARE 56 && !prepared) { 57 /* Everyone is in place, hold CPU. */ 58 preempt_disable(); 59 prepared = 1; 60 smp_mb(); /* Must read state first. */ 61 atomic_inc(&stopmachine_thread_ack); 62 } 63 /* Yield in first stage: migration threads need to 64 * help our sisters onto their CPUs. */ 65 if (!prepared && !irqs_disabled) 66 yield(); 67 else 68 cpu_relax(); 69 } 70 71 /* Ack: we are exiting. */ 72 smp_mb(); /* Must read state first. */ 73 atomic_inc(&stopmachine_thread_ack); 74 75 if (irqs_disabled) 76 local_irq_enable(); 77 if (prepared) 78 preempt_enable(); 79 80 return 0; 81 } 82 83 /* Change the thread state */ 84 static void stopmachine_set_state(enum stopmachine_state state) 85 { 86 atomic_set(&stopmachine_thread_ack, 0); 87 smp_wmb(); 88 stopmachine_state = state; 89 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) 90 cpu_relax(); 91 } 92 93 static int stop_machine(void) 94 { 95 int i, ret = 0; 96 97 atomic_set(&stopmachine_thread_ack, 0); 98 stopmachine_num_threads = 0; 99 stopmachine_state = STOPMACHINE_WAIT; 100 101 for_each_online_cpu(i) { 102 if (i == raw_smp_processor_id()) 103 continue; 104 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL); 105 if (ret < 0) 106 break; 107 stopmachine_num_threads++; 108 } 109 110 /* Wait for them all to come to life. */ 111 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) 112 yield(); 113 114 /* If some failed, kill them all. */ 115 if (ret < 0) { 116 stopmachine_set_state(STOPMACHINE_EXIT); 117 return ret; 118 } 119 120 /* Now they are all started, make them hold the CPUs, ready. */ 121 preempt_disable(); 122 stopmachine_set_state(STOPMACHINE_PREPARE); 123 124 /* Make them disable irqs. */ 125 local_irq_disable(); 126 hard_irq_disable(); 127 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ); 128 129 return 0; 130 } 131 132 static void restart_machine(void) 133 { 134 stopmachine_set_state(STOPMACHINE_EXIT); 135 local_irq_enable(); 136 preempt_enable_no_resched(); 137 } 138 139 struct stop_machine_data 140 { 141 int (*fn)(void *); 142 void *data; 143 struct completion done; 144 }; 145 146 static int do_stop(void *_smdata) 147 { 148 struct stop_machine_data *smdata = _smdata; 149 int ret; 150 151 ret = stop_machine(); 152 if (ret == 0) { 153 ret = smdata->fn(smdata->data); 154 restart_machine(); 155 } 156 157 /* We're done: you can kthread_stop us now */ 158 complete(&smdata->done); 159 160 /* Wait for kthread_stop */ 161 set_current_state(TASK_INTERRUPTIBLE); 162 while (!kthread_should_stop()) { 163 schedule(); 164 set_current_state(TASK_INTERRUPTIBLE); 165 } 166 __set_current_state(TASK_RUNNING); 167 return ret; 168 } 169 170 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data, 171 unsigned int cpu) 172 { 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 down(&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 up(&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 lock_cpu_hotplug(); 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 unlock_cpu_hotplug(); 213 214 return ret; 215 } 216 EXPORT_SYMBOL_GPL(stop_machine_run); 217