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 91 /* One high-prio thread per cpu. We'll do this one. */ 92 sched_setscheduler(current, SCHED_FIFO, ¶m); 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(); 110 111 /* If some failed, kill them all. */ 112 if (ret < 0) { 113 stopmachine_set_state(STOPMACHINE_EXIT); 114 return ret; 115 } 116 117 /* Now they are all started, make them hold the CPUs, ready. */ 118 preempt_disable(); 119 stopmachine_set_state(STOPMACHINE_PREPARE); 120 121 /* Make them disable irqs. */ 122 local_irq_disable(); 123 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ); 124 125 return 0; 126 } 127 128 static void restart_machine(void) 129 { 130 stopmachine_set_state(STOPMACHINE_EXIT); 131 local_irq_enable(); 132 preempt_enable_no_resched(); 133 } 134 135 struct stop_machine_data 136 { 137 int (*fn)(void *); 138 void *data; 139 struct completion done; 140 }; 141 142 static int do_stop(void *_smdata) 143 { 144 struct stop_machine_data *smdata = _smdata; 145 int ret; 146 147 ret = stop_machine(); 148 if (ret == 0) { 149 ret = smdata->fn(smdata->data); 150 restart_machine(); 151 } 152 153 /* We're done: you can kthread_stop us now */ 154 complete(&smdata->done); 155 156 /* Wait for kthread_stop */ 157 set_current_state(TASK_INTERRUPTIBLE); 158 while (!kthread_should_stop()) { 159 schedule(); 160 set_current_state(TASK_INTERRUPTIBLE); 161 } 162 __set_current_state(TASK_RUNNING); 163 return ret; 164 } 165 166 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data, 167 unsigned int cpu) 168 { 169 struct stop_machine_data smdata; 170 struct task_struct *p; 171 172 smdata.fn = fn; 173 smdata.data = data; 174 init_completion(&smdata.done); 175 176 down(&stopmachine_mutex); 177 178 /* If they don't care which CPU fn runs on, bind to any online one. */ 179 if (cpu == NR_CPUS) 180 cpu = raw_smp_processor_id(); 181 182 p = kthread_create(do_stop, &smdata, "kstopmachine"); 183 if (!IS_ERR(p)) { 184 kthread_bind(p, cpu); 185 wake_up_process(p); 186 wait_for_completion(&smdata.done); 187 } 188 up(&stopmachine_mutex); 189 return p; 190 } 191 192 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu) 193 { 194 struct task_struct *p; 195 int ret; 196 197 /* No CPUs can come up or down during this. */ 198 lock_cpu_hotplug(); 199 p = __stop_machine_run(fn, data, cpu); 200 if (!IS_ERR(p)) 201 ret = kthread_stop(p); 202 else 203 ret = PTR_ERR(p); 204 unlock_cpu_hotplug(); 205 206 return ret; 207 } 208