1 #include <linux/stop_machine.h>
2 #include <linux/kthread.h>
3 #include <linux/sched.h>
6 #include <linux/syscalls.h>
7 #include <asm/atomic.h>
8 #include <asm/semaphore.h>
9 #include <asm/uaccess.h>
11 /* Since we effect priority and affinity (both of which are visible
12 * to, and settable by outside processes) we do indirection via a
15 /* Thread to stop each CPU in user context. */
16 enum stopmachine_state {
19 STOPMACHINE_DISABLE_IRQ,
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);
28 static int stopmachine(void *cpu)
30 int irqs_disabled = 0;
33 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
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);
39 /* Simple state machine */
40 while (stopmachine_state != STOPMACHINE_EXIT) {
41 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
45 /* Ack: irqs disabled. */
46 smp_mb(); /* Must read state first. */
47 atomic_inc(&stopmachine_thread_ack);
48 } else if (stopmachine_state == STOPMACHINE_PREPARE
50 /* Everyone is in place, hold CPU. */
53 smp_mb(); /* Must read state first. */
54 atomic_inc(&stopmachine_thread_ack);
56 /* Yield in first stage: migration threads need to
57 * help our sisters onto their CPUs. */
58 if (!prepared && !irqs_disabled)
64 /* Ack: we are exiting. */
65 smp_mb(); /* Must read state first. */
66 atomic_inc(&stopmachine_thread_ack);
76 /* Change the thread state */
77 static void stopmachine_set_state(enum stopmachine_state state)
79 atomic_set(&stopmachine_thread_ack, 0);
81 stopmachine_state = state;
82 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
86 static int stop_machine(void)
89 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
91 /* One high-prio thread per cpu. We'll do this one. */
92 sched_setscheduler(current, SCHED_FIFO, ¶m);
94 atomic_set(&stopmachine_thread_ack, 0);
95 stopmachine_num_threads = 0;
96 stopmachine_state = STOPMACHINE_WAIT;
98 for_each_online_cpu(i) {
99 if (i == raw_smp_processor_id())
101 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
104 stopmachine_num_threads++;
107 /* Wait for them all to come to life. */
108 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
111 /* If some failed, kill them all. */
113 stopmachine_set_state(STOPMACHINE_EXIT);
117 /* Now they are all started, make them hold the CPUs, ready. */
119 stopmachine_set_state(STOPMACHINE_PREPARE);
121 /* Make them disable irqs. */
123 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
128 static void restart_machine(void)
130 stopmachine_set_state(STOPMACHINE_EXIT);
132 preempt_enable_no_resched();
135 struct stop_machine_data
139 struct completion done;
142 static int do_stop(void *_smdata)
144 struct stop_machine_data *smdata = _smdata;
147 ret = stop_machine();
149 ret = smdata->fn(smdata->data);
153 /* We're done: you can kthread_stop us now */
154 complete(&smdata->done);
156 /* Wait for kthread_stop */
157 set_current_state(TASK_INTERRUPTIBLE);
158 while (!kthread_should_stop()) {
160 set_current_state(TASK_INTERRUPTIBLE);
162 __set_current_state(TASK_RUNNING);
166 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
169 struct stop_machine_data smdata;
170 struct task_struct *p;
174 init_completion(&smdata.done);
176 down(&stopmachine_mutex);
178 /* If they don't care which CPU fn runs on, bind to any online one. */
180 cpu = raw_smp_processor_id();
182 p = kthread_create(do_stop, &smdata, "kstopmachine");
184 kthread_bind(p, cpu);
186 wait_for_completion(&smdata.done);
188 up(&stopmachine_mutex);
192 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
194 struct task_struct *p;
197 /* No CPUs can come up or down during this. */
199 p = __stop_machine_run(fn, data, cpu);
201 ret = kthread_stop(p);
204 unlock_cpu_hotplug();