DOC: A couple corrections and clarifications in USB doc.
[linux-3.10.git] / kernel / stop_machine.c
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         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, &param);
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);