cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus()
[linux-2.6.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 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, &param);
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         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);