[PATCH] kthread: convert stop_machine into a kthread
[linux-2.6.git] / kernel / stop_machine.c
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 <linux/kthread.h>
8 #include <asm/atomic.h>
9 #include <asm/semaphore.h>
10 #include <asm/uaccess.h>
11
12 /* Since we effect priority and affinity (both of which are visible
13  * to, and settable by outside processes) we do indirection via a
14  * kthread. */
15
16 /* Thread to stop each CPU in user context. */
17 enum stopmachine_state {
18         STOPMACHINE_WAIT,
19         STOPMACHINE_PREPARE,
20         STOPMACHINE_DISABLE_IRQ,
21         STOPMACHINE_EXIT,
22 };
23
24 static enum stopmachine_state stopmachine_state;
25 static unsigned int stopmachine_num_threads;
26 static atomic_t stopmachine_thread_ack;
27 static DECLARE_MUTEX(stopmachine_mutex);
28
29 static int stopmachine(void *unused)
30 {
31         int irqs_disabled = 0;
32         int prepared = 0;
33
34         /* Ack: we are alive */
35         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
36         atomic_inc(&stopmachine_thread_ack);
37
38         /* Simple state machine */
39         while (stopmachine_state != STOPMACHINE_EXIT) {
40                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 
41                     && !irqs_disabled) {
42                         local_irq_disable();
43                         irqs_disabled = 1;
44                         /* Ack: irqs disabled. */
45                         smp_mb(); /* Must read state first. */
46                         atomic_inc(&stopmachine_thread_ack);
47                 } else if (stopmachine_state == STOPMACHINE_PREPARE
48                            && !prepared) {
49                         /* Everyone is in place, hold CPU. */
50                         preempt_disable();
51                         prepared = 1;
52                         smp_mb(); /* Must read state first. */
53                         atomic_inc(&stopmachine_thread_ack);
54                 }
55                 /* Yield in first stage: migration threads need to
56                  * help our sisters onto their CPUs. */
57                 if (!prepared && !irqs_disabled)
58                         yield();
59                 else
60                         cpu_relax();
61         }
62
63         /* Ack: we are exiting. */
64         smp_mb(); /* Must read state first. */
65         atomic_inc(&stopmachine_thread_ack);
66
67         if (irqs_disabled)
68                 local_irq_enable();
69         if (prepared)
70                 preempt_enable();
71
72         return 0;
73 }
74
75 /* Change the thread state */
76 static void stopmachine_set_state(enum stopmachine_state state)
77 {
78         atomic_set(&stopmachine_thread_ack, 0);
79         smp_wmb();
80         stopmachine_state = state;
81         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
82                 cpu_relax();
83 }
84
85 static int stop_machine(void)
86 {
87         int ret = 0;
88         unsigned int i;
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, &param);
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                 struct task_struct *tsk;
100                 if (i == raw_smp_processor_id())
101                         continue;
102                 tsk = kthread_create(stopmachine, NULL, "stopmachine");
103                 if (IS_ERR(tsk)) {
104                         ret = PTR_ERR(tsk);
105                         break;
106                 }
107                 kthread_bind(tsk, i);
108                 wake_up_process(tsk);
109                 stopmachine_num_threads++;
110         }
111
112         /* Wait for them all to come to life. */
113         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
114                 yield();
115
116         /* If some failed, kill them all. */
117         if (ret < 0) {
118                 stopmachine_set_state(STOPMACHINE_EXIT);
119                 up(&stopmachine_mutex);
120                 return ret;
121         }
122
123         /* Now they are all started, make them hold the CPUs, ready. */
124         preempt_disable();
125         stopmachine_set_state(STOPMACHINE_PREPARE);
126
127         /* Make them disable irqs. */
128         local_irq_disable();
129         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
130
131         return 0;
132 }
133
134 static void restart_machine(void)
135 {
136         stopmachine_set_state(STOPMACHINE_EXIT);
137         local_irq_enable();
138         preempt_enable_no_resched();
139 }
140
141 struct stop_machine_data
142 {
143         int (*fn)(void *);
144         void *data;
145         struct completion done;
146 };
147
148 static int do_stop(void *_smdata)
149 {
150         struct stop_machine_data *smdata = _smdata;
151         int ret;
152
153         ret = stop_machine();
154         if (ret == 0) {
155                 ret = smdata->fn(smdata->data);
156                 restart_machine();
157         }
158
159         /* We're done: you can kthread_stop us now */
160         complete(&smdata->done);
161
162         /* Wait for kthread_stop */
163         set_current_state(TASK_INTERRUPTIBLE);
164         while (!kthread_should_stop()) {
165                 schedule();
166                 set_current_state(TASK_INTERRUPTIBLE);
167         }
168         __set_current_state(TASK_RUNNING);
169         return ret;
170 }
171
172 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
173                                        unsigned int cpu)
174 {
175         struct stop_machine_data smdata;
176         struct task_struct *p;
177
178         smdata.fn = fn;
179         smdata.data = data;
180         init_completion(&smdata.done);
181
182         down(&stopmachine_mutex);
183
184         /* If they don't care which CPU fn runs on, bind to any online one. */
185         if (cpu == NR_CPUS)
186                 cpu = raw_smp_processor_id();
187
188         p = kthread_create(do_stop, &smdata, "kstopmachine");
189         if (!IS_ERR(p)) {
190                 kthread_bind(p, cpu);
191                 wake_up_process(p);
192                 wait_for_completion(&smdata.done);
193         }
194         up(&stopmachine_mutex);
195         return p;
196 }
197
198 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
199 {
200         struct task_struct *p;
201         int ret;
202
203         /* No CPUs can come up or down during this. */
204         lock_cpu_hotplug();
205         p = __stop_machine_run(fn, data, cpu);
206         if (!IS_ERR(p))
207                 ret = kthread_stop(p);
208         else
209                 ret = PTR_ERR(p);
210         unlock_cpu_hotplug();
211
212         return ret;
213 }