[PATCH] stop_machine.c copyright
[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/stop_machine.h>
5 #include <linux/kthread.h>
6 #include <linux/sched.h>
7 #include <linux/cpu.h>
8 #include <linux/err.h>
9 #include <linux/syscalls.h>
10 #include <asm/atomic.h>
11 #include <asm/semaphore.h>
12 #include <asm/uaccess.h>
13
14 /* Since we effect priority and affinity (both of which are visible
15  * to, and settable by outside processes) we do indirection via a
16  * kthread. */
17
18 /* Thread to stop each CPU in user context. */
19 enum stopmachine_state {
20         STOPMACHINE_WAIT,
21         STOPMACHINE_PREPARE,
22         STOPMACHINE_DISABLE_IRQ,
23         STOPMACHINE_EXIT,
24 };
25
26 static enum stopmachine_state stopmachine_state;
27 static unsigned int stopmachine_num_threads;
28 static atomic_t stopmachine_thread_ack;
29 static DECLARE_MUTEX(stopmachine_mutex);
30
31 static int stopmachine(void *cpu)
32 {
33         int irqs_disabled = 0;
34         int prepared = 0;
35
36         set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
37
38         /* Ack: we are alive */
39         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
40         atomic_inc(&stopmachine_thread_ack);
41
42         /* Simple state machine */
43         while (stopmachine_state != STOPMACHINE_EXIT) {
44                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 
45                     && !irqs_disabled) {
46                         local_irq_disable();
47                         irqs_disabled = 1;
48                         /* Ack: irqs disabled. */
49                         smp_mb(); /* Must read state first. */
50                         atomic_inc(&stopmachine_thread_ack);
51                 } else if (stopmachine_state == STOPMACHINE_PREPARE
52                            && !prepared) {
53                         /* Everyone is in place, hold CPU. */
54                         preempt_disable();
55                         prepared = 1;
56                         smp_mb(); /* Must read state first. */
57                         atomic_inc(&stopmachine_thread_ack);
58                 }
59                 /* Yield in first stage: migration threads need to
60                  * help our sisters onto their CPUs. */
61                 if (!prepared && !irqs_disabled)
62                         yield();
63                 else
64                         cpu_relax();
65         }
66
67         /* Ack: we are exiting. */
68         smp_mb(); /* Must read state first. */
69         atomic_inc(&stopmachine_thread_ack);
70
71         if (irqs_disabled)
72                 local_irq_enable();
73         if (prepared)
74                 preempt_enable();
75
76         return 0;
77 }
78
79 /* Change the thread state */
80 static void stopmachine_set_state(enum stopmachine_state state)
81 {
82         atomic_set(&stopmachine_thread_ack, 0);
83         smp_wmb();
84         stopmachine_state = state;
85         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
86                 cpu_relax();
87 }
88
89 static int stop_machine(void)
90 {
91         int i, ret = 0;
92         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
93
94         /* One high-prio thread per cpu.  We'll do this one. */
95         sched_setscheduler(current, SCHED_FIFO, &param);
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         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 {
140         int (*fn)(void *);
141         void *data;
142         struct completion done;
143 };
144
145 static int do_stop(void *_smdata)
146 {
147         struct stop_machine_data *smdata = _smdata;
148         int ret;
149
150         ret = stop_machine();
151         if (ret == 0) {
152                 ret = smdata->fn(smdata->data);
153                 restart_machine();
154         }
155
156         /* We're done: you can kthread_stop us now */
157         complete(&smdata->done);
158
159         /* Wait for kthread_stop */
160         set_current_state(TASK_INTERRUPTIBLE);
161         while (!kthread_should_stop()) {
162                 schedule();
163                 set_current_state(TASK_INTERRUPTIBLE);
164         }
165         __set_current_state(TASK_RUNNING);
166         return ret;
167 }
168
169 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
170                                        unsigned int cpu)
171 {
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         down(&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                 kthread_bind(p, cpu);
188                 wake_up_process(p);
189                 wait_for_completion(&smdata.done);
190         }
191         up(&stopmachine_mutex);
192         return p;
193 }
194
195 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
196 {
197         struct task_struct *p;
198         int ret;
199
200         /* No CPUs can come up or down during this. */
201         lock_cpu_hotplug();
202         p = __stop_machine_run(fn, data, cpu);
203         if (!IS_ERR(p))
204                 ret = kthread_stop(p);
205         else
206                 ret = PTR_ERR(p);
207         unlock_cpu_hotplug();
208
209         return ret;
210 }