Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/juhl/trivial
[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/uaccess.h>
15
16 /* Since we effect priority and affinity (both of which are visible
17  * to, and settable by outside processes) we do indirection via a
18  * kthread. */
19
20 /* Thread to stop each CPU in user context. */
21 enum stopmachine_state {
22         STOPMACHINE_WAIT,
23         STOPMACHINE_PREPARE,
24         STOPMACHINE_DISABLE_IRQ,
25         STOPMACHINE_EXIT,
26 };
27
28 static enum stopmachine_state stopmachine_state;
29 static unsigned int stopmachine_num_threads;
30 static atomic_t stopmachine_thread_ack;
31
32 static int stopmachine(void *cpu)
33 {
34         int irqs_disabled = 0;
35         int prepared = 0;
36
37         set_cpus_allowed_ptr(current, &cpumask_of_cpu((int)(long)cpu));
38
39         /* Ack: we are alive */
40         smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
41         atomic_inc(&stopmachine_thread_ack);
42
43         /* Simple state machine */
44         while (stopmachine_state != STOPMACHINE_EXIT) {
45                 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 
46                     && !irqs_disabled) {
47                         local_irq_disable();
48                         hard_irq_disable();
49                         irqs_disabled = 1;
50                         /* Ack: irqs disabled. */
51                         smp_mb(); /* Must read state first. */
52                         atomic_inc(&stopmachine_thread_ack);
53                 } else if (stopmachine_state == STOPMACHINE_PREPARE
54                            && !prepared) {
55                         /* Everyone is in place, hold CPU. */
56                         preempt_disable();
57                         prepared = 1;
58                         smp_mb(); /* Must read state first. */
59                         atomic_inc(&stopmachine_thread_ack);
60                 }
61                 /* Yield in first stage: migration threads need to
62                  * help our sisters onto their CPUs. */
63                 if (!prepared && !irqs_disabled)
64                         yield();
65                 else
66                         cpu_relax();
67         }
68
69         /* Ack: we are exiting. */
70         smp_mb(); /* Must read state first. */
71         atomic_inc(&stopmachine_thread_ack);
72
73         if (irqs_disabled)
74                 local_irq_enable();
75         if (prepared)
76                 preempt_enable();
77
78         return 0;
79 }
80
81 /* Change the thread state */
82 static void stopmachine_set_state(enum stopmachine_state state)
83 {
84         atomic_set(&stopmachine_thread_ack, 0);
85         smp_wmb();
86         stopmachine_state = state;
87         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
88                 cpu_relax();
89 }
90
91 static int stop_machine(void)
92 {
93         int i, ret = 0;
94
95         atomic_set(&stopmachine_thread_ack, 0);
96         stopmachine_num_threads = 0;
97         stopmachine_state = STOPMACHINE_WAIT;
98
99         for_each_online_cpu(i) {
100                 if (i == raw_smp_processor_id())
101                         continue;
102                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
103                 if (ret < 0)
104                         break;
105                 stopmachine_num_threads++;
106         }
107
108         /* Wait for them all to come to life. */
109         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
110                 yield();
111
112         /* If some failed, kill them all. */
113         if (ret < 0) {
114                 stopmachine_set_state(STOPMACHINE_EXIT);
115                 return ret;
116         }
117
118         /* Now they are all started, make them hold the CPUs, ready. */
119         preempt_disable();
120         stopmachine_set_state(STOPMACHINE_PREPARE);
121
122         /* Make them disable irqs. */
123         local_irq_disable();
124         hard_irq_disable();
125         stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
126
127         return 0;
128 }
129
130 static void restart_machine(void)
131 {
132         stopmachine_set_state(STOPMACHINE_EXIT);
133         local_irq_enable();
134         preempt_enable_no_resched();
135 }
136
137 struct stop_machine_data {
138         int (*fn)(void *);
139         void *data;
140         struct completion done;
141 };
142
143 static int do_stop(void *_smdata)
144 {
145         struct stop_machine_data *smdata = _smdata;
146         int ret;
147
148         ret = stop_machine();
149         if (ret == 0) {
150                 ret = smdata->fn(smdata->data);
151                 restart_machine();
152         }
153
154         /* We're done: you can kthread_stop us now */
155         complete(&smdata->done);
156
157         /* Wait for kthread_stop */
158         set_current_state(TASK_INTERRUPTIBLE);
159         while (!kthread_should_stop()) {
160                 schedule();
161                 set_current_state(TASK_INTERRUPTIBLE);
162         }
163         __set_current_state(TASK_RUNNING);
164         return ret;
165 }
166
167 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
168                                        unsigned int cpu)
169 {
170         static DEFINE_MUTEX(stopmachine_mutex);
171         struct stop_machine_data smdata;
172         struct task_struct *p;
173
174         smdata.fn = fn;
175         smdata.data = data;
176         init_completion(&smdata.done);
177
178         mutex_lock(&stopmachine_mutex);
179
180         /* If they don't care which CPU fn runs on, bind to any online one. */
181         if (cpu == NR_CPUS)
182                 cpu = raw_smp_processor_id();
183
184         p = kthread_create(do_stop, &smdata, "kstopmachine");
185         if (!IS_ERR(p)) {
186                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
187
188                 /* One high-prio thread per cpu.  We'll do this one. */
189                 sched_setscheduler(p, SCHED_FIFO, &param);
190                 kthread_bind(p, cpu);
191                 wake_up_process(p);
192                 wait_for_completion(&smdata.done);
193         }
194         mutex_unlock(&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         get_online_cpus();
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         put_online_cpus();
211
212         return ret;
213 }
214 EXPORT_SYMBOL_GPL(stop_machine_run);