Use stop_machine_run in the Intel RNG driver
[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 <asm/atomic.h>
12 #include <asm/semaphore.h>
13 #include <asm/uaccess.h>
14
15 /* Since we effect priority and affinity (both of which are visible
16  * to, and settable by outside processes) we do indirection via a
17  * kthread. */
18
19 /* Thread to stop each CPU in user context. */
20 enum stopmachine_state {
21         STOPMACHINE_WAIT,
22         STOPMACHINE_PREPARE,
23         STOPMACHINE_DISABLE_IRQ,
24         STOPMACHINE_EXIT,
25 };
26
27 static enum stopmachine_state stopmachine_state;
28 static unsigned int stopmachine_num_threads;
29 static atomic_t stopmachine_thread_ack;
30 static DECLARE_MUTEX(stopmachine_mutex);
31
32 static int stopmachine(void *cpu)
33 {
34         int irqs_disabled = 0;
35         int prepared = 0;
36
37         set_cpus_allowed(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                         irqs_disabled = 1;
49                         /* Ack: irqs disabled. */
50                         smp_mb(); /* Must read state first. */
51                         atomic_inc(&stopmachine_thread_ack);
52                 } else if (stopmachine_state == STOPMACHINE_PREPARE
53                            && !prepared) {
54                         /* Everyone is in place, hold CPU. */
55                         preempt_disable();
56                         prepared = 1;
57                         smp_mb(); /* Must read state first. */
58                         atomic_inc(&stopmachine_thread_ack);
59                 }
60                 /* Yield in first stage: migration threads need to
61                  * help our sisters onto their CPUs. */
62                 if (!prepared && !irqs_disabled)
63                         yield();
64                 else
65                         cpu_relax();
66         }
67
68         /* Ack: we are exiting. */
69         smp_mb(); /* Must read state first. */
70         atomic_inc(&stopmachine_thread_ack);
71
72         if (irqs_disabled)
73                 local_irq_enable();
74         if (prepared)
75                 preempt_enable();
76
77         return 0;
78 }
79
80 /* Change the thread state */
81 static void stopmachine_set_state(enum stopmachine_state state)
82 {
83         atomic_set(&stopmachine_thread_ack, 0);
84         smp_wmb();
85         stopmachine_state = state;
86         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
87                 cpu_relax();
88 }
89
90 static int stop_machine(void)
91 {
92         int i, ret = 0;
93         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
94
95         /* One high-prio thread per cpu.  We'll do this one. */
96         sched_setscheduler(current, SCHED_FIFO, &param);
97
98         atomic_set(&stopmachine_thread_ack, 0);
99         stopmachine_num_threads = 0;
100         stopmachine_state = STOPMACHINE_WAIT;
101
102         for_each_online_cpu(i) {
103                 if (i == raw_smp_processor_id())
104                         continue;
105                 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
106                 if (ret < 0)
107                         break;
108                 stopmachine_num_threads++;
109         }
110
111         /* Wait for them all to come to life. */
112         while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
113                 yield();
114
115         /* If some failed, kill them all. */
116         if (ret < 0) {
117                 stopmachine_set_state(STOPMACHINE_EXIT);
118                 return ret;
119         }
120
121         /* Now they are all started, make them hold the CPUs, ready. */
122         preempt_disable();
123         stopmachine_set_state(STOPMACHINE_PREPARE);
124
125         /* Make them disable irqs. */
126         local_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                 kthread_bind(p, cpu);
189                 wake_up_process(p);
190                 wait_for_completion(&smdata.done);
191         }
192         up(&stopmachine_mutex);
193         return p;
194 }
195
196 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
197 {
198         struct task_struct *p;
199         int ret;
200
201         /* No CPUs can come up or down during this. */
202         lock_cpu_hotplug();
203         p = __stop_machine_run(fn, data, cpu);
204         if (!IS_ERR(p))
205                 ret = kthread_stop(p);
206         else
207                 ret = PTR_ERR(p);
208         unlock_cpu_hotplug();
209
210         return ret;
211 }
212 EXPORT_SYMBOL_GPL(stop_machine_run);