stop_machine: remove unused variable
[linux-2.6.git] / kernel / stop_machine.c
1 /* Copyright 2008, 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 /* This controls the threads on each CPU. */
17 enum stopmachine_state {
18         /* Dummy starting state for thread. */
19         STOPMACHINE_NONE,
20         /* Awaiting everyone to be scheduled. */
21         STOPMACHINE_PREPARE,
22         /* Disable interrupts. */
23         STOPMACHINE_DISABLE_IRQ,
24         /* Run the function */
25         STOPMACHINE_RUN,
26         /* Exit */
27         STOPMACHINE_EXIT,
28 };
29 static enum stopmachine_state state;
30
31 struct stop_machine_data {
32         int (*fn)(void *);
33         void *data;
34         int fnret;
35 };
36
37 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
38 static unsigned int num_threads;
39 static atomic_t thread_ack;
40 static struct completion finished;
41 static DEFINE_MUTEX(lock);
42
43 static void set_state(enum stopmachine_state newstate)
44 {
45         /* Reset ack counter. */
46         atomic_set(&thread_ack, num_threads);
47         smp_wmb();
48         state = newstate;
49 }
50
51 /* Last one to ack a state moves to the next state. */
52 static void ack_state(void)
53 {
54         if (atomic_dec_and_test(&thread_ack)) {
55                 /* If we're the last one to ack the EXIT, we're finished. */
56                 if (state == STOPMACHINE_EXIT)
57                         complete(&finished);
58                 else
59                         set_state(state + 1);
60         }
61 }
62
63 /* This is the actual thread which stops the CPU.  It exits by itself rather
64  * than waiting for kthread_stop(), because it's easier for hotplug CPU. */
65 static int stop_cpu(struct stop_machine_data *smdata)
66 {
67         enum stopmachine_state curstate = STOPMACHINE_NONE;
68
69         /* Simple state machine */
70         do {
71                 /* Chill out and ensure we re-read stopmachine_state. */
72                 cpu_relax();
73                 if (state != curstate) {
74                         curstate = state;
75                         switch (curstate) {
76                         case STOPMACHINE_DISABLE_IRQ:
77                                 local_irq_disable();
78                                 hard_irq_disable();
79                                 break;
80                         case STOPMACHINE_RUN:
81                                 /* |= allows error detection if functions on
82                                  * multiple CPUs. */
83                                 smdata->fnret |= smdata->fn(smdata->data);
84                                 break;
85                         default:
86                                 break;
87                         }
88                         ack_state();
89                 }
90         } while (curstate != STOPMACHINE_EXIT);
91
92         local_irq_enable();
93         do_exit(0);
94 }
95
96 /* Callback for CPUs which aren't supposed to do anything. */
97 static int chill(void *unused)
98 {
99         return 0;
100 }
101
102 int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
103 {
104         int i, err;
105         struct stop_machine_data active, idle;
106         struct task_struct **threads;
107
108         active.fn = fn;
109         active.data = data;
110         active.fnret = 0;
111         idle.fn = chill;
112         idle.data = NULL;
113
114         /* This could be too big for stack on large machines. */
115         threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
116         if (!threads)
117                 return -ENOMEM;
118
119         /* Set up initial state. */
120         mutex_lock(&lock);
121         init_completion(&finished);
122         num_threads = num_online_cpus();
123         set_state(STOPMACHINE_PREPARE);
124
125         for_each_online_cpu(i) {
126                 struct stop_machine_data *smdata = &idle;
127                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
128
129                 if (!cpus) {
130                         if (i == first_cpu(cpu_online_map))
131                                 smdata = &active;
132                 } else {
133                         if (cpu_isset(i, *cpus))
134                                 smdata = &active;
135                 }
136
137                 threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
138                                             i);
139                 if (IS_ERR(threads[i])) {
140                         err = PTR_ERR(threads[i]);
141                         threads[i] = NULL;
142                         goto kill_threads;
143                 }
144
145                 /* Place it onto correct cpu. */
146                 kthread_bind(threads[i], i);
147
148                 /* Make it highest prio. */
149                 if (sched_setscheduler_nocheck(threads[i], SCHED_FIFO, &param))
150                         BUG();
151         }
152
153         /* We've created all the threads.  Wake them all: hold this CPU so one
154          * doesn't hit this CPU until we're ready. */
155         get_cpu();
156         for_each_online_cpu(i)
157                 wake_up_process(threads[i]);
158
159         /* This will release the thread on our CPU. */
160         put_cpu();
161         wait_for_completion(&finished);
162         mutex_unlock(&lock);
163
164         kfree(threads);
165
166         return active.fnret;
167
168 kill_threads:
169         for_each_online_cpu(i)
170                 if (threads[i])
171                         kthread_stop(threads[i]);
172         mutex_unlock(&lock);
173
174         kfree(threads);
175         return err;
176 }
177
178 int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
179 {
180         int ret;
181
182         /* No CPUs can come up or down during this. */
183         get_online_cpus();
184         ret = __stop_machine(fn, data, cpus);
185         put_online_cpus();
186
187         return ret;
188 }
189 EXPORT_SYMBOL_GPL(stop_machine);