Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes...
[linux-2.6] / 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 DEFINE_MUTEX(lock);
41
42 static struct workqueue_struct *stop_machine_wq;
43 static struct stop_machine_data active, idle;
44 static const cpumask_t *active_cpus;
45 static void *stop_machine_work;
46
47 static void set_state(enum stopmachine_state newstate)
48 {
49         /* Reset ack counter. */
50         atomic_set(&thread_ack, num_threads);
51         smp_wmb();
52         state = newstate;
53 }
54
55 /* Last one to ack a state moves to the next state. */
56 static void ack_state(void)
57 {
58         if (atomic_dec_and_test(&thread_ack))
59                 set_state(state + 1);
60 }
61
62 /* This is the actual function which stops the CPU. It runs
63  * in the context of a dedicated stopmachine workqueue. */
64 static void stop_cpu(struct work_struct *unused)
65 {
66         enum stopmachine_state curstate = STOPMACHINE_NONE;
67         struct stop_machine_data *smdata = &idle;
68         int cpu = smp_processor_id();
69         int err;
70
71         if (!active_cpus) {
72                 if (cpu == first_cpu(cpu_online_map))
73                         smdata = &active;
74         } else {
75                 if (cpu_isset(cpu, *active_cpus))
76                         smdata = &active;
77         }
78         /* Simple state machine */
79         do {
80                 /* Chill out and ensure we re-read stopmachine_state. */
81                 cpu_relax();
82                 if (state != curstate) {
83                         curstate = state;
84                         switch (curstate) {
85                         case STOPMACHINE_DISABLE_IRQ:
86                                 local_irq_disable();
87                                 hard_irq_disable();
88                                 break;
89                         case STOPMACHINE_RUN:
90                                 /* On multiple CPUs only a single error code
91                                  * is needed to tell that something failed. */
92                                 err = smdata->fn(smdata->data);
93                                 if (err)
94                                         smdata->fnret = err;
95                                 break;
96                         default:
97                                 break;
98                         }
99                         ack_state();
100                 }
101         } while (curstate != STOPMACHINE_EXIT);
102
103         local_irq_enable();
104 }
105
106 /* Callback for CPUs which aren't supposed to do anything. */
107 static int chill(void *unused)
108 {
109         return 0;
110 }
111
112 int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
113 {
114         struct work_struct *sm_work;
115         int i, ret;
116
117         /* Set up initial state. */
118         mutex_lock(&lock);
119         num_threads = num_online_cpus();
120         active_cpus = cpus;
121         active.fn = fn;
122         active.data = data;
123         active.fnret = 0;
124         idle.fn = chill;
125         idle.data = NULL;
126
127         set_state(STOPMACHINE_PREPARE);
128
129         /* Schedule the stop_cpu work on all cpus: hold this CPU so one
130          * doesn't hit this CPU until we're ready. */
131         get_cpu();
132         for_each_online_cpu(i) {
133                 sm_work = percpu_ptr(stop_machine_work, i);
134                 INIT_WORK(sm_work, stop_cpu);
135                 queue_work_on(i, stop_machine_wq, sm_work);
136         }
137         /* This will release the thread on our CPU. */
138         put_cpu();
139         flush_workqueue(stop_machine_wq);
140         ret = active.fnret;
141         mutex_unlock(&lock);
142         return ret;
143 }
144
145 int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
146 {
147         int ret;
148
149         /* No CPUs can come up or down during this. */
150         get_online_cpus();
151         ret = __stop_machine(fn, data, cpus);
152         put_online_cpus();
153
154         return ret;
155 }
156 EXPORT_SYMBOL_GPL(stop_machine);
157
158 static int __init stop_machine_init(void)
159 {
160         stop_machine_wq = create_rt_workqueue("kstop");
161         stop_machine_work = alloc_percpu(struct work_struct);
162         return 0;
163 }
164 core_initcall(stop_machine_init);