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Linus Torvalds1da177e2005-04-16 15:20:36 -07001#include <linux/stop_machine.h>
2#include <linux/kthread.h>
3#include <linux/sched.h>
4#include <linux/cpu.h>
5#include <linux/err.h>
6#include <linux/syscalls.h>
7#include <asm/atomic.h>
8#include <asm/semaphore.h>
9#include <asm/uaccess.h>
10
11/* Since we effect priority and affinity (both of which are visible
12 * to, and settable by outside processes) we do indirection via a
13 * kthread. */
14
15/* Thread to stop each CPU in user context. */
16enum stopmachine_state {
17 STOPMACHINE_WAIT,
18 STOPMACHINE_PREPARE,
19 STOPMACHINE_DISABLE_IRQ,
20 STOPMACHINE_EXIT,
21};
22
23static enum stopmachine_state stopmachine_state;
24static unsigned int stopmachine_num_threads;
25static atomic_t stopmachine_thread_ack;
26static DECLARE_MUTEX(stopmachine_mutex);
27
Andrew Mortond8cb7c12006-07-03 17:32:22 -070028static int stopmachine(void *cpu)
Linus Torvalds1da177e2005-04-16 15:20:36 -070029{
30 int irqs_disabled = 0;
31 int prepared = 0;
32
Andrew Mortond8cb7c12006-07-03 17:32:22 -070033 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
34
Linus Torvalds1da177e2005-04-16 15:20:36 -070035 /* Ack: we are alive */
akpm@osdl.orgd59dd462005-05-01 08:58:47 -070036 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
Linus Torvalds1da177e2005-04-16 15:20:36 -070037 atomic_inc(&stopmachine_thread_ack);
38
39 /* Simple state machine */
40 while (stopmachine_state != STOPMACHINE_EXIT) {
41 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
42 && !irqs_disabled) {
43 local_irq_disable();
44 irqs_disabled = 1;
45 /* Ack: irqs disabled. */
akpm@osdl.orgd59dd462005-05-01 08:58:47 -070046 smp_mb(); /* Must read state first. */
Linus Torvalds1da177e2005-04-16 15:20:36 -070047 atomic_inc(&stopmachine_thread_ack);
48 } else if (stopmachine_state == STOPMACHINE_PREPARE
49 && !prepared) {
50 /* Everyone is in place, hold CPU. */
51 preempt_disable();
52 prepared = 1;
akpm@osdl.orgd59dd462005-05-01 08:58:47 -070053 smp_mb(); /* Must read state first. */
Linus Torvalds1da177e2005-04-16 15:20:36 -070054 atomic_inc(&stopmachine_thread_ack);
55 }
56 /* Yield in first stage: migration threads need to
57 * help our sisters onto their CPUs. */
58 if (!prepared && !irqs_disabled)
59 yield();
60 else
61 cpu_relax();
62 }
63
64 /* Ack: we are exiting. */
akpm@osdl.orgd59dd462005-05-01 08:58:47 -070065 smp_mb(); /* Must read state first. */
Linus Torvalds1da177e2005-04-16 15:20:36 -070066 atomic_inc(&stopmachine_thread_ack);
67
68 if (irqs_disabled)
69 local_irq_enable();
70 if (prepared)
71 preempt_enable();
72
73 return 0;
74}
75
76/* Change the thread state */
77static void stopmachine_set_state(enum stopmachine_state state)
78{
79 atomic_set(&stopmachine_thread_ack, 0);
akpm@osdl.orgd59dd462005-05-01 08:58:47 -070080 smp_wmb();
Linus Torvalds1da177e2005-04-16 15:20:36 -070081 stopmachine_state = state;
82 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
83 cpu_relax();
84}
85
86static int stop_machine(void)
87{
Andrew Mortond8cb7c12006-07-03 17:32:22 -070088 int i, ret = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
Linus Torvalds1da177e2005-04-16 15:20:36 -070090
91 /* One high-prio thread per cpu. We'll do this one. */
akpm@osdl.orged653a62006-01-09 20:51:38 -080092 sched_setscheduler(current, SCHED_FIFO, &param);
Linus Torvalds1da177e2005-04-16 15:20:36 -070093
94 atomic_set(&stopmachine_thread_ack, 0);
95 stopmachine_num_threads = 0;
96 stopmachine_state = STOPMACHINE_WAIT;
97
98 for_each_online_cpu(i) {
Ingo Molnar39c715b2005-06-21 17:14:34 -070099 if (i == raw_smp_processor_id())
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 continue;
Andrew Mortond8cb7c12006-07-03 17:32:22 -0700101 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
102 if (ret < 0)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103 break;
104 stopmachine_num_threads++;
105 }
106
107 /* Wait for them all to come to life. */
108 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
109 yield();
110
111 /* If some failed, kill them all. */
112 if (ret < 0) {
113 stopmachine_set_state(STOPMACHINE_EXIT);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 return ret;
115 }
116
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117 /* Now they are all started, make them hold the CPUs, ready. */
Kirill Korotaev45573982005-11-13 16:07:30 -0800118 preempt_disable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119 stopmachine_set_state(STOPMACHINE_PREPARE);
120
121 /* Make them disable irqs. */
Kirill Korotaev45573982005-11-13 16:07:30 -0800122 local_irq_disable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700123 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
124
125 return 0;
126}
127
128static void restart_machine(void)
129{
130 stopmachine_set_state(STOPMACHINE_EXIT);
131 local_irq_enable();
Kirill Korotaev45573982005-11-13 16:07:30 -0800132 preempt_enable_no_resched();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133}
134
135struct stop_machine_data
136{
137 int (*fn)(void *);
138 void *data;
139 struct completion done;
140};
141
142static int do_stop(void *_smdata)
143{
144 struct stop_machine_data *smdata = _smdata;
145 int ret;
146
147 ret = stop_machine();
148 if (ret == 0) {
149 ret = smdata->fn(smdata->data);
150 restart_machine();
151 }
152
153 /* We're done: you can kthread_stop us now */
154 complete(&smdata->done);
155
156 /* Wait for kthread_stop */
157 set_current_state(TASK_INTERRUPTIBLE);
158 while (!kthread_should_stop()) {
159 schedule();
160 set_current_state(TASK_INTERRUPTIBLE);
161 }
162 __set_current_state(TASK_RUNNING);
163 return ret;
164}
165
166struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
167 unsigned int cpu)
168{
169 struct stop_machine_data smdata;
170 struct task_struct *p;
171
172 smdata.fn = fn;
173 smdata.data = data;
174 init_completion(&smdata.done);
175
176 down(&stopmachine_mutex);
177
178 /* If they don't care which CPU fn runs on, bind to any online one. */
179 if (cpu == NR_CPUS)
Ingo Molnar39c715b2005-06-21 17:14:34 -0700180 cpu = raw_smp_processor_id();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181
182 p = kthread_create(do_stop, &smdata, "kstopmachine");
183 if (!IS_ERR(p)) {
184 kthread_bind(p, cpu);
185 wake_up_process(p);
186 wait_for_completion(&smdata.done);
187 }
188 up(&stopmachine_mutex);
189 return p;
190}
191
192int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
193{
194 struct task_struct *p;
195 int ret;
196
197 /* No CPUs can come up or down during this. */
198 lock_cpu_hotplug();
199 p = __stop_machine_run(fn, data, cpu);
200 if (!IS_ERR(p))
201 ret = kthread_stop(p);
202 else
203 ret = PTR_ERR(p);
204 unlock_cpu_hotplug();
205
206 return ret;
207}