projects/linux·blob v2.6.19-rc6 · refs

210 lines · 4.8 KiB

1/* Copyright 2005 Rusty Russell [email protected] IBM Corporation.
2 * GPL v2 and any later version.
3 */
4#include <linux/stop_machine.h>
5#include <linux/kthread.h>
6#include <linux/sched.h>
7#include <linux/cpu.h>
8#include <linux/err.h>
9#include <linux/syscalls.h>
10#include <asm/atomic.h>
11#include <asm/semaphore.h>
12#include <asm/uaccess.h>
13
14/* Since we effect priority and affinity (both of which are visible
15 * to, and settable by outside processes) we do indirection via a
16 * kthread. */
17
18/* Thread to stop each CPU in user context. */
19enum stopmachine_state {
20 STOPMACHINE_WAIT,
21 STOPMACHINE_PREPARE,
22 STOPMACHINE_DISABLE_IRQ,
23 STOPMACHINE_EXIT,
24};
25
26static enum stopmachine_state stopmachine_state;
27static unsigned int stopmachine_num_threads;
28static atomic_t stopmachine_thread_ack;
29static DECLARE_MUTEX(stopmachine_mutex);
30
31static int stopmachine(void *cpu)
32{
33 int irqs_disabled = 0;
34 int prepared = 0;
35
36 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
37
38 /* Ack: we are alive */
39 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
40 atomic_inc(&stopmachine_thread_ack);
41
42 /* Simple state machine */
43 while (stopmachine_state != STOPMACHINE_EXIT) {
44 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
45 && !irqs_disabled) {
46 local_irq_disable();
47 irqs_disabled = 1;
48 /* Ack: irqs disabled. */
49 smp_mb(); /* Must read state first. */
50 atomic_inc(&stopmachine_thread_ack);
51 } else if (stopmachine_state == STOPMACHINE_PREPARE
52 && !prepared) {
53 /* Everyone is in place, hold CPU. */
54 preempt_disable();
55 prepared = 1;
56 smp_mb(); /* Must read state first. */
57 atomic_inc(&stopmachine_thread_ack);
58 }
59 /* Yield in first stage: migration threads need to
60 * help our sisters onto their CPUs. */
61 if (!prepared && !irqs_disabled)
62 yield();
63 else
64 cpu_relax();
65 }
66
67 /* Ack: we are exiting. */
68 smp_mb(); /* Must read state first. */
69 atomic_inc(&stopmachine_thread_ack);
70
71 if (irqs_disabled)
72 local_irq_enable();
73 if (prepared)
74 preempt_enable();
75
76 return 0;
77}
78
79/* Change the thread state */
80static void stopmachine_set_state(enum stopmachine_state state)
81{
82 atomic_set(&stopmachine_thread_ack, 0);
83 smp_wmb();
84 stopmachine_state = state;
85 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
86 cpu_relax();
87}
88
89static int stop_machine(void)
90{
91 int i, ret = 0;
92 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
93
94 /* One high-prio thread per cpu. We'll do this one. */
95 sched_setscheduler(current, SCHED_FIFO, &param);
96
97 atomic_set(&stopmachine_thread_ack, 0);
98 stopmachine_num_threads = 0;
99 stopmachine_state = STOPMACHINE_WAIT;
100
101 for_each_online_cpu(i) {
102 if (i == raw_smp_processor_id())
103 continue;
104 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
105 if (ret < 0)
106 break;
107 stopmachine_num_threads++;
108 }
109
110 /* Wait for them all to come to life. */
111 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
112 yield();
113
114 /* If some failed, kill them all. */
115 if (ret < 0) {
116 stopmachine_set_state(STOPMACHINE_EXIT);
117 return ret;
118 }
119
120 /* Now they are all started, make them hold the CPUs, ready. */
121 preempt_disable();
122 stopmachine_set_state(STOPMACHINE_PREPARE);
123
124 /* Make them disable irqs. */
125 local_irq_disable();
126 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
127
128 return 0;
129}
130
131static void restart_machine(void)
132{
133 stopmachine_set_state(STOPMACHINE_EXIT);
134 local_irq_enable();
135 preempt_enable_no_resched();
136}
137
138struct stop_machine_data
139{
140 int (*fn)(void *);
141 void *data;
142 struct completion done;
143};
144
145static int do_stop(void *_smdata)
146{
147 struct stop_machine_data *smdata = _smdata;
148 int ret;
149
150 ret = stop_machine();
151 if (ret == 0) {
152 ret = smdata->fn(smdata->data);
153 restart_machine();
154 }
155
156 /* We're done: you can kthread_stop us now */
157 complete(&smdata->done);
158
159 /* Wait for kthread_stop */
160 set_current_state(TASK_INTERRUPTIBLE);
161 while (!kthread_should_stop()) {
162 schedule();
163 set_current_state(TASK_INTERRUPTIBLE);
164 }
165 __set_current_state(TASK_RUNNING);
166 return ret;
167}
168
169struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
170 unsigned int cpu)
171{
172 struct stop_machine_data smdata;
173 struct task_struct *p;
174
175 smdata.fn = fn;
176 smdata.data = data;
177 init_completion(&smdata.done);
178
179 down(&stopmachine_mutex);
180
181 /* If they don't care which CPU fn runs on, bind to any online one. */
182 if (cpu == NR_CPUS)
183 cpu = raw_smp_processor_id();
184
185 p = kthread_create(do_stop, &smdata, "kstopmachine");
186 if (!IS_ERR(p)) {
187 kthread_bind(p, cpu);
188 wake_up_process(p);
189 wait_for_completion(&smdata.done);
190 }
191 up(&stopmachine_mutex);
192 return p;
193}
194
195int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
196{
197 struct task_struct *p;
198 int ret;
199
200 /* No CPUs can come up or down during this. */
201 lock_cpu_hotplug();
202 p = __stop_machine_run(fn, data, cpu);
203 if (!IS_ERR(p))
204 ret = kthread_stop(p);
205 else
206 ret = PTR_ERR(p);
207 unlock_cpu_hotplug();
208
209 return ret;
210}