projects/linux·blob v2.6.15-rc4 · refs

212 lines · 4.8 KiB

1#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
28static int stopmachine(void *cpu)
29{
30 int irqs_disabled = 0;
31 int prepared = 0;
32
33 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
34
35 /* Ack: we are alive */
36 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
37 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. */
46 smp_mb(); /* Must read state first. */
47 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;
53 smp_mb(); /* Must read state first. */
54 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. */
65 smp_mb(); /* Must read state first. */
66 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);
80 smp_wmb();
81 stopmachine_state = state;
82 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
83 cpu_relax();
84}
85
86static int stop_machine(void)
87{
88 int i, ret = 0;
89 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
90 mm_segment_t old_fs = get_fs();
91
92 /* One high-prio thread per cpu. We'll do this one. */
93 set_fs(KERNEL_DS);
94 sys_sched_setscheduler(current->pid, SCHED_FIFO,
95 (struct sched_param __user *)&param);
96 set_fs(old_fs);
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 up(&stopmachine_mutex);
119 return ret;
120 }
121
122 /* Now they are all started, make them hold the CPUs, ready. */
123 preempt_disable();
124 stopmachine_set_state(STOPMACHINE_PREPARE);
125
126 /* Make them disable irqs. */
127 local_irq_disable();
128 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
129
130 return 0;
131}
132
133static void restart_machine(void)
134{
135 stopmachine_set_state(STOPMACHINE_EXIT);
136 local_irq_enable();
137 preempt_enable_no_resched();
138}
139
140struct stop_machine_data
141{
142 int (*fn)(void *);
143 void *data;
144 struct completion done;
145};
146
147static int do_stop(void *_smdata)
148{
149 struct stop_machine_data *smdata = _smdata;
150 int ret;
151
152 ret = stop_machine();
153 if (ret == 0) {
154 ret = smdata->fn(smdata->data);
155 restart_machine();
156 }
157
158 /* We're done: you can kthread_stop us now */
159 complete(&smdata->done);
160
161 /* Wait for kthread_stop */
162 set_current_state(TASK_INTERRUPTIBLE);
163 while (!kthread_should_stop()) {
164 schedule();
165 set_current_state(TASK_INTERRUPTIBLE);
166 }
167 __set_current_state(TASK_RUNNING);
168 return ret;
169}
170
171struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
172 unsigned int cpu)
173{
174 struct stop_machine_data smdata;
175 struct task_struct *p;
176
177 smdata.fn = fn;
178 smdata.data = data;
179 init_completion(&smdata.done);
180
181 down(&stopmachine_mutex);
182
183 /* If they don't care which CPU fn runs on, bind to any online one. */
184 if (cpu == NR_CPUS)
185 cpu = raw_smp_processor_id();
186
187 p = kthread_create(do_stop, &smdata, "kstopmachine");
188 if (!IS_ERR(p)) {
189 kthread_bind(p, cpu);
190 wake_up_process(p);
191 wait_for_completion(&smdata.done);
192 }
193 up(&stopmachine_mutex);
194 return p;
195}
196
197int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
198{
199 struct task_struct *p;
200 int ret;
201
202 /* No CPUs can come up or down during this. */
203 lock_cpu_hotplug();
204 p = __stop_machine_run(fn, data, cpu);
205 if (!IS_ERR(p))
206 ret = kthread_stop(p);
207 else
208 ret = PTR_ERR(p);
209 unlock_cpu_hotplug();
210
211 return ret;
212}