1 /* Copyright 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/semaphore.h>
15 #include <asm/uaccess.h>
16
17 /* Since we effect priority and affinity (both of which are visible
18 * to, and settable by outside processes) we do indirection via a
19 * kthread. */
20
21 /* Thread to stop each CPU in user context. */
22 enum stopmachine_state {
23 STOPMACHINE_WAIT,
24 STOPMACHINE_PREPARE,
25 STOPMACHINE_DISABLE_IRQ,
26 STOPMACHINE_EXIT,
27 };
28
29 static enum stopmachine_state stopmachine_state;
30 static unsigned int stopmachine_num_threads;
31 static atomic_t stopmachine_thread_ack;
32
33 static int stopmachine(void *cpu)
34 {
35 int irqs_disabled = 0;
36 int prepared = 0;
37
38 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
39
40 /* Ack: we are alive */
41 smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
42 atomic_inc(&stopmachine_thread_ack);
43
44 /* Simple state machine */
45 while (stopmachine_state != STOPMACHINE_EXIT) {
46 if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
47 && !irqs_disabled) {
48 local_irq_disable();
49 hard_irq_disable();
50 irqs_disabled = 1;
51 /* Ack: irqs disabled. */
52 smp_mb(); /* Must read state first. */
53 atomic_inc(&stopmachine_thread_ack);
54 } else if (stopmachine_state == STOPMACHINE_PREPARE
55 && !prepared) {
56 /* Everyone is in place, hold CPU. */
57 preempt_disable();
58 prepared = 1;
59 smp_mb(); /* Must read state first. */
60 atomic_inc(&stopmachine_thread_ack);
61 }
62 /* Yield in first stage: migration threads need to
63 * help our sisters onto their CPUs. */
64 if (!prepared && !irqs_disabled)
65 __yield();
66 else
67 cpu_relax();
68 }
69
70 /* Ack: we are exiting. */
71 smp_mb(); /* Must read state first. */
72 atomic_inc(&stopmachine_thread_ack);
73
74 if (irqs_disabled)
75 local_irq_enable();
76 if (prepared)
77 preempt_enable();
78
79 return 0;
80 }
81
82 /* Change the thread state */
83 static void stopmachine_set_state(enum stopmachine_state state)
84 {
85 atomic_set(&stopmachine_thread_ack, 0);
86 smp_wmb();
87 stopmachine_state = state;
88 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
89 cpu_relax();
90 }
91
92 static int stop_machine(void)
93 {
94 int i, ret = 0;
95
96 atomic_set(&stopmachine_thread_ack, 0);
97 stopmachine_num_threads = 0;
98 stopmachine_state = STOPMACHINE_WAIT;
99
100 for_each_online_cpu(i) {
101 if (i == raw_smp_processor_id())
102 continue;
103 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
104 if (ret < 0)
105 break;
106 stopmachine_num_threads++;
107 }
108
109 /* Wait for them all to come to life. */
110 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
111 __yield();
112
113 /* If some failed, kill them all. */
114 if (ret < 0) {
115 stopmachine_set_state(STOPMACHINE_EXIT);
116 return ret;
117 }
118
119 /* Now they are all started, make them hold the CPUs, ready. */
120 preempt_disable();
121 stopmachine_set_state(STOPMACHINE_PREPARE);
122
123 /* Make them disable irqs. */
124 local_irq_disable();
125 hard_irq_disable();
126 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
127
128 return 0;
129 }
130
131 static void restart_machine(void)
132 {
133 stopmachine_set_state(STOPMACHINE_EXIT);
134 local_irq_enable();
135 __preempt_enable_no_resched();
136 }
137
138 struct stop_machine_data
139 {
140 int (*fn)(void *);
141 void *data;
142 struct completion done;
143 };
144
145 static 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
169 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
170 unsigned int cpu)
171 {
172 static DEFINE_MUTEX(stopmachine_mutex);
173 struct stop_machine_data smdata;
174 struct task_struct *p;
175
176 smdata.fn = fn;
177 smdata.data = data;
178 init_completion(&smdata.done);
179
180 mutex_lock(&stopmachine_mutex);
181
182 /* If they don't care which CPU fn runs on, bind to any online one. */
183 if (cpu == NR_CPUS)
184 cpu = raw_smp_processor_id();
185
186 p = kthread_create(do_stop, &smdata, "kstopmachine");
187 if (!IS_ERR(p)) {
188 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
189
190 /* One high-prio thread per cpu. We'll do this one. */
191 sched_setscheduler(p, SCHED_FIFO, ¶m);
192 kthread_bind(p, cpu);
193 wake_up_process(p);
194 wait_for_completion(&smdata.done);
195 }
196 mutex_unlock(&stopmachine_mutex);
197 return p;
198 }
199
200 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
201 {
202 struct task_struct *p;
203 int ret;
204
205 /* No CPUs can come up or down during this. */
206 get_online_cpus();
207 p = __stop_machine_run(fn, data, cpu);
208 if (!IS_ERR(p))
209 ret = kthread_stop(p);
210 else
211 ret = PTR_ERR(p);
212 put_online_cpus();
213
214 return ret;
215 }
216 EXPORT_SYMBOL_GPL(stop_machine_run);
217
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