xref: /openbmc/linux/kernel/stop_machine.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 static DECLARE_MUTEX(stopmachine_mutex);
33 
34 static int stopmachine(void *cpu)
35 {
36 	int irqs_disabled = 0;
37 	int prepared = 0;
38 
39 	set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
40 
41 	/* Ack: we are alive */
42 	smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
43 	atomic_inc(&stopmachine_thread_ack);
44 
45 	/* Simple state machine */
46 	while (stopmachine_state != STOPMACHINE_EXIT) {
47 		if (stopmachine_state == STOPMACHINE_DISABLE_IRQ
48 		    && !irqs_disabled) {
49 			local_irq_disable();
50 			hard_irq_disable();
51 			irqs_disabled = 1;
52 			/* Ack: irqs disabled. */
53 			smp_mb(); /* Must read state first. */
54 			atomic_inc(&stopmachine_thread_ack);
55 		} else if (stopmachine_state == STOPMACHINE_PREPARE
56 			   && !prepared) {
57 			/* Everyone is in place, hold CPU. */
58 			preempt_disable();
59 			prepared = 1;
60 			smp_mb(); /* Must read state first. */
61 			atomic_inc(&stopmachine_thread_ack);
62 		}
63 		/* Yield in first stage: migration threads need to
64 		 * help our sisters onto their CPUs. */
65 		if (!prepared && !irqs_disabled)
66 			yield();
67 		else
68 			cpu_relax();
69 	}
70 
71 	/* Ack: we are exiting. */
72 	smp_mb(); /* Must read state first. */
73 	atomic_inc(&stopmachine_thread_ack);
74 
75 	if (irqs_disabled)
76 		local_irq_enable();
77 	if (prepared)
78 		preempt_enable();
79 
80 	return 0;
81 }
82 
83 /* Change the thread state */
84 static void stopmachine_set_state(enum stopmachine_state state)
85 {
86 	atomic_set(&stopmachine_thread_ack, 0);
87 	smp_wmb();
88 	stopmachine_state = state;
89 	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
90 		cpu_relax();
91 }
92 
93 static int stop_machine(void)
94 {
95 	int i, ret = 0;
96 	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
97 
98 	/* One high-prio thread per cpu.  We'll do this one. */
99 	sched_setscheduler(current, SCHED_FIFO, &param);
100 
101 	atomic_set(&stopmachine_thread_ack, 0);
102 	stopmachine_num_threads = 0;
103 	stopmachine_state = STOPMACHINE_WAIT;
104 
105 	for_each_online_cpu(i) {
106 		if (i == raw_smp_processor_id())
107 			continue;
108 		ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
109 		if (ret < 0)
110 			break;
111 		stopmachine_num_threads++;
112 	}
113 
114 	/* Wait for them all to come to life. */
115 	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
116 		yield();
117 
118 	/* If some failed, kill them all. */
119 	if (ret < 0) {
120 		stopmachine_set_state(STOPMACHINE_EXIT);
121 		return ret;
122 	}
123 
124 	/* Now they are all started, make them hold the CPUs, ready. */
125 	preempt_disable();
126 	stopmachine_set_state(STOPMACHINE_PREPARE);
127 
128 	/* Make them disable irqs. */
129 	local_irq_disable();
130 	hard_irq_disable();
131 	stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
132 
133 	return 0;
134 }
135 
136 static void restart_machine(void)
137 {
138 	stopmachine_set_state(STOPMACHINE_EXIT);
139 	local_irq_enable();
140 	preempt_enable_no_resched();
141 }
142 
143 struct stop_machine_data
144 {
145 	int (*fn)(void *);
146 	void *data;
147 	struct completion done;
148 };
149 
150 static int do_stop(void *_smdata)
151 {
152 	struct stop_machine_data *smdata = _smdata;
153 	int ret;
154 
155 	ret = stop_machine();
156 	if (ret == 0) {
157 		ret = smdata->fn(smdata->data);
158 		restart_machine();
159 	}
160 
161 	/* We're done: you can kthread_stop us now */
162 	complete(&smdata->done);
163 
164 	/* Wait for kthread_stop */
165 	set_current_state(TASK_INTERRUPTIBLE);
166 	while (!kthread_should_stop()) {
167 		schedule();
168 		set_current_state(TASK_INTERRUPTIBLE);
169 	}
170 	__set_current_state(TASK_RUNNING);
171 	return ret;
172 }
173 
174 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
175 				       unsigned int cpu)
176 {
177 	struct stop_machine_data smdata;
178 	struct task_struct *p;
179 
180 	smdata.fn = fn;
181 	smdata.data = data;
182 	init_completion(&smdata.done);
183 
184 	down(&stopmachine_mutex);
185 
186 	/* If they don't care which CPU fn runs on, bind to any online one. */
187 	if (cpu == NR_CPUS)
188 		cpu = raw_smp_processor_id();
189 
190 	p = kthread_create(do_stop, &smdata, "kstopmachine");
191 	if (!IS_ERR(p)) {
192 		kthread_bind(p, cpu);
193 		wake_up_process(p);
194 		wait_for_completion(&smdata.done);
195 	}
196 	up(&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 	lock_cpu_hotplug();
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 	unlock_cpu_hotplug();
213 
214 	return ret;
215 }
216 EXPORT_SYMBOL_GPL(stop_machine_run);
217