aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/cpu.c
blob: d61ba88f34e57b90edae90342ed1db59ebfbb59c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <asm/semaphore.h>

/* This protects CPUs going up and down... */
DECLARE_MUTEX(cpucontrol);
EXPORT_SYMBOL_GPL(cpucontrol);

static struct notifier_block *cpu_chain;

/*
 * Used to check by callers if they need to acquire the cpucontrol
 * or not to protect a cpu from being removed. Its sometimes required to
 * call these functions both for normal operations, and in response to
 * a cpu being added/removed. If the context of the call is in the same
 * thread context as a CPU hotplug thread, we dont need to take the lock
 * since its already protected
 * check drivers/cpufreq/cpufreq.c for its usage - Ashok Raj
 */

int current_in_cpu_hotplug(void)
{
	return (current->flags & PF_HOTPLUG_CPU);
}

EXPORT_SYMBOL_GPL(current_in_cpu_hotplug);


/* Need to know about CPUs going up/down? */
int register_cpu_notifier(struct notifier_block *nb)
{
	int ret;

	if ((ret = down_interruptible(&cpucontrol)) != 0)
		return ret;
	ret = notifier_chain_register(&cpu_chain, nb);
	up(&cpucontrol);
	return ret;
}
EXPORT_SYMBOL(register_cpu_notifier);

void unregister_cpu_notifier(struct notifier_block *nb)
{
	down(&cpucontrol);
	notifier_chain_unregister(&cpu_chain, nb);
	up(&cpucontrol);
}
EXPORT_SYMBOL(unregister_cpu_notifier);

#ifdef CONFIG_HOTPLUG_CPU
static inline void check_for_tasks(int cpu)
{
	struct task_struct *p;

	write_lock_irq(&tasklist_lock);
	for_each_process(p) {
		if (task_cpu(p) == cpu &&
		    (!cputime_eq(p->utime, cputime_zero) ||
		     !cputime_eq(p->stime, cputime_zero)))
			printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
				(state = %ld, flags = %lx) \n",
				 p->comm, p->pid, cpu, p->state, p->flags);
	}
	write_unlock_irq(&tasklist_lock);
}

/* Take this CPU down. */
static int take_cpu_down(void *unused)
{
	int err;

	/* Ensure this CPU doesn't handle any more interrupts. */
	err = __cpu_disable();
	if (err < 0)
		return err;

	/* Force idle task to run as soon as we yield: it should
	   immediately notice cpu is offline and die quickly. */
	sched_idle_next();
	return 0;
}

int cpu_down(unsigned int cpu)
{
	int err;
	struct task_struct *p;
	cpumask_t old_allowed, tmp;

	if ((err = lock_cpu_hotplug_interruptible()) != 0)
		return err;

	if (num_online_cpus() == 1) {
		err = -EBUSY;
		goto out;
	}

	if (!cpu_online(cpu)) {
		err = -EINVAL;
		goto out;
	}

	/*
	 * Leave a trace in current->flags indicating we are already in
	 * process of performing CPU hotplug. Callers can check if cpucontrol
	 * is already acquired by current thread, and if so not cause
	 * a dead lock by not acquiring the lock
	 */
	current->flags |= PF_HOTPLUG_CPU;
	err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
						(void *)(long)cpu);
	if (err == NOTIFY_BAD) {
		printk("%s: attempt to take down CPU %u failed\n",
				__FUNCTION__, cpu);
		err = -EINVAL;
		goto out;
	}

	/* Ensure that we are not runnable on dying cpu */
	old_allowed = current->cpus_allowed;
	tmp = CPU_MASK_ALL;
	cpu_clear(cpu, tmp);
	set_cpus_allowed(current, tmp);

	p = __stop_machine_run(take_cpu_down, NULL, cpu);
	if (IS_ERR(p)) {
		/* CPU didn't die: tell everyone.  Can't complain. */
		if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
				(void *)(long)cpu) == NOTIFY_BAD)
			BUG();

		err = PTR_ERR(p);
		goto out_allowed;
	}

	if (cpu_online(cpu))
		goto out_thread;

	/* Wait for it to sleep (leaving idle task). */
	while (!idle_cpu(cpu))
		yield();

	/* This actually kills the CPU. */
	__cpu_die(cpu);

	/* Move it here so it can run. */
	kthread_bind(p, get_cpu());
	put_cpu();

	/* CPU is completely dead: tell everyone.  Too late to complain. */
	if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
	    == NOTIFY_BAD)
		BUG();

	check_for_tasks(cpu);

out_thread:
	err = kthread_stop(p);
out_allowed:
	set_cpus_allowed(current, old_allowed);
out:
	current->flags &= ~PF_HOTPLUG_CPU;
	unlock_cpu_hotplug();
	return err;
}
#endif /*CONFIG_HOTPLUG_CPU*/

int __devinit cpu_up(unsigned int cpu)
{
	int ret;
	void *hcpu = (void *)(long)cpu;

	if ((ret = down_interruptible(&cpucontrol)) != 0)
		return ret;

	if (cpu_online(cpu) || !cpu_present(cpu)) {
		ret = -EINVAL;
		goto out;
	}

	/*
	 * Leave a trace in current->flags indicating we are already in
	 * process of performing CPU hotplug.
	 */
	current->flags |= PF_HOTPLUG_CPU;
	ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
	if (ret == NOTIFY_BAD) {
		printk("%s: attempt to bring up CPU %u failed\n",
				__FUNCTION__, cpu);
		ret = -EINVAL;
		goto out_notify;
	}

	/* Arch-specific enabling code. */
	ret = __cpu_up(cpu);
	if (ret != 0)
		goto out_notify;
	if (!cpu_online(cpu))
		BUG();

	/* Now call notifier in preparation. */
	notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);

out_notify:
	if (ret != 0)
		notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
out:
	current->flags &= ~PF_HOTPLUG_CPU;
	up(&cpucontrol);
	return ret;
}