ia64/linux-2.6.18-xen.hg

view kernel/stop_machine.c @ 562:66faefe721eb

pvSCSI backend driver

Signed-off-by: Tomonari Horikoshi <t.horikoshi@jp.fujitsu.com>
Signed-off-by: Jun Kamada <kama@jp.fujitsu.com>
author Keir Fraser <keir.fraser@citrix.com>
date Mon Jun 02 09:58:27 2008 +0100 (2008-06-02)
parents 831230e53067
children
line source
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>
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. */
15 /* Thread to stop each CPU in user context. */
16 enum stopmachine_state {
17 STOPMACHINE_WAIT,
18 STOPMACHINE_PREPARE,
19 STOPMACHINE_DISABLE_IRQ,
20 STOPMACHINE_EXIT,
21 };
23 static enum stopmachine_state stopmachine_state;
24 static unsigned int stopmachine_num_threads;
25 static atomic_t stopmachine_thread_ack;
26 static DECLARE_MUTEX(stopmachine_mutex);
28 static int stopmachine(void *cpu)
29 {
30 int irqs_disabled = 0;
31 int prepared = 0;
33 set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
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);
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 }
64 /* Ack: we are exiting. */
65 smp_mb(); /* Must read state first. */
66 atomic_inc(&stopmachine_thread_ack);
68 if (irqs_disabled)
69 local_irq_enable();
70 if (prepared)
71 preempt_enable();
73 return 0;
74 }
76 /* Change the thread state */
77 static 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 }
86 static int stop_machine(void)
87 {
88 int i, ret = 0;
89 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
91 /* One high-prio thread per cpu. We'll do this one. */
92 sched_setscheduler(current, SCHED_FIFO, &param);
94 atomic_set(&stopmachine_thread_ack, 0);
95 stopmachine_num_threads = 0;
96 stopmachine_state = STOPMACHINE_WAIT;
98 for_each_online_cpu(i) {
99 if (i == raw_smp_processor_id())
100 continue;
101 ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
102 if (ret < 0)
103 break;
104 stopmachine_num_threads++;
105 }
107 /* Wait for them all to come to life. */
108 while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
109 yield();
111 /* If some failed, kill them all. */
112 if (ret < 0) {
113 stopmachine_set_state(STOPMACHINE_EXIT);
114 return ret;
115 }
117 /* Now they are all started, make them hold the CPUs, ready. */
118 preempt_disable();
119 stopmachine_set_state(STOPMACHINE_PREPARE);
121 /* Make them disable irqs. */
122 local_irq_disable();
123 stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
125 return 0;
126 }
128 static void restart_machine(void)
129 {
130 stopmachine_set_state(STOPMACHINE_EXIT);
131 local_irq_enable();
132 preempt_enable_no_resched();
133 }
135 struct stop_machine_data
136 {
137 int (*fn)(void *);
138 void *data;
139 struct completion done;
140 };
142 static int do_stop(void *_smdata)
143 {
144 struct stop_machine_data *smdata = _smdata;
145 int ret;
147 ret = stop_machine();
148 if (ret == 0) {
149 ret = smdata->fn(smdata->data);
150 restart_machine();
151 }
153 /* We're done: you can kthread_stop us now */
154 complete(&smdata->done);
156 /* Wait for kthread_stop */
157 set_current_state(TASK_INTERRUPTIBLE);
158 while (!kthread_should_stop()) {
159 schedule();
160 set_current_state(TASK_INTERRUPTIBLE);
161 }
162 __set_current_state(TASK_RUNNING);
163 return ret;
164 }
166 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
167 unsigned int cpu)
168 {
169 struct stop_machine_data smdata;
170 struct task_struct *p;
172 smdata.fn = fn;
173 smdata.data = data;
174 init_completion(&smdata.done);
176 down(&stopmachine_mutex);
178 /* If they don't care which CPU fn runs on, bind to any online one. */
179 if (cpu == NR_CPUS)
180 cpu = raw_smp_processor_id();
182 p = kthread_create(do_stop, &smdata, "kstopmachine");
183 if (!IS_ERR(p)) {
184 kthread_bind(p, cpu);
185 wake_up_process(p);
186 wait_for_completion(&smdata.done);
187 }
188 up(&stopmachine_mutex);
189 return p;
190 }
192 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
193 {
194 struct task_struct *p;
195 int ret;
197 /* No CPUs can come up or down during this. */
198 lock_cpu_hotplug();
199 p = __stop_machine_run(fn, data, cpu);
200 if (!IS_ERR(p))
201 ret = kthread_stop(p);
202 else
203 ret = PTR_ERR(p);
204 unlock_cpu_hotplug();
206 return ret;
207 }