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TOMOYO Linux Cross Reference
Linux/kernel/smpboot.c

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  1 /*
  2  * Common SMP CPU bringup/teardown functions
  3  */
  4 #include <linux/cpu.h>
  5 #include <linux/err.h>
  6 #include <linux/smp.h>
  7 #include <linux/init.h>
  8 #include <linux/list.h>
  9 #include <linux/slab.h>
 10 #include <linux/sched.h>
 11 #include <linux/export.h>
 12 #include <linux/percpu.h>
 13 #include <linux/kthread.h>
 14 #include <linux/smpboot.h>
 15 
 16 #include "smpboot.h"
 17 
 18 #ifdef CONFIG_SMP
 19 
 20 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
 21 /*
 22  * For the hotplug case we keep the task structs around and reuse
 23  * them.
 24  */
 25 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
 26 
 27 struct task_struct *idle_thread_get(unsigned int cpu)
 28 {
 29         struct task_struct *tsk = per_cpu(idle_threads, cpu);
 30 
 31         if (!tsk)
 32                 return ERR_PTR(-ENOMEM);
 33         init_idle(tsk, cpu);
 34         return tsk;
 35 }
 36 
 37 void __init idle_thread_set_boot_cpu(void)
 38 {
 39         per_cpu(idle_threads, smp_processor_id()) = current;
 40 }
 41 
 42 /**
 43  * idle_init - Initialize the idle thread for a cpu
 44  * @cpu:        The cpu for which the idle thread should be initialized
 45  *
 46  * Creates the thread if it does not exist.
 47  */
 48 static inline void idle_init(unsigned int cpu)
 49 {
 50         struct task_struct *tsk = per_cpu(idle_threads, cpu);
 51 
 52         if (!tsk) {
 53                 tsk = fork_idle(cpu);
 54                 if (IS_ERR(tsk))
 55                         pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
 56                 else
 57                         per_cpu(idle_threads, cpu) = tsk;
 58         }
 59 }
 60 
 61 /**
 62  * idle_threads_init - Initialize idle threads for all cpus
 63  */
 64 void __init idle_threads_init(void)
 65 {
 66         unsigned int cpu, boot_cpu;
 67 
 68         boot_cpu = smp_processor_id();
 69 
 70         for_each_possible_cpu(cpu) {
 71                 if (cpu != boot_cpu)
 72                         idle_init(cpu);
 73         }
 74 }
 75 #endif
 76 
 77 #endif /* #ifdef CONFIG_SMP */
 78 
 79 static LIST_HEAD(hotplug_threads);
 80 static DEFINE_MUTEX(smpboot_threads_lock);
 81 
 82 struct smpboot_thread_data {
 83         unsigned int                    cpu;
 84         unsigned int                    status;
 85         struct smp_hotplug_thread       *ht;
 86 };
 87 
 88 enum {
 89         HP_THREAD_NONE = 0,
 90         HP_THREAD_ACTIVE,
 91         HP_THREAD_PARKED,
 92 };
 93 
 94 /**
 95  * smpboot_thread_fn - percpu hotplug thread loop function
 96  * @data:       thread data pointer
 97  *
 98  * Checks for thread stop and park conditions. Calls the necessary
 99  * setup, cleanup, park and unpark functions for the registered
100  * thread.
101  *
102  * Returns 1 when the thread should exit, 0 otherwise.
103  */
104 static int smpboot_thread_fn(void *data)
105 {
106         struct smpboot_thread_data *td = data;
107         struct smp_hotplug_thread *ht = td->ht;
108 
109         while (1) {
110                 set_current_state(TASK_INTERRUPTIBLE);
111                 preempt_disable();
112                 if (kthread_should_stop()) {
113                         set_current_state(TASK_RUNNING);
114                         preempt_enable();
115                         if (ht->cleanup)
116                                 ht->cleanup(td->cpu, cpu_online(td->cpu));
117                         kfree(td);
118                         return 0;
119                 }
120 
121                 if (kthread_should_park()) {
122                         __set_current_state(TASK_RUNNING);
123                         preempt_enable();
124                         if (ht->park && td->status == HP_THREAD_ACTIVE) {
125                                 BUG_ON(td->cpu != smp_processor_id());
126                                 ht->park(td->cpu);
127                                 td->status = HP_THREAD_PARKED;
128                         }
129                         kthread_parkme();
130                         /* We might have been woken for stop */
131                         continue;
132                 }
133 
134                 BUG_ON(td->cpu != smp_processor_id());
135 
136                 /* Check for state change setup */
137                 switch (td->status) {
138                 case HP_THREAD_NONE:
139                         preempt_enable();
140                         if (ht->setup)
141                                 ht->setup(td->cpu);
142                         td->status = HP_THREAD_ACTIVE;
143                         preempt_disable();
144                         break;
145                 case HP_THREAD_PARKED:
146                         preempt_enable();
147                         if (ht->unpark)
148                                 ht->unpark(td->cpu);
149                         td->status = HP_THREAD_ACTIVE;
150                         preempt_disable();
151                         break;
152                 }
153 
154                 if (!ht->thread_should_run(td->cpu)) {
155                         preempt_enable();
156                         schedule();
157                 } else {
158                         set_current_state(TASK_RUNNING);
159                         preempt_enable();
160                         ht->thread_fn(td->cpu);
161                 }
162         }
163 }
164 
165 static int
166 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
167 {
168         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
169         struct smpboot_thread_data *td;
170 
171         if (tsk)
172                 return 0;
173 
174         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
175         if (!td)
176                 return -ENOMEM;
177         td->cpu = cpu;
178         td->ht = ht;
179 
180         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
181                                     ht->thread_comm);
182         if (IS_ERR(tsk)) {
183                 kfree(td);
184                 return PTR_ERR(tsk);
185         }
186         get_task_struct(tsk);
187         *per_cpu_ptr(ht->store, cpu) = tsk;
188         if (ht->create) {
189                 /*
190                  * Make sure that the task has actually scheduled out
191                  * into park position, before calling the create
192                  * callback. At least the migration thread callback
193                  * requires that the task is off the runqueue.
194                  */
195                 if (!wait_task_inactive(tsk, TASK_PARKED))
196                         WARN_ON(1);
197                 else
198                         ht->create(cpu);
199         }
200         return 0;
201 }
202 
203 int smpboot_create_threads(unsigned int cpu)
204 {
205         struct smp_hotplug_thread *cur;
206         int ret = 0;
207 
208         mutex_lock(&smpboot_threads_lock);
209         list_for_each_entry(cur, &hotplug_threads, list) {
210                 ret = __smpboot_create_thread(cur, cpu);
211                 if (ret)
212                         break;
213         }
214         mutex_unlock(&smpboot_threads_lock);
215         return ret;
216 }
217 
218 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
219 {
220         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
221 
222         if (ht->pre_unpark)
223                 ht->pre_unpark(cpu);
224         kthread_unpark(tsk);
225 }
226 
227 void smpboot_unpark_threads(unsigned int cpu)
228 {
229         struct smp_hotplug_thread *cur;
230 
231         mutex_lock(&smpboot_threads_lock);
232         list_for_each_entry(cur, &hotplug_threads, list)
233                 smpboot_unpark_thread(cur, cpu);
234         mutex_unlock(&smpboot_threads_lock);
235 }
236 
237 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
238 {
239         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
240 
241         if (tsk && !ht->selfparking)
242                 kthread_park(tsk);
243 }
244 
245 void smpboot_park_threads(unsigned int cpu)
246 {
247         struct smp_hotplug_thread *cur;
248 
249         mutex_lock(&smpboot_threads_lock);
250         list_for_each_entry_reverse(cur, &hotplug_threads, list)
251                 smpboot_park_thread(cur, cpu);
252         mutex_unlock(&smpboot_threads_lock);
253 }
254 
255 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
256 {
257         unsigned int cpu;
258 
259         /* We need to destroy also the parked threads of offline cpus */
260         for_each_possible_cpu(cpu) {
261                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
262 
263                 if (tsk) {
264                         kthread_stop(tsk);
265                         put_task_struct(tsk);
266                         *per_cpu_ptr(ht->store, cpu) = NULL;
267                 }
268         }
269 }
270 
271 /**
272  * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
273  * @plug_thread:        Hotplug thread descriptor
274  *
275  * Creates and starts the threads on all online cpus.
276  */
277 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
278 {
279         unsigned int cpu;
280         int ret = 0;
281 
282         mutex_lock(&smpboot_threads_lock);
283         for_each_online_cpu(cpu) {
284                 ret = __smpboot_create_thread(plug_thread, cpu);
285                 if (ret) {
286                         smpboot_destroy_threads(plug_thread);
287                         goto out;
288                 }
289                 smpboot_unpark_thread(plug_thread, cpu);
290         }
291         list_add(&plug_thread->list, &hotplug_threads);
292 out:
293         mutex_unlock(&smpboot_threads_lock);
294         return ret;
295 }
296 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
297 
298 /**
299  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
300  * @plug_thread:        Hotplug thread descriptor
301  *
302  * Stops all threads on all possible cpus.
303  */
304 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
305 {
306         get_online_cpus();
307         mutex_lock(&smpboot_threads_lock);
308         list_del(&plug_thread->list);
309         smpboot_destroy_threads(plug_thread);
310         mutex_unlock(&smpboot_threads_lock);
311         put_online_cpus();
312 }
313 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
314 

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