kernel/kthread.c

   1 /* Kernel thread helper functions.
   2  *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
   3  *
   4  * Creation is done via kthreadd, so that we get a clean environment
   5  * even if we're invoked from userspace (think modprobe, hotplug cpu,
   6  * etc.).
   7  */
   8 #include <linux/sched.h>
   9 #include <linux/kthread.h>
  10 #include <linux/completion.h>
  11 #include <linux/err.h>
  12 #include <linux/cpuset.h>
  13 #include <linux/unistd.h>
  14 #include <linux/file.h>
  15 #include <linux/module.h>
  16 #include <linux/mutex.h>
  17 #include <trace/events/sched.h>
  18
  19 static DEFINE_SPINLOCK(kthread_create_lock);
  20 static LIST_HEAD(kthread_create_list);
  21 struct task_struct *kthreadd_task;
  22
  23 struct kthread_create_info
  24 {
  25         /* Information passed to kthread() from kthreadd. */
  26         int (*threadfn)(void *data);
  27         void *data;
  28
  29         /* Result passed back to kthread_create() from kthreadd. */
  30         struct task_struct *result;
  31         struct completion done;
  32
  33         struct list_head list;
  34 };
  35
  36 struct kthread {
  37         int should_stop;
  38         struct completion exited;
  39 };
  40
  41 #define to_kthread(tsk) \
  42         container_of((tsk)->vfork_done, struct kthread, exited)
  43
  44 /**
  45  * kthread_should_stop - should this kthread return now?
  46  *
  47  * When someone calls kthread_stop() on your kthread, it will be woken
  48  * and this will return true.  You should then return, and your return
  49  * value will be passed through to kthread_stop().
  50  */
  51 int kthread_should_stop(void)
  52 {
  53         return to_kthread(current)->should_stop;
  54 }
  55 EXPORT_SYMBOL(kthread_should_stop);
  56
  57 static int kthread(void *_create)
  58 {
  59         /* Copy data: it's on kthread's stack */
  60         struct kthread_create_info *create = _create;
  61         int (*threadfn)(void *data) = create->threadfn;
  62         void *data = create->data;
  63         struct kthread self;
  64         int ret;
  65
  66         self.should_stop = 0;
  67         init_completion(&self.exited);
  68         current->vfork_done = &self.exited;
  69
  70         /* OK, tell user we're spawned, wait for stop or wakeup */
  71         __set_current_state(TASK_UNINTERRUPTIBLE);
  72         create->result = current;
  73         complete(&create->done);
  74         schedule();
  75
  76         ret = -EINTR;
  77         if (!self.should_stop)
  78                 ret = threadfn(data);
  79
  80         /* we can't just return, we must preserve "self" on stack */
  81         do_exit(ret);
  82 }
  83
  84 static void create_kthread(struct kthread_create_info *create)
  85 {
  86         int pid;
  87
  88         /* We want our own signal handler (we take no signals by default). */
  89         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  90         if (pid < 0) {
  91                 create->result = ERR_PTR(pid);
  92                 complete(&create->done);
  93         }
  94 }
  95
  96 /**
  97  * kthread_create - create a kthread.
  98  * @threadfn: the function to run until signal_pending(current).
  99  * @data: data ptr for @threadfn.
 100  * @namefmt: printf-style name for the thread.
 101  *
 102  * Description: This helper function creates and names a kernel
 103  * thread.  The thread will be stopped: use wake_up_process() to start
 104  * it.  See also kthread_run(), kthread_create_on_cpu().
 105  *
 106  * When woken, the thread will run @threadfn() with @data as its
 107  * argument. @threadfn() can either call do_exit() directly if it is a
 108  * standalone thread for which noone will call kthread_stop(), or
 109  * return when 'kthread_should_stop()' is true (which means
 110  * kthread_stop() has been called).  The return value should be zero
 111  * or a negative error number; it will be passed to kthread_stop().
 112  *
 113  * Returns a task_struct or ERR_PTR(-ENOMEM).
 114  */
 115 struct task_struct *kthread_create(int (*threadfn)(void *data),
 116                                    void *data,
 117                                    const char namefmt[],
 118                                    ...)
 119 {
 120         struct kthread_create_info create;
 121
 122         create.threadfn = threadfn;
 123         create.data = data;
 124         init_completion(&create.done);
 125
 126         spin_lock(&kthread_create_lock);
 127         list_add_tail(&create.list, &kthread_create_list);
 128         spin_unlock(&kthread_create_lock);
 129
 130         wake_up_process(kthreadd_task);
 131         wait_for_completion(&create.done);
 132
 133         if (!IS_ERR(create.result)) {
 134                 struct sched_param param = { .sched_priority = 0 };
 135                 va_list args;
 136
 137                 va_start(args, namefmt);
 138                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 139                           namefmt, args);
 140                 va_end(args);
 141                 /*
 142                  * root may have changed our (kthreadd's) priority or CPU mask.
 143                  * The kernel thread should not inherit these properties.
 144                  */
 145                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 146                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 147         }
 148         return create.result;
 149 }
 150 EXPORT_SYMBOL(kthread_create);
 151
 152 /**
 153  * kthread_bind - bind a just-created kthread to a cpu.
 154  * @p: thread created by kthread_create().
 155  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 156  *
 157  * Description: This function is equivalent to set_cpus_allowed(),
 158  * except that @cpu doesn't need to be online, and the thread must be
 159  * stopped (i.e., just returned from kthread_create()).
 160  */
 161 void kthread_bind(struct task_struct *p, unsigned int cpu)
 162 {
 163         /* Must have done schedule() in kthread() before we set_task_cpu */
 164         if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 165                 WARN_ON(1);
 166                 return;
 167         }
 168
 169         p->cpus_allowed = cpumask_of_cpu(cpu);
 170         p->rt.nr_cpus_allowed = 1;
 171         p->flags |= PF_THREAD_BOUND;
 172 }
 173 EXPORT_SYMBOL(kthread_bind);
 174
 175 /**
 176  * kthread_stop - stop a thread created by kthread_create().
 177  * @k: thread created by kthread_create().
 178  *
 179  * Sets kthread_should_stop() for @k to return true, wakes it, and
 180  * waits for it to exit. This can also be called after kthread_create()
 181  * instead of calling wake_up_process(): the thread will exit without
 182  * calling threadfn().
 183  *
 184  * If threadfn() may call do_exit() itself, the caller must ensure
 185  * task_struct can't go away.
 186  *
 187  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 188  * was never called.
 189  */
 190 int kthread_stop(struct task_struct *k)
 191 {
 192         struct kthread *kthread;
 193         int ret;
 194
 195         trace_sched_kthread_stop(k);
 196         get_task_struct(k);
 197
 198         kthread = to_kthread(k);
 199         barrier(); /* it might have exited */
 200         if (k->vfork_done != NULL) {
 201                 kthread->should_stop = 1;
 202                 wake_up_process(k);
 203                 wait_for_completion(&kthread->exited);
 204         }
 205         ret = k->exit_code;
 206
 207         put_task_struct(k);
 208         trace_sched_kthread_stop_ret(ret);
 209
 210         return ret;
 211 }
 212 EXPORT_SYMBOL(kthread_stop);
 213
 214 int kthreadd(void *unused)
 215 {
 216         struct task_struct *tsk = current;
 217
 218         /* Setup a clean context for our children to inherit. */
 219         set_task_comm(tsk, "kthreadd");
 220         ignore_signals(tsk);
 221         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 222         set_mems_allowed(node_possible_map);
 223
 224         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 225
 226         for (;;) {
 227                 set_current_state(TASK_INTERRUPTIBLE);
 228                 if (list_empty(&kthread_create_list))
 229                         schedule();
 230                 __set_current_state(TASK_RUNNING);
 231
 232                 spin_lock(&kthread_create_lock);
 233                 while (!list_empty(&kthread_create_list)) {
 234                         struct kthread_create_info *create;
 235
 236                         create = list_entry(kthread_create_list.next,
 237                                             struct kthread_create_info, list);
 238                         list_del_init(&create->list);
 239                         spin_unlock(&kthread_create_lock);
 240
 241                         create_kthread(create);
 242
 243                         spin_lock(&kthread_create_lock);
 244                 }
 245                 spin_unlock(&kthread_create_lock);
 246         }
 247
 248         return 0;
 249 }