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 #define KTHREAD_NICE_LEVEL (-5)
  20
  21 static DEFINE_SPINLOCK(kthread_create_lock);
  22 static LIST_HEAD(kthread_create_list);
  23 struct task_struct *kthreadd_task;
  24
  25 struct kthread_create_info
  26 {
  27         /* Information passed to kthread() from kthreadd. */
  28         int (*threadfn)(void *data);
  29         void *data;
  30
  31         /* Result passed back to kthread_create() from kthreadd. */
  32         struct task_struct *result;
  33         struct completion done;
  34
  35         struct list_head list;
  36 };
  37
  38 struct kthread {
  39         int should_stop;
  40         struct completion exited;
  41 };
  42
  43 #define to_kthread(tsk) \
  44         container_of((tsk)->vfork_done, struct kthread, exited)
  45
  46 /**
  47  * kthread_should_stop - should this kthread return now?
  48  *
  49  * When someone calls kthread_stop() on your kthread, it will be woken
  50  * and this will return true.  You should then return, and your return
  51  * value will be passed through to kthread_stop().
  52  */
  53 int kthread_should_stop(void)
  54 {
  55         return to_kthread(current)->should_stop;
  56 }
  57 EXPORT_SYMBOL(kthread_should_stop);
  58
  59 static int kthread(void *_create)
  60 {
  61         /* Copy data: it's on kthread's stack */
  62         struct kthread_create_info *create = _create;
  63         int (*threadfn)(void *data) = create->threadfn;
  64         void *data = create->data;
  65         struct kthread self;
  66         int ret;
  67
  68         self.should_stop = 0;
  69         init_completion(&self.exited);
  70         current->vfork_done = &self.exited;
  71
  72         /* OK, tell user we're spawned, wait for stop or wakeup */
  73         __set_current_state(TASK_UNINTERRUPTIBLE);
  74         create->result = current;
  75         complete(&create->done);
  76         schedule();
  77
  78         ret = -EINTR;
  79         if (!self.should_stop)
  80                 ret = threadfn(data);
  81
  82         /* we can't just return, we must preserve "self" on stack */
  83         do_exit(ret);
  84 }
  85
  86 static void create_kthread(struct kthread_create_info *create)
  87 {
  88         int pid;
  89
  90         /* We want our own signal handler (we take no signals by default). */
  91         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  92         if (pid < 0) {
  93                 create->result = ERR_PTR(pid);
  94                 complete(&create->done);
  95         }
  96 }
  97
  98 /**
  99  * kthread_create - create a kthread.
 100  * @threadfn: the function to run until signal_pending(current).
 101  * @data: data ptr for @threadfn.
 102  * @namefmt: printf-style name for the thread.
 103  *
 104  * Description: This helper function creates and names a kernel
 105  * thread.  The thread will be stopped: use wake_up_process() to start
 106  * it.  See also kthread_run(), kthread_create_on_cpu().
 107  *
 108  * When woken, the thread will run @threadfn() with @data as its
 109  * argument. @threadfn() can either call do_exit() directly if it is a
 110  * standalone thread for which noone will call kthread_stop(), or
 111  * return when 'kthread_should_stop()' is true (which means
 112  * kthread_stop() has been called).  The return value should be zero
 113  * or a negative error number; it will be passed to kthread_stop().
 114  *
 115  * Returns a task_struct or ERR_PTR(-ENOMEM).
 116  */
 117 struct task_struct *kthread_create(int (*threadfn)(void *data),
 118                                    void *data,
 119                                    const char namefmt[],
 120                                    ...)
 121 {
 122         struct kthread_create_info create;
 123
 124         create.threadfn = threadfn;
 125         create.data = data;
 126         init_completion(&create.done);
 127
 128         spin_lock(&kthread_create_lock);
 129         list_add_tail(&create.list, &kthread_create_list);
 130         spin_unlock(&kthread_create_lock);
 131
 132         wake_up_process(kthreadd_task);
 133         wait_for_completion(&create.done);
 134
 135         if (!IS_ERR(create.result)) {
 136                 struct sched_param param = { .sched_priority = 0 };
 137                 va_list args;
 138
 139                 va_start(args, namefmt);
 140                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 141                           namefmt, args);
 142                 va_end(args);
 143                 /*
 144                  * root may have changed our (kthreadd's) priority or CPU mask.
 145                  * The kernel thread should not inherit these properties.
 146                  */
 147                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 148                 set_user_nice(create.result, KTHREAD_NICE_LEVEL);
 149                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 150         }
 151         return create.result;
 152 }
 153 EXPORT_SYMBOL(kthread_create);
 154
 155 /**
 156  * kthread_bind - bind a just-created kthread to a cpu.
 157  * @k: thread created by kthread_create().
 158  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 159  *
 160  * Description: This function is equivalent to set_cpus_allowed(),
 161  * except that @cpu doesn't need to be online, and the thread must be
 162  * stopped (i.e., just returned from kthread_create()).
 163  */
 164 void kthread_bind(struct task_struct *k, unsigned int cpu)
 165 {
 166         /* Must have done schedule() in kthread() before we set_task_cpu */
 167         if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
 168                 WARN_ON(1);
 169                 return;
 170         }
 171         set_task_cpu(k, cpu);
 172         k->cpus_allowed = cpumask_of_cpu(cpu);
 173         k->rt.nr_cpus_allowed = 1;
 174         k->flags |= PF_THREAD_BOUND;
 175 }
 176 EXPORT_SYMBOL(kthread_bind);
 177
 178 /**
 179  * kthread_stop - stop a thread created by kthread_create().
 180  * @k: thread created by kthread_create().
 181  *
 182  * Sets kthread_should_stop() for @k to return true, wakes it, and
 183  * waits for it to exit. This can also be called after kthread_create()
 184  * instead of calling wake_up_process(): the thread will exit without
 185  * calling threadfn().
 186  *
 187  * If threadfn() may call do_exit() itself, the caller must ensure
 188  * task_struct can't go away.
 189  *
 190  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 191  * was never called.
 192  */
 193 int kthread_stop(struct task_struct *k)
 194 {
 195         struct kthread *kthread;
 196         int ret;
 197
 198         trace_sched_kthread_stop(k);
 199         get_task_struct(k);
 200
 201         kthread = to_kthread(k);
 202         barrier(); /* it might have exited */
 203         if (k->vfork_done != NULL) {
 204                 kthread->should_stop = 1;
 205                 wake_up_process(k);
 206                 wait_for_completion(&kthread->exited);
 207         }
 208         ret = k->exit_code;
 209
 210         put_task_struct(k);
 211         trace_sched_kthread_stop_ret(ret);
 212
 213         return ret;
 214 }
 215 EXPORT_SYMBOL(kthread_stop);
 216
 217 int kthreadd(void *unused)
 218 {
 219         struct task_struct *tsk = current;
 220
 221         /* Setup a clean context for our children to inherit. */
 222         set_task_comm(tsk, "kthreadd");
 223         ignore_signals(tsk);
 224         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 225         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 226         set_mems_allowed(node_possible_map);
 227
 228         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 229
 230         for (;;) {
 231                 set_current_state(TASK_INTERRUPTIBLE);
 232                 if (list_empty(&kthread_create_list))
 233                         schedule();
 234                 __set_current_state(TASK_RUNNING);
 235
 236                 spin_lock(&kthread_create_lock);
 237                 while (!list_empty(&kthread_create_list)) {
 238                         struct kthread_create_info *create;
 239
 240                         create = list_entry(kthread_create_list.next,
 241                                             struct kthread_create_info, list);
 242                         list_del_init(&create->list);
 243                         spin_unlock(&kthread_create_lock);
 244
 245                         create_kthread(create);
 246
 247                         spin_lock(&kthread_create_lock);
 248                 }
 249                 spin_unlock(&kthread_create_lock);
 250         }
 251
 252         return 0;
 253 }