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         struct completion started;
  31
  32         /* Result passed back to kthread_create() from kthreadd. */
  33         struct task_struct *result;
  34         struct completion done;
  35
  36         struct list_head list;
  37 };
  38
  39 struct kthread_stop_info
  40 {
  41         struct task_struct *k;
  42         int err;
  43         struct completion done;
  44 };
  45
  46 /* Thread stopping is done by setthing this var: lock serializes
  47  * multiple kthread_stop calls. */
  48 static DEFINE_MUTEX(kthread_stop_lock);
  49 static struct kthread_stop_info kthread_stop_info;
  50
  51 /**
  52  * kthread_should_stop - should this kthread return now?
  53  *
  54  * When someone calls kthread_stop() on your kthread, it will be woken
  55  * and this will return true.  You should then return, and your return
  56  * value will be passed through to kthread_stop().
  57  */
  58 int kthread_should_stop(void)
  59 {
  60         return (kthread_stop_info.k == current);
  61 }
  62 EXPORT_SYMBOL(kthread_should_stop);
  63
  64 static int kthread(void *_create)
  65 {
  66         struct kthread_create_info *create = _create;
  67         int (*threadfn)(void *data);
  68         void *data;
  69         int ret = -EINTR;
  70
  71         /* Copy data: it's on kthread's stack */
  72         threadfn = create->threadfn;
  73         data = create->data;
  74
  75         /* OK, tell user we're spawned, wait for stop or wakeup */
  76         __set_current_state(TASK_UNINTERRUPTIBLE);
  77         create->result = current;
  78         complete(&create->started);
  79         schedule();
  80
  81         if (!kthread_should_stop())
  82                 ret = threadfn(data);
  83
  84         /* It might have exited on its own, w/o kthread_stop.  Check. */
  85         if (kthread_should_stop()) {
  86                 kthread_stop_info.err = ret;
  87                 complete(&kthread_stop_info.done);
  88         }
  89         return 0;
  90 }
  91
  92 static void create_kthread(struct kthread_create_info *create)
  93 {
  94         int pid;
  95
  96         /* We want our own signal handler (we take no signals by default). */
  97         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  98         if (pid < 0)
  99                 create->result = ERR_PTR(pid);
 100         else
 101                 wait_for_completion(&create->started);
 102         complete(&create->done);
 103 }
 104
 105 /**
 106  * kthread_create - create a kthread.
 107  * @threadfn: the function to run until signal_pending(current).
 108  * @data: data ptr for @threadfn.
 109  * @namefmt: printf-style name for the thread.
 110  *
 111  * Description: This helper function creates and names a kernel
 112  * thread.  The thread will be stopped: use wake_up_process() to start
 113  * it.  See also kthread_run(), kthread_create_on_cpu().
 114  *
 115  * When woken, the thread will run @threadfn() with @data as its
 116  * argument. @threadfn() can either call do_exit() directly if it is a
 117  * standalone thread for which noone will call kthread_stop(), or
 118  * return when 'kthread_should_stop()' is true (which means
 119  * kthread_stop() has been called).  The return value should be zero
 120  * or a negative error number; it will be passed to kthread_stop().
 121  *
 122  * Returns a task_struct or ERR_PTR(-ENOMEM).
 123  */
 124 struct task_struct *kthread_create(int (*threadfn)(void *data),
 125                                    void *data,
 126                                    const char namefmt[],
 127                                    ...)
 128 {
 129         struct kthread_create_info create;
 130
 131         create.threadfn = threadfn;
 132         create.data = data;
 133         init_completion(&create.started);
 134         init_completion(&create.done);
 135
 136         spin_lock(&kthread_create_lock);
 137         list_add_tail(&create.list, &kthread_create_list);
 138         spin_unlock(&kthread_create_lock);
 139
 140         wake_up_process(kthreadd_task);
 141         wait_for_completion(&create.done);
 142
 143         if (!IS_ERR(create.result)) {
 144                 struct sched_param param = { .sched_priority = 0 };
 145                 va_list args;
 146
 147                 va_start(args, namefmt);
 148                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 149                           namefmt, args);
 150                 va_end(args);
 151                 /*
 152                  * root may have changed our (kthreadd's) priority or CPU mask.
 153                  * The kernel thread should not inherit these properties.
 154                  */
 155                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 156                 set_user_nice(create.result, KTHREAD_NICE_LEVEL);
 157                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 158         }
 159         return create.result;
 160 }
 161 EXPORT_SYMBOL(kthread_create);
 162
 163 /**
 164  * kthread_bind - bind a just-created kthread to a cpu.
 165  * @k: thread created by kthread_create().
 166  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 167  *
 168  * Description: This function is equivalent to set_cpus_allowed(),
 169  * except that @cpu doesn't need to be online, and the thread must be
 170  * stopped (i.e., just returned from kthread_create()).
 171  */
 172 void kthread_bind(struct task_struct *k, unsigned int cpu)
 173 {
 174         /* Must have done schedule() in kthread() before we set_task_cpu */
 175         if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
 176                 WARN_ON(1);
 177                 return;
 178         }
 179         set_task_cpu(k, cpu);
 180         k->cpus_allowed = cpumask_of_cpu(cpu);
 181         k->rt.nr_cpus_allowed = 1;
 182         k->flags |= PF_THREAD_BOUND;
 183 }
 184 EXPORT_SYMBOL(kthread_bind);
 185
 186 /**
 187  * kthread_stop - stop a thread created by kthread_create().
 188  * @k: thread created by kthread_create().
 189  *
 190  * Sets kthread_should_stop() for @k to return true, wakes it, and
 191  * waits for it to exit.  Your threadfn() must not call do_exit()
 192  * itself if you use this function!  This can also be called after
 193  * kthread_create() instead of calling wake_up_process(): the thread
 194  * will exit without calling threadfn().
 195  *
 196  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 197  * was never called.
 198  */
 199 int kthread_stop(struct task_struct *k)
 200 {
 201         int ret;
 202
 203         mutex_lock(&kthread_stop_lock);
 204
 205         /* It could exit after stop_info.k set, but before wake_up_process. */
 206         get_task_struct(k);
 207
 208         trace_sched_kthread_stop(k);
 209
 210         /* Must init completion *before* thread sees kthread_stop_info.k */
 211         init_completion(&kthread_stop_info.done);
 212         smp_wmb();
 213
 214         /* Now set kthread_should_stop() to true, and wake it up. */
 215         kthread_stop_info.k = k;
 216         wake_up_process(k);
 217         put_task_struct(k);
 218
 219         /* Once it dies, reset stop ptr, gather result and we're done. */
 220         wait_for_completion(&kthread_stop_info.done);
 221         kthread_stop_info.k = NULL;
 222         ret = kthread_stop_info.err;
 223         mutex_unlock(&kthread_stop_lock);
 224
 225         trace_sched_kthread_stop_ret(ret);
 226
 227         return ret;
 228 }
 229 EXPORT_SYMBOL(kthread_stop);
 230
 231 int kthreadd(void *unused)
 232 {
 233         struct task_struct *tsk = current;
 234
 235         /* Setup a clean context for our children to inherit. */
 236         set_task_comm(tsk, "kthreadd");
 237         ignore_signals(tsk);
 238         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 239         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 240         set_mems_allowed(node_possible_map);
 241
 242         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 243
 244         for (;;) {
 245                 set_current_state(TASK_INTERRUPTIBLE);
 246                 if (list_empty(&kthread_create_list))
 247                         schedule();
 248                 __set_current_state(TASK_RUNNING);
 249
 250                 spin_lock(&kthread_create_lock);
 251                 while (!list_empty(&kthread_create_list)) {
 252                         struct kthread_create_info *create;
 253
 254                         create = list_entry(kthread_create_list.next,
 255                                             struct kthread_create_info, list);
 256                         list_del_init(&create->list);
 257                         spin_unlock(&kthread_create_lock);
 258
 259                         create_kthread(create);
 260
 261                         spin_lock(&kthread_create_lock);
 262                 }
 263                 spin_unlock(&kthread_create_lock);
 264         }
 265
 266         return 0;
 267 }