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/unistd.h>
  13 #include <linux/file.h>
  14 #include <linux/module.h>
  15 #include <linux/mutex.h>
  16 #include <trace/events/sched.h>
  17
  18 #define KTHREAD_NICE_LEVEL (-5)
  19
  20 static DEFINE_SPINLOCK(kthread_create_lock);
  21 static LIST_HEAD(kthread_create_list);
  22 struct task_struct *kthreadd_task;
  23
  24 struct kthread_create_info
  25 {
  26         /* Information passed to kthread() from kthreadd. */
  27         int (*threadfn)(void *data);
  28         void *data;
  29         struct completion started;
  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_stop_info
  39 {
  40         struct task_struct *k;
  41         int err;
  42         struct completion done;
  43 };
  44
  45 /* Thread stopping is done by setthing this var: lock serializes
  46  * multiple kthread_stop calls. */
  47 static DEFINE_MUTEX(kthread_stop_lock);
  48 static struct kthread_stop_info kthread_stop_info;
  49
  50 /**
  51  * kthread_should_stop - should this kthread return now?
  52  *
  53  * When someone calls kthread_stop() on your kthread, it will be woken
  54  * and this will return true.  You should then return, and your return
  55  * value will be passed through to kthread_stop().
  56  */
  57 int kthread_should_stop(void)
  58 {
  59         return (kthread_stop_info.k == current);
  60 }
  61 EXPORT_SYMBOL(kthread_should_stop);
  62
  63 static int kthread(void *_create)
  64 {
  65         struct kthread_create_info *create = _create;
  66         int (*threadfn)(void *data);
  67         void *data;
  68         int ret = -EINTR;
  69
  70         /* Copy data: it's on kthread's stack */
  71         threadfn = create->threadfn;
  72         data = create->data;
  73
  74         /* OK, tell user we're spawned, wait for stop or wakeup */
  75         __set_current_state(TASK_UNINTERRUPTIBLE);
  76         create->result = current;
  77         complete(&create->started);
  78         schedule();
  79
  80         if (!kthread_should_stop())
  81                 ret = threadfn(data);
  82
  83         /* It might have exited on its own, w/o kthread_stop.  Check. */
  84         if (kthread_should_stop()) {
  85                 kthread_stop_info.err = ret;
  86                 complete(&kthread_stop_info.done);
  87         }
  88         return 0;
  89 }
  90
  91 static void create_kthread(struct kthread_create_info *create)
  92 {
  93         int pid;
  94
  95         /* We want our own signal handler (we take no signals by default). */
  96         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  97         if (pid < 0)
  98                 create->result = ERR_PTR(pid);
  99         else
 100                 wait_for_completion(&create->started);
 101         complete(&create->done);
 102 }
 103
 104 /**
 105  * kthread_create - create a kthread.
 106  * @threadfn: the function to run until signal_pending(current).
 107  * @data: data ptr for @threadfn.
 108  * @namefmt: printf-style name for the thread.
 109  *
 110  * Description: This helper function creates and names a kernel
 111  * thread.  The thread will be stopped: use wake_up_process() to start
 112  * it.  See also kthread_run(), kthread_create_on_cpu().
 113  *
 114  * When woken, the thread will run @threadfn() with @data as its
 115  * argument. @threadfn() can either call do_exit() directly if it is a
 116  * standalone thread for which noone will call kthread_stop(), or
 117  * return when 'kthread_should_stop()' is true (which means
 118  * kthread_stop() has been called).  The return value should be zero
 119  * or a negative error number; it will be passed to kthread_stop().
 120  *
 121  * Returns a task_struct or ERR_PTR(-ENOMEM).
 122  */
 123 struct task_struct *kthread_create(int (*threadfn)(void *data),
 124                                    void *data,
 125                                    const char namefmt[],
 126                                    ...)
 127 {
 128         struct kthread_create_info create;
 129
 130         create.threadfn = threadfn;
 131         create.data = data;
 132         init_completion(&create.started);
 133         init_completion(&create.done);
 134
 135         spin_lock(&kthread_create_lock);
 136         list_add_tail(&create.list, &kthread_create_list);
 137         spin_unlock(&kthread_create_lock);
 138
 139         wake_up_process(kthreadd_task);
 140         wait_for_completion(&create.done);
 141
 142         if (!IS_ERR(create.result)) {
 143                 struct sched_param param = { .sched_priority = 0 };
 144                 va_list args;
 145
 146                 va_start(args, namefmt);
 147                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 148                           namefmt, args);
 149                 va_end(args);
 150                 /*
 151                  * root may have changed our (kthreadd's) priority or CPU mask.
 152                  * The kernel thread should not inherit these properties.
 153                  */
 154                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 155                 set_user_nice(create.result, KTHREAD_NICE_LEVEL);
 156                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 157         }
 158         return create.result;
 159 }
 160 EXPORT_SYMBOL(kthread_create);
 161
 162 /**
 163  * kthread_bind - bind a just-created kthread to a cpu.
 164  * @k: thread created by kthread_create().
 165  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 166  *
 167  * Description: This function is equivalent to set_cpus_allowed(),
 168  * except that @cpu doesn't need to be online, and the thread must be
 169  * stopped (i.e., just returned from kthread_create()).
 170  */
 171 void kthread_bind(struct task_struct *k, unsigned int cpu)
 172 {
 173         /* Must have done schedule() in kthread() before we set_task_cpu */
 174         if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
 175                 WARN_ON(1);
 176                 return;
 177         }
 178         set_task_cpu(k, cpu);
 179         k->cpus_allowed = cpumask_of_cpu(cpu);
 180         k->rt.nr_cpus_allowed = 1;
 181         k->flags |= PF_THREAD_BOUND;
 182 }
 183 EXPORT_SYMBOL(kthread_bind);
 184
 185 /**
 186  * kthread_stop - stop a thread created by kthread_create().
 187  * @k: thread created by kthread_create().
 188  *
 189  * Sets kthread_should_stop() for @k to return true, wakes it, and
 190  * waits for it to exit.  Your threadfn() must not call do_exit()
 191  * itself if you use this function!  This can also be called after
 192  * kthread_create() instead of calling wake_up_process(): the thread
 193  * will exit without calling threadfn().
 194  *
 195  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 196  * was never called.
 197  */
 198 int kthread_stop(struct task_struct *k)
 199 {
 200         int ret;
 201
 202         mutex_lock(&kthread_stop_lock);
 203
 204         /* It could exit after stop_info.k set, but before wake_up_process. */
 205         get_task_struct(k);
 206
 207         trace_sched_kthread_stop(k);
 208
 209         /* Must init completion *before* thread sees kthread_stop_info.k */
 210         init_completion(&kthread_stop_info.done);
 211         smp_wmb();
 212
 213         /* Now set kthread_should_stop() to true, and wake it up. */
 214         kthread_stop_info.k = k;
 215         wake_up_process(k);
 216         put_task_struct(k);
 217
 218         /* Once it dies, reset stop ptr, gather result and we're done. */
 219         wait_for_completion(&kthread_stop_info.done);
 220         kthread_stop_info.k = NULL;
 221         ret = kthread_stop_info.err;
 222         mutex_unlock(&kthread_stop_lock);
 223
 224         trace_sched_kthread_stop_ret(ret);
 225
 226         return ret;
 227 }
 228 EXPORT_SYMBOL(kthread_stop);
 229
 230 int kthreadd(void *unused)
 231 {
 232         struct task_struct *tsk = current;
 233
 234         /* Setup a clean context for our children to inherit. */
 235         set_task_comm(tsk, "kthreadd");
 236         ignore_signals(tsk);
 237         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 238         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 239
 240         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 241
 242         for (;;) {
 243                 set_current_state(TASK_INTERRUPTIBLE);
 244                 if (list_empty(&kthread_create_list))
 245                         schedule();
 246                 __set_current_state(TASK_RUNNING);
 247
 248                 spin_lock(&kthread_create_lock);
 249                 while (!list_empty(&kthread_create_list)) {
 250                         struct kthread_create_info *create;
 251
 252                         create = list_entry(kthread_create_list.next,
 253                                             struct kthread_create_info, list);
 254                         list_del_init(&create->list);
 255                         spin_unlock(&kthread_create_lock);
 256
 257                         create_kthread(create);
 258
 259                         spin_lock(&kthread_create_lock);
 260                 }
 261                 spin_unlock(&kthread_create_lock);
 262         }
 263
 264         return 0;
 265 }