lib/once.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/slab.h>
   3 #include <linux/spinlock.h>
   4 #include <linux/once.h>
   5 #include <linux/random.h>
   6 #include <linux/module.h>
   7
   8 struct once_work {
   9         struct work_struct work;
  10         struct static_key_true *key;
  11         struct module *module;
  12 };
  13
  14 static void once_deferred(struct work_struct *w)
  15 {
  16         struct once_work *work;
  17
  18         work = container_of(w, struct once_work, work);
  19         BUG_ON(!static_key_enabled(work->key));
  20         static_branch_disable(work->key);
  21         module_put(work->module);
  22         kfree(work);
  23 }
  24
  25 static void once_disable_jump(struct static_key_true *key, struct module *mod)
  26 {
  27         struct once_work *w;
  28
  29         w = kmalloc(sizeof(*w), GFP_ATOMIC);
  30         if (!w)
  31                 return;
  32
  33         INIT_WORK(&w->work, once_deferred);
  34         w->key = key;
  35         w->module = mod;
  36         __module_get(mod);
  37         schedule_work(&w->work);
  38 }
  39
  40 static DEFINE_SPINLOCK(once_lock);
  41
  42 bool __do_once_start(bool *done, unsigned long *flags)
  43         __acquires(once_lock)
  44 {
  45         spin_lock_irqsave(&once_lock, *flags);
  46         if (*done) {
  47                 spin_unlock_irqrestore(&once_lock, *flags);
  48                 /* Keep sparse happy by restoring an even lock count on
  49                  * this lock. In case we return here, we don't call into
  50                  * __do_once_done but return early in the DO_ONCE() macro.
  51                  */
  52                 __acquire(once_lock);
  53                 return false;
  54         }
  55
  56         return true;
  57 }
  58 EXPORT_SYMBOL(__do_once_start);
  59
  60 void __do_once_done(bool *done, struct static_key_true *once_key,
  61                     unsigned long *flags, struct module *mod)
  62         __releases(once_lock)
  63 {
  64         *done = true;
  65         spin_unlock_irqrestore(&once_lock, *flags);
  66         once_disable_jump(once_key, mod);
  67 }
  68 EXPORT_SYMBOL(__do_once_done);