LXR linux/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
   8struct once_work {
   9        struct work_struct work;
  10        struct static_key_true *key;
  11        struct module *module;
  12};
  13
  14static 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
  25static 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
  40static DEFINE_SPINLOCK(once_lock);
  41
  42bool __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}
  58EXPORT_SYMBOL(__do_once_start);
  59
  60void __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}
  68EXPORT_SYMBOL(__do_once_done);
  69