LXR linux/kernel/task

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/spinlock.h>
   3#include <linux/task_work.h>
   4#include <linux/tracehook.h>
   5
   6static struct callback_head work_exited; /* all we need is ->next == NULL */
   7
   8/**
   9 * task_work_add - ask the @task to execute @work->func()
  10 * @task: the task which should run the callback
  11 * @work: the callback to run
  12 * @notify: send the notification if true
  13 *
  14 * Queue @work for task_work_run() below and notify the @task if @notify.
  15 * Fails if the @task is exiting/exited and thus it can't process this @work.
  16 * Otherwise @work->func() will be called when the @task returns from kernel
  17 * mode or exits.
  18 *
  19 * This is like the signal handler which runs in kernel mode, but it doesn't
  20 * try to wake up the @task.
  21 *
  22 * Note: there is no ordering guarantee on works queued here.
  23 *
  24 * RETURNS:
  25 * 0 if succeeds or -ESRCH.
  26 */
  27int
  28task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
  29{
  30        struct callback_head *head;
  31
  32        do {
  33                head = READ_ONCE(task->task_works);
  34                if (unlikely(head == &work_exited))
  35                        return -ESRCH;
  36                work->next = head;
  37        } while (cmpxchg(&task->task_works, head, work) != head);
  38
  39        if (notify)
  40                set_notify_resume(task);
  41        return 0;
  42}
  43
  44/**
  45 * task_work_cancel - cancel a pending work added by task_work_add()
  46 * @task: the task which should execute the work
  47 * @func: identifies the work to remove
  48 *
  49 * Find the last queued pending work with ->func == @func and remove
  50 * it from queue.
  51 *
  52 * RETURNS:
  53 * The found work or NULL if not found.
  54 */
  55struct callback_head *
  56task_work_cancel(struct task_struct *task, task_work_func_t func)
  57{
  58        struct callback_head **pprev = &task->task_works;
  59        struct callback_head *work;
  60        unsigned long flags;
  61
  62        if (likely(!task->task_works))
  63                return NULL;
  64        /*
  65         * If cmpxchg() fails we continue without updating pprev.
  66         * Either we raced with task_work_add() which added the
  67         * new entry before this work, we will find it again. Or
  68         * we raced with task_work_run(), *pprev == NULL/exited.
  69         */
  70        raw_spin_lock_irqsave(&task->pi_lock, flags);
  71        while ((work = READ_ONCE(*pprev))) {
  72                if (work->func != func)
  73                        pprev = &work->next;
  74                else if (cmpxchg(pprev, work, work->next) == work)
  75                        break;
  76        }
  77        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
  78
  79        return work;
  80}
  81
  82/**
  83 * task_work_run - execute the works added by task_work_add()
  84 *
  85 * Flush the pending works. Should be used by the core kernel code.
  86 * Called before the task returns to the user-mode or stops, or when
  87 * it exits. In the latter case task_work_add() can no longer add the
  88 * new work after task_work_run() returns.
  89 */
  90void task_work_run(void)
  91{
  92        struct task_struct *task = current;
  93        struct callback_head *work, *head, *next;
  94
  95        for (;;) {
  96                /*
  97                 * work->func() can do task_work_add(), do not set
  98                 * work_exited unless the list is empty.
  99                 */
 100                raw_spin_lock_irq(&task->pi_lock);
 101                do {
 102                        work = READ_ONCE(task->task_works);
 103                        head = !work && (task->flags & PF_EXITING) ?
 104                                &work_exited : NULL;
 105                } while (cmpxchg(&task->task_works, work, head) != work);
 106                raw_spin_unlock_irq(&task->pi_lock);
 107
 108                if (!work)
 109                        break;
 110
 111                do {
 112                        next = work->next;
 113                        work->func(work);
 114                        work = next;
 115                        cond_resched();
 116                } while (work);
 117        }
 118}
 119