1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/spinlock.h>
3 #include <linux/task_work.h>
4 #include <linux/tracehook.h>
6 static struct callback_head work_exited; /* all we need is ->next == NULL */
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
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
19 * This is like the signal handler which runs in kernel mode, but it doesn't
20 * try to wake up the @task.
22 * Note: there is no ordering guarantee on works queued here.
25 * 0 if succeeds or -ESRCH.
28 task_work_add(struct task_struct *task, struct callback_head *work, int notify)
30 struct callback_head *head;
34 head = READ_ONCE(task->task_works);
35 if (unlikely(head == &work_exited))
38 } while (cmpxchg(&task->task_works, head, work) != head);
42 set_notify_resume(task);
46 * Only grab the sighand lock if we don't already have some
47 * task_work pending. This pairs with the smp_store_mb()
48 * in get_signal(), see comment there.
50 if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
51 lock_task_sighand(task, &flags)) {
52 task->jobctl |= JOBCTL_TASK_WORK;
53 signal_wake_up(task, 0);
54 unlock_task_sighand(task, &flags);
63 * task_work_cancel - cancel a pending work added by task_work_add()
64 * @task: the task which should execute the work
65 * @func: identifies the work to remove
67 * Find the last queued pending work with ->func == @func and remove
71 * The found work or NULL if not found.
73 struct callback_head *
74 task_work_cancel(struct task_struct *task, task_work_func_t func)
76 struct callback_head **pprev = &task->task_works;
77 struct callback_head *work;
80 if (likely(!task->task_works))
83 * If cmpxchg() fails we continue without updating pprev.
84 * Either we raced with task_work_add() which added the
85 * new entry before this work, we will find it again. Or
86 * we raced with task_work_run(), *pprev == NULL/exited.
88 raw_spin_lock_irqsave(&task->pi_lock, flags);
89 while ((work = READ_ONCE(*pprev))) {
90 if (work->func != func)
92 else if (cmpxchg(pprev, work, work->next) == work)
95 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
101 * task_work_run - execute the works added by task_work_add()
103 * Flush the pending works. Should be used by the core kernel code.
104 * Called before the task returns to the user-mode or stops, or when
105 * it exits. In the latter case task_work_add() can no longer add the
106 * new work after task_work_run() returns.
108 void task_work_run(void)
110 struct task_struct *task = current;
111 struct callback_head *work, *head, *next;
115 * work->func() can do task_work_add(), do not set
116 * work_exited unless the list is empty.
120 work = READ_ONCE(task->task_works);
122 if (task->flags & PF_EXITING)
127 } while (cmpxchg(&task->task_works, work, head) != work);
132 * Synchronize with task_work_cancel(). It can not remove
133 * the first entry == work, cmpxchg(task_works) must fail.
134 * But it can remove another entry from the ->next list.
136 raw_spin_lock_irq(&task->pi_lock);
137 raw_spin_unlock_irq(&task->pi_lock);