1 #include <linux/spinlock.h>
2 #include <linux/task_work.h>
3 #include <linux/tracehook.h>
5 static struct callback_head work_exited; /* all we need is ->next == NULL */
8 * task_work_add - ask the @task to execute @work->func()
9 * @task: the task which should run the callback
10 * @work: the callback to run
11 * @notify: send the notification if true
13 * Queue @work for task_work_run() below and notify the @task if @notify.
14 * Fails if the @task is exiting/exited and thus it can't process this @work.
15 * Otherwise @work->func() will be called when the @task returns from kernel
18 * This is like the signal handler which runs in kernel mode, but it doesn't
19 * try to wake up the @task.
21 * Note: there is no ordering guarantee on works queued here.
24 * 0 if succeeds or -ESRCH.
27 task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
29 struct callback_head *head;
32 head = READ_ONCE(task->task_works);
33 if (unlikely(head == &work_exited))
36 } while (cmpxchg(&task->task_works, head, work) != head);
39 set_notify_resume(task);
44 * task_work_cancel - cancel a pending work added by task_work_add()
45 * @task: the task which should execute the work
46 * @func: identifies the work to remove
48 * Find the last queued pending work with ->func == @func and remove
52 * The found work or NULL if not found.
54 struct callback_head *
55 task_work_cancel(struct task_struct *task, task_work_func_t func)
57 struct callback_head **pprev = &task->task_works;
58 struct callback_head *work;
61 if (likely(!task->task_works))
64 * If cmpxchg() fails we continue without updating pprev.
65 * Either we raced with task_work_add() which added the
66 * new entry before this work, we will find it again. Or
67 * we raced with task_work_run(), *pprev == NULL/exited.
69 raw_spin_lock_irqsave(&task->pi_lock, flags);
70 while ((work = lockless_dereference(*pprev))) {
71 if (work->func != func)
73 else if (cmpxchg(pprev, work, work->next) == work)
76 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
82 * task_work_run - execute the works added by task_work_add()
84 * Flush the pending works. Should be used by the core kernel code.
85 * Called before the task returns to the user-mode or stops, or when
86 * it exits. In the latter case task_work_add() can no longer add the
87 * new work after task_work_run() returns.
89 void task_work_run(void)
91 struct task_struct *task = current;
92 struct callback_head *work, *head, *next;
96 * work->func() can do task_work_add(), do not set
97 * work_exited unless the list is empty.
100 work = READ_ONCE(task->task_works);
101 head = !work && (task->flags & PF_EXITING) ?
103 } while (cmpxchg(&task->task_works, work, head) != work);
108 * Synchronize with task_work_cancel(). It can't remove
109 * the first entry == work, cmpxchg(task_works) should
110 * fail, but it can play with *work and other entries.
112 raw_spin_unlock_wait(&task->pi_lock);