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: how to notify the targeted task
14 * Queue @work for task_work_run() below and notify the @task if @notify
15 * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL works like signals, in that the
16 * it will interrupt the targeted task and run the task_work. @TWA_RESUME
17 * work is run only when the task exits the kernel and returns to user mode,
18 * or before entering guest mode. Fails if the @task is exiting/exited and thus
19 * it can't process this @work. Otherwise @work->func() will be called when the
20 * @task goes through one of the aforementioned transitions, or exits.
22 * If the targeted task is exiting, then an error is returned and the work item
23 * is not queued. It's up to the caller to arrange for an alternative mechanism
26 * Note: there is no ordering guarantee on works queued here. The task_work
30 * 0 if succeeds or -ESRCH.
32 int task_work_add(struct task_struct *task, struct callback_head *work,
33 enum task_work_notify_mode notify)
35 struct callback_head *head;
38 head = READ_ONCE(task->task_works);
39 if (unlikely(head == &work_exited))
42 } while (cmpxchg(&task->task_works, head, work) != head);
48 set_notify_resume(task);
51 set_notify_signal(task);
62 * task_work_cancel - cancel a pending work added by task_work_add()
63 * @task: the task which should execute the work
64 * @func: identifies the work to remove
66 * Find the last queued pending work with ->func == @func and remove
70 * The found work or NULL if not found.
72 struct callback_head *
73 task_work_cancel(struct task_struct *task, task_work_func_t func)
75 struct callback_head **pprev = &task->task_works;
76 struct callback_head *work;
79 if (likely(!task->task_works))
82 * If cmpxchg() fails we continue without updating pprev.
83 * Either we raced with task_work_add() which added the
84 * new entry before this work, we will find it again. Or
85 * we raced with task_work_run(), *pprev == NULL/exited.
87 raw_spin_lock_irqsave(&task->pi_lock, flags);
88 while ((work = READ_ONCE(*pprev))) {
89 if (work->func != func)
91 else if (cmpxchg(pprev, work, work->next) == work)
94 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
100 * task_work_run - execute the works added by task_work_add()
102 * Flush the pending works. Should be used by the core kernel code.
103 * Called before the task returns to the user-mode or stops, or when
104 * it exits. In the latter case task_work_add() can no longer add the
105 * new work after task_work_run() returns.
107 void task_work_run(void)
109 struct task_struct *task = current;
110 struct callback_head *work, *head, *next;
114 * work->func() can do task_work_add(), do not set
115 * work_exited unless the list is empty.
119 work = READ_ONCE(task->task_works);
121 if (task->flags & PF_EXITING)
126 } while (cmpxchg(&task->task_works, work, head) != work);
131 * Synchronize with task_work_cancel(). It can not remove
132 * the first entry == work, cmpxchg(task_works) must fail.
133 * But it can remove another entry from the ->next list.
135 raw_spin_lock_irq(&task->pi_lock);
136 raw_spin_unlock_irq(&task->pi_lock);