projects/linux·blob d37a14bb · refs

120 lines · 3.2 KiB

1#include <linux/spinlock.h>
2#include <linux/task_work.h>
3#include <linux/tracehook.h>
4
5static struct callback_head work_exited; /* all we need is ->next == NULL */
6
7/**
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
12 *
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
16 * mode or exits.
17 *
18 * This is like the signal handler which runs in kernel mode, but it doesn't
19 * try to wake up the @task.
20 *
21 * Note: there is no ordering guarantee on works queued here.
22 *
23 * RETURNS:
24 * 0 if succeeds or -ESRCH.
25 */
26int
27task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
28{
29 struct callback_head *head;
30
31 do {
32 head = ACCESS_ONCE(task->task_works);
33 if (unlikely(head == &work_exited))
34 return -ESRCH;
35 work->next = head;
36 } while (cmpxchg(&task->task_works, head, work) != head);
37
38 if (notify)
39 set_notify_resume(task);
40 return 0;
41}
42
43/**
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
47 *
48 * Find the last queued pending work with ->func == @func and remove
49 * it from queue.
50 *
51 * RETURNS:
52 * The found work or NULL if not found.
53 */
54struct callback_head *
55task_work_cancel(struct task_struct *task, task_work_func_t func)
56{
57 struct callback_head **pprev = &task->task_works;
58 struct callback_head *work;
59 unsigned long flags;
60 /*
61 * If cmpxchg() fails we continue without updating pprev.
62 * Either we raced with task_work_add() which added the
63 * new entry before this work, we will find it again. Or
64 * we raced with task_work_run(), *pprev == NULL/exited.
65 */
66 raw_spin_lock_irqsave(&task->pi_lock, flags);
67 while ((work = ACCESS_ONCE(*pprev))) {
68 smp_read_barrier_depends();
69 if (work->func != func)
70 pprev = &work->next;
71 else if (cmpxchg(pprev, work, work->next) == work)
72 break;
73 }
74 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
75
76 return work;
77}
78
79/**
80 * task_work_run - execute the works added by task_work_add()
81 *
82 * Flush the pending works. Should be used by the core kernel code.
83 * Called before the task returns to the user-mode or stops, or when
84 * it exits. In the latter case task_work_add() can no longer add the
85 * new work after task_work_run() returns.
86 */
87void task_work_run(void)
88{
89 struct task_struct *task = current;
90 struct callback_head *work, *head, *next;
91
92 for (;;) {
93 /*
94 * work->func() can do task_work_add(), do not set
95 * work_exited unless the list is empty.
96 */
97 do {
98 work = ACCESS_ONCE(task->task_works);
99 head = !work && (task->flags & PF_EXITING) ?
100 &work_exited : NULL;
101 } while (cmpxchg(&task->task_works, work, head) != work);
102
103 if (!work)
104 break;
105 /*
106 * Synchronize with task_work_cancel(). It can't remove
107 * the first entry == work, cmpxchg(task_works) should
108 * fail, but it can play with *work and other entries.
109 */
110 raw_spin_unlock_wait(&task->pi_lock);
111 smp_mb();
112
113 do {
114 next = work->next;
115 work->func(work);
116 work = next;
117 cond_resched();
118 } while (work);
119 }
120}