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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}
1#include <linux/spinlock.h>
2#include <linux/task_work.h>
3#include <linux/tracehook.h>
4
5int
6task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
7{
8 unsigned long flags;
9 int err = -ESRCH;
10
11#ifndef TIF_NOTIFY_RESUME
12 if (notify)
13 return -ENOTSUPP;
14#endif
15 /*
16 * We must not insert the new work if the task has already passed
17 * exit_task_work(). We rely on do_exit()->raw_spin_unlock_wait()
18 * and check PF_EXITING under pi_lock.
19 */
20 raw_spin_lock_irqsave(&task->pi_lock, flags);
21 if (likely(!(task->flags & PF_EXITING))) {
22 hlist_add_head(&twork->hlist, &task->task_works);
23 err = 0;
24 }
25 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
26
27 /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
28 if (likely(!err) && notify)
29 set_notify_resume(task);
30 return err;
31}
32
33struct task_work *
34task_work_cancel(struct task_struct *task, task_work_func_t func)
35{
36 unsigned long flags;
37 struct task_work *twork;
38 struct hlist_node *pos;
39
40 raw_spin_lock_irqsave(&task->pi_lock, flags);
41 hlist_for_each_entry(twork, pos, &task->task_works, hlist) {
42 if (twork->func == func) {
43 hlist_del(&twork->hlist);
44 goto found;
45 }
46 }
47 twork = NULL;
48 found:
49 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
50
51 return twork;
52}
53
54void task_work_run(void)
55{
56 struct task_struct *task = current;
57 struct hlist_head task_works;
58 struct hlist_node *pos;
59
60 raw_spin_lock_irq(&task->pi_lock);
61 hlist_move_list(&task->task_works, &task_works);
62 raw_spin_unlock_irq(&task->pi_lock);
63
64 if (unlikely(hlist_empty(&task_works)))
65 return;
66 /*
67 * We use hlist to save the space in task_struct, but we want fifo.
68 * Find the last entry, the list should be short, then process them
69 * in reverse order.
70 */
71 for (pos = task_works.first; pos->next; pos = pos->next)
72 ;
73
74 for (;;) {
75 struct hlist_node **pprev = pos->pprev;
76 struct task_work *twork = container_of(pos, struct task_work,
77 hlist);
78 twork->func(twork);
79
80 if (pprev == &task_works.first)
81 break;
82 pos = container_of(pprev, struct hlist_node, next);
83 }
84}