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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 = READ_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 (likely(!task->task_works))
62 return NULL;
63 /*
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.
68 */
69 raw_spin_lock_irqsave(&task->pi_lock, flags);
70 while ((work = lockless_dereference(*pprev))) {
71 if (work->func != func)
72 pprev = &work->next;
73 else if (cmpxchg(pprev, work, work->next) == work)
74 break;
75 }
76 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
77
78 return work;
79}
80
81/**
82 * task_work_run - execute the works added by task_work_add()
83 *
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.
88 */
89void task_work_run(void)
90{
91 struct task_struct *task = current;
92 struct callback_head *work, *head, *next;
93
94 for (;;) {
95 /*
96 * work->func() can do task_work_add(), do not set
97 * work_exited unless the list is empty.
98 */
99 do {
100 work = READ_ONCE(task->task_works);
101 head = !work && (task->flags & PF_EXITING) ?
102 &work_exited : NULL;
103 } while (cmpxchg(&task->task_works, work, head) != work);
104
105 if (!work)
106 break;
107 /*
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.
111 */
112 raw_spin_unlock_wait(&task->pi_lock);
113
114 do {
115 next = work->next;
116 work->func(work);
117 work = next;
118 cond_resched();
119 } while (work);
120 }
121}
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}