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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
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 * RETURNS:
22 * 0 if succeeds or -ESRCH.
23 */
24int
25task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
26{
27 struct callback_head *head;
28
29 do {
30 head = ACCESS_ONCE(task->task_works);
31 if (unlikely(head == &work_exited))
32 return -ESRCH;
33 work->next = head;
34 } while (cmpxchg(&task->task_works, head, work) != head);
35
36 if (notify)
37 set_notify_resume(task);
38 return 0;
39}
40
41/**
42 * task_work_cancel - cancel a pending work added by task_work_add()
43 * @task: the task which should execute the work
44 * @func: identifies the work to remove
45 *
46 * Find the last queued pending work with ->func == @func and remove
47 * it from queue.
48 *
49 * RETURNS:
50 * The found work or NULL if not found.
51 */
52struct callback_head *
53task_work_cancel(struct task_struct *task, task_work_func_t func)
54{
55 struct callback_head **pprev = &task->task_works;
56 struct callback_head *work;
57 unsigned long flags;
58 /*
59 * If cmpxchg() fails we continue without updating pprev.
60 * Either we raced with task_work_add() which added the
61 * new entry before this work, we will find it again. Or
62 * we raced with task_work_run(), *pprev == NULL/exited.
63 */
64 raw_spin_lock_irqsave(&task->pi_lock, flags);
65 while ((work = ACCESS_ONCE(*pprev))) {
66 smp_read_barrier_depends();
67 if (work->func != func)
68 pprev = &work->next;
69 else if (cmpxchg(pprev, work, work->next) == work)
70 break;
71 }
72 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
73
74 return work;
75}
76
77/**
78 * task_work_run - execute the works added by task_work_add()
79 *
80 * Flush the pending works. Should be used by the core kernel code.
81 * Called before the task returns to the user-mode or stops, or when
82 * it exits. In the latter case task_work_add() can no longer add the
83 * new work after task_work_run() returns.
84 */
85void task_work_run(void)
86{
87 struct task_struct *task = current;
88 struct callback_head *work, *head, *next;
89
90 for (;;) {
91 /*
92 * work->func() can do task_work_add(), do not set
93 * work_exited unless the list is empty.
94 */
95 do {
96 work = ACCESS_ONCE(task->task_works);
97 head = !work && (task->flags & PF_EXITING) ?
98 &work_exited : NULL;
99 } while (cmpxchg(&task->task_works, work, head) != work);
100
101 if (!work)
102 break;
103 /*
104 * Synchronize with task_work_cancel(). It can't remove
105 * the first entry == work, cmpxchg(task_works) should
106 * fail, but it can play with *work and other entries.
107 */
108 raw_spin_unlock_wait(&task->pi_lock);
109 smp_mb();
110
111 /* Reverse the list to run the works in fifo order */
112 head = NULL;
113 do {
114 next = work->next;
115 work->next = head;
116 head = work;
117 work = next;
118 } while (work);
119
120 work = head;
121 do {
122 next = work->next;
123 work->func(work);
124 work = next;
125 cond_resched();
126 } while (work);
127 }
128}