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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// 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, int notify)
29{
30 struct callback_head *head;
31 unsigned long flags;
32
33 do {
34 head = READ_ONCE(task->task_works);
35 if (unlikely(head == &work_exited))
36 return -ESRCH;
37 work->next = head;
38 } while (cmpxchg(&task->task_works, head, work) != head);
39
40 switch (notify) {
41 case TWA_RESUME:
42 set_notify_resume(task);
43 break;
44 case TWA_SIGNAL:
45 /*
46 * Only grab the sighand lock if we don't already have some
47 * task_work pending. This pairs with the smp_store_mb()
48 * in get_signal(), see comment there.
49 */
50 if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
51 lock_task_sighand(task, &flags)) {
52 task->jobctl |= JOBCTL_TASK_WORK;
53 signal_wake_up(task, 0);
54 unlock_task_sighand(task, &flags);
55 }
56 break;
57 }
58
59 return 0;
60}
61
62/**
63 * task_work_cancel - cancel a pending work added by task_work_add()
64 * @task: the task which should execute the work
65 * @func: identifies the work to remove
66 *
67 * Find the last queued pending work with ->func == @func and remove
68 * it from queue.
69 *
70 * RETURNS:
71 * The found work or NULL if not found.
72 */
73struct callback_head *
74task_work_cancel(struct task_struct *task, task_work_func_t func)
75{
76 struct callback_head **pprev = &task->task_works;
77 struct callback_head *work;
78 unsigned long flags;
79
80 if (likely(!task->task_works))
81 return NULL;
82 /*
83 * If cmpxchg() fails we continue without updating pprev.
84 * Either we raced with task_work_add() which added the
85 * new entry before this work, we will find it again. Or
86 * we raced with task_work_run(), *pprev == NULL/exited.
87 */
88 raw_spin_lock_irqsave(&task->pi_lock, flags);
89 while ((work = READ_ONCE(*pprev))) {
90 if (work->func != func)
91 pprev = &work->next;
92 else if (cmpxchg(pprev, work, work->next) == work)
93 break;
94 }
95 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
96
97 return work;
98}
99
100/**
101 * task_work_run - execute the works added by task_work_add()
102 *
103 * Flush the pending works. Should be used by the core kernel code.
104 * Called before the task returns to the user-mode or stops, or when
105 * it exits. In the latter case task_work_add() can no longer add the
106 * new work after task_work_run() returns.
107 */
108void task_work_run(void)
109{
110 struct task_struct *task = current;
111 struct callback_head *work, *head, *next;
112
113 for (;;) {
114 /*
115 * work->func() can do task_work_add(), do not set
116 * work_exited unless the list is empty.
117 */
118 do {
119 head = NULL;
120 work = READ_ONCE(task->task_works);
121 if (!work) {
122 if (task->flags & PF_EXITING)
123 head = &work_exited;
124 else
125 break;
126 }
127 } while (cmpxchg(&task->task_works, work, head) != work);
128
129 if (!work)
130 break;
131 /*
132 * Synchronize with task_work_cancel(). It can not remove
133 * the first entry == work, cmpxchg(task_works) must fail.
134 * But it can remove another entry from the ->next list.
135 */
136 raw_spin_lock_irq(&task->pi_lock);
137 raw_spin_unlock_irq(&task->pi_lock);
138
139 do {
140 next = work->next;
141 work->func(work);
142 work = next;
143 cond_resched();
144 } while (work);
145 }
146}