1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/spinlock.h>
3 #include <linux/task_work.h>
4 #include <linux/tracehook.h>
5
6 static 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: how to notify the targeted task
13 *
14 * Queue @work for task_work_run() below and notify the @task if @notify
15 * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL works like signals, in that the
16 * it will interrupt the targeted task and run the task_work. @TWA_RESUME
17 * work is run only when the task exits the kernel and returns to user mode,
18 * or before entering guest mode. Fails if the @task is exiting/exited and thus
19 * it can't process this @work. Otherwise @work->func() will be called when the
20 * @task goes through one of the aforementioned transitions, or exits.
21 *
22 * If the targeted task is exiting, then an error is returned and the work item
23 * is not queued. It's up to the caller to arrange for an alternative mechanism
24 * in that case.
25 *
26 * Note: there is no ordering guarantee on works queued here. The task_work
27 * list is LIFO.
28 *
29 * RETURNS:
30 * 0 if succeeds or -ESRCH.
31 */
task_work_add(struct task_struct * task,struct callback_head * work,enum task_work_notify_mode notify)32 int task_work_add(struct task_struct *task, struct callback_head *work,
33 enum task_work_notify_mode notify)
34 {
35 struct callback_head *head;
36
37 do {
38 head = READ_ONCE(task->task_works);
39 if (unlikely(head == &work_exited))
40 return -ESRCH;
41 work->next = head;
42 } while (cmpxchg(&task->task_works, head, work) != head);
43
44 switch (notify) {
45 case TWA_NONE:
46 break;
47 case TWA_RESUME:
48 set_notify_resume(task);
49 break;
50 case TWA_SIGNAL:
51 set_notify_signal(task);
52 break;
53 default:
54 WARN_ON_ONCE(1);
55 break;
56 }
57
58 return 0;
59 }
60
61 /**
62 * task_work_cancel_match - cancel a pending work added by task_work_add()
63 * @task: the task which should execute the work
64 * @match: match function to call
65 *
66 * RETURNS:
67 * The found work or NULL if not found.
68 */
69 struct callback_head *
task_work_cancel_match(struct task_struct * task,bool (* match)(struct callback_head *,void * data),void * data)70 task_work_cancel_match(struct task_struct *task,
71 bool (*match)(struct callback_head *, void *data),
72 void *data)
73 {
74 struct callback_head **pprev = &task->task_works;
75 struct callback_head *work;
76 unsigned long flags;
77
78 if (likely(!task->task_works))
79 return NULL;
80 /*
81 * If cmpxchg() fails we continue without updating pprev.
82 * Either we raced with task_work_add() which added the
83 * new entry before this work, we will find it again. Or
84 * we raced with task_work_run(), *pprev == NULL/exited.
85 */
86 raw_spin_lock_irqsave(&task->pi_lock, flags);
87 while ((work = READ_ONCE(*pprev))) {
88 if (!match(work, data))
89 pprev = &work->next;
90 else if (cmpxchg(pprev, work, work->next) == work)
91 break;
92 }
93 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
94
95 return work;
96 }
97
task_work_func_match(struct callback_head * cb,void * data)98 static bool task_work_func_match(struct callback_head *cb, void *data)
99 {
100 return cb->func == data;
101 }
102
103 /**
104 * task_work_cancel - cancel a pending work added by task_work_add()
105 * @task: the task which should execute the work
106 * @func: identifies the work to remove
107 *
108 * Find the last queued pending work with ->func == @func and remove
109 * it from queue.
110 *
111 * RETURNS:
112 * The found work or NULL if not found.
113 */
114 struct callback_head *
task_work_cancel(struct task_struct * task,task_work_func_t func)115 task_work_cancel(struct task_struct *task, task_work_func_t func)
116 {
117 return task_work_cancel_match(task, task_work_func_match, func);
118 }
119
120 /**
121 * task_work_run - execute the works added by task_work_add()
122 *
123 * Flush the pending works. Should be used by the core kernel code.
124 * Called before the task returns to the user-mode or stops, or when
125 * it exits. In the latter case task_work_add() can no longer add the
126 * new work after task_work_run() returns.
127 */
task_work_run(void)128 void task_work_run(void)
129 {
130 struct task_struct *task = current;
131 struct callback_head *work, *head, *next;
132
133 for (;;) {
134 /*
135 * work->func() can do task_work_add(), do not set
136 * work_exited unless the list is empty.
137 */
138 do {
139 head = NULL;
140 work = READ_ONCE(task->task_works);
141 if (!work) {
142 if (task->flags & PF_EXITING)
143 head = &work_exited;
144 else
145 break;
146 }
147 } while (cmpxchg(&task->task_works, work, head) != work);
148
149 if (!work)
150 break;
151 /*
152 * Synchronize with task_work_cancel(). It can not remove
153 * the first entry == work, cmpxchg(task_works) must fail.
154 * But it can remove another entry from the ->next list.
155 */
156 raw_spin_lock_irq(&task->pi_lock);
157 raw_spin_unlock_irq(&task->pi_lock);
158
159 do {
160 next = work->next;
161 work->func(work);
162 work = next;
163 cond_resched();
164 } while (work);
165 }
166 }
167