1// SPDX-License-Identifier: GPL-2.0
2#include <linux/spinlock.h>
3#include <linux/task_work.h>
4#include <linux/resume_user_mode.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: 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, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI.
16 *
17 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
18 * task and run the task_work, regardless of whether the task is currently
19 * running in the kernel or userspace.
20 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a
21 * reschedule IPI to force the targeted task to reschedule and run task_work.
22 * This can be advantageous if there's no strict requirement that the
23 * task_work be run as soon as possible, just whenever the task enters the
24 * kernel anyway.
25 * @TWA_RESUME work is run only when the task exits the kernel and returns to
26 * user mode, or before entering guest mode.
27 *
28 * Fails if the @task is exiting/exited and thus it can't process this @work.
29 * Otherwise @work->func() will be called when the @task goes through one of
30 * the aforementioned transitions, or exits.
31 *
32 * If the targeted task is exiting, then an error is returned and the work item
33 * is not queued. It's up to the caller to arrange for an alternative mechanism
34 * in that case.
35 *
36 * Note: there is no ordering guarantee on works queued here. The task_work
37 * list is LIFO.
38 *
39 * RETURNS:
40 * 0 if succeeds or -ESRCH.
41 */
42int task_work_add(struct task_struct *task, struct callback_head *work,
43		  enum task_work_notify_mode notify)
44{
45	struct callback_head *head;
46
47	/* record the work call stack in order to print it in KASAN reports */
48	kasan_record_aux_stack(work);
49
50	head = READ_ONCE(task->task_works);
51	do {
52		if (unlikely(head == &work_exited))
53			return -ESRCH;
54		work->next = head;
55	} while (!try_cmpxchg(&task->task_works, &head, work));
56
57	switch (notify) {
58	case TWA_NONE:
59		break;
60	case TWA_RESUME:
61		set_notify_resume(task);
62		break;
63	case TWA_SIGNAL:
64		set_notify_signal(task);
65		break;
66	case TWA_SIGNAL_NO_IPI:
67		__set_notify_signal(task);
68		break;
69	default:
70		WARN_ON_ONCE(1);
71		break;
72	}
73
74	return 0;
75}
76
77/**
78 * task_work_cancel_match - cancel a pending work added by task_work_add()
79 * @task: the task which should execute the work
80 * @match: match function to call
81 * @data: data to be passed in to match function
82 *
83 * RETURNS:
84 * The found work or NULL if not found.
85 */
86struct callback_head *
87task_work_cancel_match(struct task_struct *task,
88		       bool (*match)(struct callback_head *, void *data),
89		       void *data)
90{
91	struct callback_head **pprev = &task->task_works;
92	struct callback_head *work;
93	unsigned long flags;
94
95	if (likely(!task_work_pending(task)))
96		return NULL;
97	/*
98	 * If cmpxchg() fails we continue without updating pprev.
99	 * Either we raced with task_work_add() which added the
100	 * new entry before this work, we will find it again. Or
101	 * we raced with task_work_run(), *pprev == NULL/exited.
102	 */
103	raw_spin_lock_irqsave(&task->pi_lock, flags);
104	work = READ_ONCE(*pprev);
105	while (work) {
106		if (!match(work, data)) {
107			pprev = &work->next;
108			work = READ_ONCE(*pprev);
109		} else if (try_cmpxchg(pprev, &work, work->next))
110			break;
111	}
112	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
113
114	return work;
115}
116
117static bool task_work_func_match(struct callback_head *cb, void *data)
118{
119	return cb->func == data;
120}
121
122/**
123 * task_work_cancel - cancel a pending work added by task_work_add()
124 * @task: the task which should execute the work
125 * @func: identifies the work to remove
126 *
127 * Find the last queued pending work with ->func == @func and remove
128 * it from queue.
129 *
130 * RETURNS:
131 * The found work or NULL if not found.
132 */
133struct callback_head *
134task_work_cancel(struct task_struct *task, task_work_func_t func)
135{
136	return task_work_cancel_match(task, task_work_func_match, func);
137}
138
139/**
140 * task_work_run - execute the works added by task_work_add()
141 *
142 * Flush the pending works. Should be used by the core kernel code.
143 * Called before the task returns to the user-mode or stops, or when
144 * it exits. In the latter case task_work_add() can no longer add the
145 * new work after task_work_run() returns.
146 */
147void task_work_run(void)
148{
149	struct task_struct *task = current;
150	struct callback_head *work, *head, *next;
151
152	for (;;) {
153		/*
154		 * work->func() can do task_work_add(), do not set
155		 * work_exited unless the list is empty.
156		 */
157		work = READ_ONCE(task->task_works);
158		do {
159			head = NULL;
160			if (!work) {
161				if (task->flags & PF_EXITING)
162					head = &work_exited;
163				else
164					break;
165			}
166		} while (!try_cmpxchg(&task->task_works, &work, head));
167
168		if (!work)
169			break;
170		/*
171		 * Synchronize with task_work_cancel(). It can not remove
172		 * the first entry == work, cmpxchg(task_works) must fail.
173		 * But it can remove another entry from the ->next list.
174		 */
175		raw_spin_lock_irq(&task->pi_lock);
176		raw_spin_unlock_irq(&task->pi_lock);
177
178		do {
179			next = work->next;
180			work->func(work);
181			work = next;
182			cond_resched();
183		} while (work);
184	}
185}
186