projects/linux·blob cab9de71 · refs

182 lines · 5.0 KiB

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 do {
51 head = READ_ONCE(task->task_works);
52 if (unlikely(head == &work_exited))
53 return -ESRCH;
54 work->next = head;
55 } while (cmpxchg(&task->task_works, head, work) != head);
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 *
82 * RETURNS:
83 * The found work or NULL if not found.
84 */
85struct callback_head *
86task_work_cancel_match(struct task_struct *task,
87 bool (*match)(struct callback_head *, void *data),
88 void *data)
89{
90 struct callback_head **pprev = &task->task_works;
91 struct callback_head *work;
92 unsigned long flags;
93
94 if (likely(!task_work_pending(task)))
95 return NULL;
96 /*
97 * If cmpxchg() fails we continue without updating pprev.
98 * Either we raced with task_work_add() which added the
99 * new entry before this work, we will find it again. Or
100 * we raced with task_work_run(), *pprev == NULL/exited.
101 */
102 raw_spin_lock_irqsave(&task->pi_lock, flags);
103 while ((work = READ_ONCE(*pprev))) {
104 if (!match(work, data))
105 pprev = &work->next;
106 else if (cmpxchg(pprev, work, work->next) == work)
107 break;
108 }
109 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
110
111 return work;
112}
113
114static bool task_work_func_match(struct callback_head *cb, void *data)
115{
116 return cb->func == data;
117}
118
119/**
120 * task_work_cancel - cancel a pending work added by task_work_add()
121 * @task: the task which should execute the work
122 * @func: identifies the work to remove
123 *
124 * Find the last queued pending work with ->func == @func and remove
125 * it from queue.
126 *
127 * RETURNS:
128 * The found work or NULL if not found.
129 */
130struct callback_head *
131task_work_cancel(struct task_struct *task, task_work_func_t func)
132{
133 return task_work_cancel_match(task, task_work_func_match, func);
134}
135
136/**
137 * task_work_run - execute the works added by task_work_add()
138 *
139 * Flush the pending works. Should be used by the core kernel code.
140 * Called before the task returns to the user-mode or stops, or when
141 * it exits. In the latter case task_work_add() can no longer add the
142 * new work after task_work_run() returns.
143 */
144void task_work_run(void)
145{
146 struct task_struct *task = current;
147 struct callback_head *work, *head, *next;
148
149 for (;;) {
150 /*
151 * work->func() can do task_work_add(), do not set
152 * work_exited unless the list is empty.
153 */
154 do {
155 head = NULL;
156 work = READ_ONCE(task->task_works);
157 if (!work) {
158 if (task->flags & PF_EXITING)
159 head = &work_exited;
160 else
161 break;
162 }
163 } while (cmpxchg(&task->task_works, work, head) != work);
164
165 if (!work)
166 break;
167 /*
168 * Synchronize with task_work_cancel(). It can not remove
169 * the first entry == work, cmpxchg(task_works) must fail.
170 * But it can remove another entry from the ->next list.
171 */
172 raw_spin_lock_irq(&task->pi_lock);
173 raw_spin_unlock_irq(&task->pi_lock);
174
175 do {
176 next = work->next;
177 work->func(work);
178 work = next;
179 cond_resched();
180 } while (work);
181 }
182}