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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 *
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 work = READ_ONCE(*pprev);
104 while (work) {
105 if (!match(work, data)) {
106 pprev = &work->next;
107 work = READ_ONCE(*pprev);
108 } else if (try_cmpxchg(pprev, &work, work->next))
109 break;
110 }
111 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
112
113 return work;
114}
115
116static bool task_work_func_match(struct callback_head *cb, void *data)
117{
118 return cb->func == data;
119}
120
121/**
122 * task_work_cancel - cancel a pending work added by task_work_add()
123 * @task: the task which should execute the work
124 * @func: identifies the work to remove
125 *
126 * Find the last queued pending work with ->func == @func and remove
127 * it from queue.
128 *
129 * RETURNS:
130 * The found work or NULL if not found.
131 */
132struct callback_head *
133task_work_cancel(struct task_struct *task, task_work_func_t func)
134{
135 return task_work_cancel_match(task, task_work_func_match, func);
136}
137
138/**
139 * task_work_run - execute the works added by task_work_add()
140 *
141 * Flush the pending works. Should be used by the core kernel code.
142 * Called before the task returns to the user-mode or stops, or when
143 * it exits. In the latter case task_work_add() can no longer add the
144 * new work after task_work_run() returns.
145 */
146void task_work_run(void)
147{
148 struct task_struct *task = current;
149 struct callback_head *work, *head, *next;
150
151 for (;;) {
152 /*
153 * work->func() can do task_work_add(), do not set
154 * work_exited unless the list is empty.
155 */
156 work = READ_ONCE(task->task_works);
157 do {
158 head = NULL;
159 if (!work) {
160 if (task->flags & PF_EXITING)
161 head = &work_exited;
162 else
163 break;
164 }
165 } while (!try_cmpxchg(&task->task_works, &work, head));
166
167 if (!work)
168 break;
169 /*
170 * Synchronize with task_work_cancel(). It can not remove
171 * the first entry == work, cmpxchg(task_works) must fail.
172 * But it can remove another entry from the ->next list.
173 */
174 raw_spin_lock_irq(&task->pi_lock);
175 raw_spin_unlock_irq(&task->pi_lock);
176
177 do {
178 next = work->next;
179 work->func(work);
180 work = next;
181 cond_resched();
182 } while (work);
183 }
184}
1#include <linux/spinlock.h>
2#include <linux/task_work.h>
3#include <linux/tracehook.h>
4
5int
6task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
7{
8 unsigned long flags;
9 int err = -ESRCH;
10
11#ifndef TIF_NOTIFY_RESUME
12 if (notify)
13 return -ENOTSUPP;
14#endif
15 /*
16 * We must not insert the new work if the task has already passed
17 * exit_task_work(). We rely on do_exit()->raw_spin_unlock_wait()
18 * and check PF_EXITING under pi_lock.
19 */
20 raw_spin_lock_irqsave(&task->pi_lock, flags);
21 if (likely(!(task->flags & PF_EXITING))) {
22 hlist_add_head(&twork->hlist, &task->task_works);
23 err = 0;
24 }
25 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
26
27 /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
28 if (likely(!err) && notify)
29 set_notify_resume(task);
30 return err;
31}
32
33struct task_work *
34task_work_cancel(struct task_struct *task, task_work_func_t func)
35{
36 unsigned long flags;
37 struct task_work *twork;
38 struct hlist_node *pos;
39
40 raw_spin_lock_irqsave(&task->pi_lock, flags);
41 hlist_for_each_entry(twork, pos, &task->task_works, hlist) {
42 if (twork->func == func) {
43 hlist_del(&twork->hlist);
44 goto found;
45 }
46 }
47 twork = NULL;
48 found:
49 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
50
51 return twork;
52}
53
54void task_work_run(void)
55{
56 struct task_struct *task = current;
57 struct hlist_head task_works;
58 struct hlist_node *pos;
59
60 raw_spin_lock_irq(&task->pi_lock);
61 hlist_move_list(&task->task_works, &task_works);
62 raw_spin_unlock_irq(&task->pi_lock);
63
64 if (unlikely(hlist_empty(&task_works)))
65 return;
66 /*
67 * We use hlist to save the space in task_struct, but we want fifo.
68 * Find the last entry, the list should be short, then process them
69 * in reverse order.
70 */
71 for (pos = task_works.first; pos->next; pos = pos->next)
72 ;
73
74 for (;;) {
75 struct hlist_node **pprev = pos->pprev;
76 struct task_work *twork = container_of(pos, struct task_work,
77 hlist);
78 twork->func(twork);
79
80 if (pprev == &task_works.first)
81 break;
82 pos = container_of(pprev, struct hlist_node, next);
83 }
84}