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 /* record the work call stack in order to print it in KASAN reports */
38 kasan_record_aux_stack(work);
39
40 do {
41 head = READ_ONCE(task->task_works);
42 if (unlikely(head == &work_exited))
43 return -ESRCH;
44 work->next = head;
45 } while (cmpxchg(&task->task_works, head, work) != head);
46
47 switch (notify) {
48 case TWA_NONE:
49 break;
50 case TWA_RESUME:
51 set_notify_resume(task);
52 break;
53 case TWA_SIGNAL:
54 set_notify_signal(task);
55 break;
56 default:
57 WARN_ON_ONCE(1);
58 break;
59 }
60
61 return 0;
62 }
63
64 /**
65 * task_work_cancel_match - cancel a pending work added by task_work_add()
66 * @task: the task which should execute the work
67 * @match: match function to call
68 *
69 * RETURNS:
70 * The found work or NULL if not found.
71 */
72 struct callback_head *
task_work_cancel_match(struct task_struct * task,bool (* match)(struct callback_head *,void * data),void * data)73 task_work_cancel_match(struct task_struct *task,
74 bool (*match)(struct callback_head *, void *data),
75 void *data)
76 {
77 struct callback_head **pprev = &task->task_works;
78 struct callback_head *work;
79 unsigned long flags;
80
81 if (likely(!task->task_works))
82 return NULL;
83 /*
84 * If cmpxchg() fails we continue without updating pprev.
85 * Either we raced with task_work_add() which added the
86 * new entry before this work, we will find it again. Or
87 * we raced with task_work_run(), *pprev == NULL/exited.
88 */
89 raw_spin_lock_irqsave(&task->pi_lock, flags);
90 while ((work = READ_ONCE(*pprev))) {
91 if (!match(work, data))
92 pprev = &work->next;
93 else if (cmpxchg(pprev, work, work->next) == work)
94 break;
95 }
96 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
97
98 return work;
99 }
100
task_work_func_match(struct callback_head * cb,void * data)101 static bool task_work_func_match(struct callback_head *cb, void *data)
102 {
103 return cb->func == data;
104 }
105
106 /**
107 * task_work_cancel - cancel a pending work added by task_work_add()
108 * @task: the task which should execute the work
109 * @func: identifies the work to remove
110 *
111 * Find the last queued pending work with ->func == @func and remove
112 * it from queue.
113 *
114 * RETURNS:
115 * The found work or NULL if not found.
116 */
117 struct callback_head *
task_work_cancel(struct task_struct * task,task_work_func_t func)118 task_work_cancel(struct task_struct *task, task_work_func_t func)
119 {
120 return task_work_cancel_match(task, task_work_func_match, func);
121 }
122
123 /**
124 * task_work_run - execute the works added by task_work_add()
125 *
126 * Flush the pending works. Should be used by the core kernel code.
127 * Called before the task returns to the user-mode or stops, or when
128 * it exits. In the latter case task_work_add() can no longer add the
129 * new work after task_work_run() returns.
130 */
task_work_run(void)131 void task_work_run(void)
132 {
133 struct task_struct *task = current;
134 struct callback_head *work, *head, *next;
135
136 for (;;) {
137 /*
138 * work->func() can do task_work_add(), do not set
139 * work_exited unless the list is empty.
140 */
141 do {
142 head = NULL;
143 work = READ_ONCE(task->task_works);
144 if (!work) {
145 if (task->flags & PF_EXITING)
146 head = &work_exited;
147 else
148 break;
149 }
150 } while (cmpxchg(&task->task_works, work, head) != work);
151
152 if (!work)
153 break;
154 /*
155 * Synchronize with task_work_cancel(). It can not remove
156 * the first entry == work, cmpxchg(task_works) must fail.
157 * But it can remove another entry from the ->next list.
158 */
159 raw_spin_lock_irq(&task->pi_lock);
160 raw_spin_unlock_irq(&task->pi_lock);
161
162 do {
163 next = work->next;
164 work->func(work);
165 work = next;
166 cond_resched();
167 } while (work);
168 }
169 }
170
