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 unsigned long flags;
37
38 do {
39 head = READ_ONCE(task->task_works);
40 if (unlikely(head == &work_exited))
41 return -ESRCH;
42 work->next = head;
43 } while (cmpxchg(&task->task_works, head, work) != head);
44
45 switch (notify) {
46 case TWA_NONE:
47 break;
48 case TWA_RESUME:
49 set_notify_resume(task);
50 break;
51 case TWA_SIGNAL:
52 /*
53 * Only grab the sighand lock if we don't already have some
54 * task_work pending. This pairs with the smp_store_mb()
55 * in get_signal(), see comment there.
56 */
57 if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
58 lock_task_sighand(task, &flags)) {
59 task->jobctl |= JOBCTL_TASK_WORK;
60 signal_wake_up(task, 0);
61 unlock_task_sighand(task, &flags);
62 }
63 break;
64 default:
65 WARN_ON_ONCE(1);
66 break;
67 }
68
69 return 0;
70 }
71
72 /**
73 * task_work_cancel - cancel a pending work added by task_work_add()
74 * @task: the task which should execute the work
75 * @func: identifies the work to remove
76 *
77 * Find the last queued pending work with ->func == @func and remove
78 * it from queue.
79 *
80 * RETURNS:
81 * The found work or NULL if not found.
82 */
83 struct callback_head *
task_work_cancel(struct task_struct * task,task_work_func_t func)84 task_work_cancel(struct task_struct *task, task_work_func_t func)
85 {
86 struct callback_head **pprev = &task->task_works;
87 struct callback_head *work;
88 unsigned long flags;
89
90 if (likely(!task->task_works))
91 return NULL;
92 /*
93 * If cmpxchg() fails we continue without updating pprev.
94 * Either we raced with task_work_add() which added the
95 * new entry before this work, we will find it again. Or
96 * we raced with task_work_run(), *pprev == NULL/exited.
97 */
98 raw_spin_lock_irqsave(&task->pi_lock, flags);
99 while ((work = READ_ONCE(*pprev))) {
100 if (work->func != func)
101 pprev = &work->next;
102 else if (cmpxchg(pprev, work, work->next) == work)
103 break;
104 }
105 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
106
107 return work;
108 }
109
110 /**
111 * task_work_run - execute the works added by task_work_add()
112 *
113 * Flush the pending works. Should be used by the core kernel code.
114 * Called before the task returns to the user-mode or stops, or when
115 * it exits. In the latter case task_work_add() can no longer add the
116 * new work after task_work_run() returns.
117 */
task_work_run(void)118 void task_work_run(void)
119 {
120 struct task_struct *task = current;
121 struct callback_head *work, *head, *next;
122
123 for (;;) {
124 /*
125 * work->func() can do task_work_add(), do not set
126 * work_exited unless the list is empty.
127 */
128 do {
129 head = NULL;
130 work = READ_ONCE(task->task_works);
131 if (!work) {
132 if (task->flags & PF_EXITING)
133 head = &work_exited;
134 else
135 break;
136 }
137 } while (cmpxchg(&task->task_works, work, head) != work);
138
139 if (!work)
140 break;
141 /*
142 * Synchronize with task_work_cancel(). It can not remove
143 * the first entry == work, cmpxchg(task_works) must fail.
144 * But it can remove another entry from the ->next list.
145 */
146 raw_spin_lock_irq(&task->pi_lock);
147 raw_spin_unlock_irq(&task->pi_lock);
148
149 do {
150 next = work->next;
151 work->func(work);
152 work = next;
153 cond_resched();
154 } while (work);
155 }
156 }
157
