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
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, @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 */
task_work_add(struct task_struct * task,struct callback_head * work,enum task_work_notify_mode notify)42 int 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 */
85 struct callback_head *
task_work_cancel_match(struct task_struct * task,bool (* match)(struct callback_head *,void * data),void * data)86 task_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
task_work_func_match(struct callback_head * cb,void * data)116 static 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 */
132 struct callback_head *
task_work_cancel(struct task_struct * task,task_work_func_t func)133 task_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 */
task_work_run(void)146 void 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 }
185