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 * @data: data to be passed in to match function
82 *
83 * RETURNS:
84 * The found work or NULL if not found.
85 */
86 struct callback_head *
task_work_cancel_match(struct task_struct * task,bool (* match)(struct callback_head *,void * data),void * data)87 task_work_cancel_match(struct task_struct *task,
88 bool (*match)(struct callback_head *, void *data),
89 void *data)
90 {
91 struct callback_head **pprev = &task->task_works;
92 struct callback_head *work;
93 unsigned long flags;
94
95 if (likely(!task_work_pending(task)))
96 return NULL;
97 /*
98 * If cmpxchg() fails we continue without updating pprev.
99 * Either we raced with task_work_add() which added the
100 * new entry before this work, we will find it again. Or
101 * we raced with task_work_run(), *pprev == NULL/exited.
102 */
103 raw_spin_lock_irqsave(&task->pi_lock, flags);
104 work = READ_ONCE(*pprev);
105 while (work) {
106 if (!match(work, data)) {
107 pprev = &work->next;
108 work = READ_ONCE(*pprev);
109 } else if (try_cmpxchg(pprev, &work, work->next))
110 break;
111 }
112 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
113
114 return work;
115 }
116
task_work_func_match(struct callback_head * cb,void * data)117 static bool task_work_func_match(struct callback_head *cb, void *data)
118 {
119 return cb->func == data;
120 }
121
122 /**
123 * task_work_cancel - cancel a pending work added by task_work_add()
124 * @task: the task which should execute the work
125 * @func: identifies the work to remove
126 *
127 * Find the last queued pending work with ->func == @func and remove
128 * it from queue.
129 *
130 * RETURNS:
131 * The found work or NULL if not found.
132 */
133 struct callback_head *
task_work_cancel(struct task_struct * task,task_work_func_t func)134 task_work_cancel(struct task_struct *task, task_work_func_t func)
135 {
136 return task_work_cancel_match(task, task_work_func_match, func);
137 }
138
139 /**
140 * task_work_run - execute the works added by task_work_add()
141 *
142 * Flush the pending works. Should be used by the core kernel code.
143 * Called before the task returns to the user-mode or stops, or when
144 * it exits. In the latter case task_work_add() can no longer add the
145 * new work after task_work_run() returns.
146 */
task_work_run(void)147 void task_work_run(void)
148 {
149 struct task_struct *task = current;
150 struct callback_head *work, *head, *next;
151
152 for (;;) {
153 /*
154 * work->func() can do task_work_add(), do not set
155 * work_exited unless the list is empty.
156 */
157 work = READ_ONCE(task->task_works);
158 do {
159 head = NULL;
160 if (!work) {
161 if (task->flags & PF_EXITING)
162 head = &work_exited;
163 else
164 break;
165 }
166 } while (!try_cmpxchg(&task->task_works, &work, head));
167
168 if (!work)
169 break;
170 /*
171 * Synchronize with task_work_cancel(). It can not remove
172 * the first entry == work, cmpxchg(task_works) must fail.
173 * But it can remove another entry from the ->next list.
174 */
175 raw_spin_lock_irq(&task->pi_lock);
176 raw_spin_unlock_irq(&task->pi_lock);
177
178 do {
179 next = work->next;
180 work->func(work);
181 work = next;
182 cond_resched();
183 } while (work);
184 }
185 }
186