1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/irq_work.h>
3 #include <linux/spinlock.h>
4 #include <linux/task_work.h>
5 #include <linux/resume_user_mode.h>
6
7 static struct callback_head work_exited; /* all we need is ->next == NULL */
8
9 #ifdef CONFIG_IRQ_WORK
10 static void task_work_set_notify_irq(struct irq_work *entry)
11 {
12 test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
13 }
14 static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
15 IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
16 #endif
17
18 /**
19 * task_work_add - ask the @task to execute @work->func()
20 * @task: the task which should run the callback
21 * @work: the callback to run
22 * @notify: how to notify the targeted task
23 *
24 * Queue @work for task_work_run() below and notify the @task if @notify
25 * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
26 *
27 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
28 * task and run the task_work, regardless of whether the task is currently
29 * running in the kernel or userspace.
30 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a
31 * reschedule IPI to force the targeted task to reschedule and run task_work.
32 * This can be advantageous if there's no strict requirement that the
33 * task_work be run as soon as possible, just whenever the task enters the
34 * kernel anyway.
35 * @TWA_RESUME work is run only when the task exits the kernel and returns to
36 * user mode, or before entering guest mode.
37 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
38 * current @task and if the current context is NMI.
39 *
40 * Fails if the @task is exiting/exited and thus it can't process this @work.
41 * Otherwise @work->func() will be called when the @task goes through one of
42 * the aforementioned transitions, or exits.
43 *
44 * If the targeted task is exiting, then an error is returned and the work item
45 * is not queued. It's up to the caller to arrange for an alternative mechanism
46 * in that case.
47 *
48 * Note: there is no ordering guarantee on works queued here. The task_work
49 * list is LIFO.
50 *
51 * RETURNS:
52 * 0 if succeeds or -ESRCH.
53 */
54 int task_work_add(struct task_struct *task, struct callback_head *work,
55 enum task_work_notify_mode notify)
56 {
57 struct callback_head *head;
58
59 if (notify == TWA_NMI_CURRENT) {
60 if (WARN_ON_ONCE(task != current))
61 return -EINVAL;
62 if (!IS_ENABLED(CONFIG_IRQ_WORK))
63 return -EINVAL;
64 } else {
65 /* record the work call stack in order to print it in KASAN reports */
66 kasan_record_aux_stack(work);
67 }
68
69 head = READ_ONCE(task->task_works);
70 do {
71 if (unlikely(head == &work_exited))
72 return -ESRCH;
73 work->next = head;
74 } while (!try_cmpxchg(&task->task_works, &head, work));
75
76 switch (notify) {
77 case TWA_NONE:
78 break;
79 case TWA_RESUME:
80 set_notify_resume(task);
81 break;
82 case TWA_SIGNAL:
83 set_notify_signal(task);
84 break;
85 case TWA_SIGNAL_NO_IPI:
86 __set_notify_signal(task);
87 break;
88 #ifdef CONFIG_IRQ_WORK
89 case TWA_NMI_CURRENT:
90 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
91 break;
92 #endif
93 default:
94 WARN_ON_ONCE(1);
95 break;
96 }
97
98 return 0;
99 }
100
101 /**
102 * task_work_cancel_match - cancel a pending work added by task_work_add()
103 * @task: the task which should execute the work
104 * @match: match function to call
105 * @data: data to be passed in to match function
106 *
107 * RETURNS:
108 * The found work or NULL if not found.
109 */
110 struct callback_head *
111 task_work_cancel_match(struct task_struct *task,
112 bool (*match)(struct callback_head *, void *data),
113 void *data)
114 {
115 struct callback_head **pprev = &task->task_works;
116 struct callback_head *work;
117 unsigned long flags;
118
119 if (likely(!task_work_pending(task)))
120 return NULL;
121 /*
122 * If cmpxchg() fails we continue without updating pprev.
123 * Either we raced with task_work_add() which added the
124 * new entry before this work, we will find it again. Or
125 * we raced with task_work_run(), *pprev == NULL/exited.
126 */
127 raw_spin_lock_irqsave(&task->pi_lock, flags);
128 work = READ_ONCE(*pprev);
129 while (work) {
130 if (!match(work, data)) {
131 pprev = &work->next;
132 work = READ_ONCE(*pprev);
133 } else if (try_cmpxchg(pprev, &work, work->next))
134 break;
135 }
136 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
137
138 return work;
139 }
140
141 static bool task_work_func_match(struct callback_head *cb, void *data)
142 {
143 return cb->func == data;
144 }
145
146 /**
147 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add()
148 * @task: the task which should execute the func's work
149 * @func: identifies the func to match with a work to remove
150 *
151 * Find the last queued pending work with ->func == @func and remove
152 * it from queue.
153 *
154 * RETURNS:
155 * The found work or NULL if not found.
156 */
157 struct callback_head *
158 task_work_cancel_func(struct task_struct *task, task_work_func_t func)
159 {
160 return task_work_cancel_match(task, task_work_func_match, func);
161 }
162
163 static bool task_work_match(struct callback_head *cb, void *data)
164 {
165 return cb == data;
166 }
167
168 /**
169 * task_work_cancel - cancel a pending work added by task_work_add()
170 * @task: the task which should execute the work
171 * @cb: the callback to remove if queued
172 *
173 * Remove a callback from a task's queue if queued.
174 *
175 * RETURNS:
176 * True if the callback was queued and got cancelled, false otherwise.
177 */
178 bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
179 {
180 struct callback_head *ret;
181
182 ret = task_work_cancel_match(task, task_work_match, cb);
183
184 return ret == cb;
185 }
186
187 /**
188 * task_work_run - execute the works added by task_work_add()
189 *
190 * Flush the pending works. Should be used by the core kernel code.
191 * Called before the task returns to the user-mode or stops, or when
192 * it exits. In the latter case task_work_add() can no longer add the
193 * new work after task_work_run() returns.
194 */
195 void task_work_run(void)
196 {
197 struct task_struct *task = current;
198 struct callback_head *work, *head, *next;
199
200 for (;;) {
201 /*
202 * work->func() can do task_work_add(), do not set
203 * work_exited unless the list is empty.
204 */
205 work = READ_ONCE(task->task_works);
206 do {
207 head = NULL;
208 if (!work) {
209 if (task->flags & PF_EXITING)
210 head = &work_exited;
211 else
212 break;
213 }
214 } while (!try_cmpxchg(&task->task_works, &work, head));
215
216 if (!work)
217 break;
218 /*
219 * Synchronize with task_work_cancel_match(). It can not remove
220 * the first entry == work, cmpxchg(task_works) must fail.
221 * But it can remove another entry from the ->next list.
222 */
223 raw_spin_lock_irq(&task->pi_lock);
224 raw_spin_unlock_irq(&task->pi_lock);
225
226 do {
227 next = work->next;
228 work->func(work);
229 work = next;
230 cond_resched();
231 } while (work);
232 }
233 }
234
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