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
task_work_set_notify_irq(struct irq_work * entry)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 */
task_work_add(struct task_struct * task,struct callback_head * work,enum task_work_notify_mode notify)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 int flags = notify & TWA_FLAGS;
59
60 notify &= ~TWA_FLAGS;
61 if (notify == TWA_NMI_CURRENT) {
62 if (WARN_ON_ONCE(task != current))
63 return -EINVAL;
64 if (!IS_ENABLED(CONFIG_IRQ_WORK))
65 return -EINVAL;
66 } else {
67 /*
68 * Record the work call stack in order to print it in KASAN
69 * reports.
70 *
71 * Note that stack allocation can fail if TWAF_NO_ALLOC flag
72 * is set and new page is needed to expand the stack buffer.
73 */
74 if (flags & TWAF_NO_ALLOC)
75 kasan_record_aux_stack_noalloc(work);
76 else
77 kasan_record_aux_stack(work);
78 }
79
80 head = READ_ONCE(task->task_works);
81 do {
82 if (unlikely(head == &work_exited))
83 return -ESRCH;
84 work->next = head;
85 } while (!try_cmpxchg(&task->task_works, &head, work));
86
87 switch (notify) {
88 case TWA_NONE:
89 break;
90 case TWA_RESUME:
91 set_notify_resume(task);
92 break;
93 case TWA_SIGNAL:
94 set_notify_signal(task);
95 break;
96 case TWA_SIGNAL_NO_IPI:
97 __set_notify_signal(task);
98 break;
99 #ifdef CONFIG_IRQ_WORK
100 case TWA_NMI_CURRENT:
101 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
102 break;
103 #endif
104 default:
105 WARN_ON_ONCE(1);
106 break;
107 }
108
109 return 0;
110 }
111 EXPORT_SYMBOL_GPL(task_work_add);
112
113 /**
114 * task_work_cancel_match - cancel a pending work added by task_work_add()
115 * @task: the task which should execute the work
116 * @match: match function to call
117 * @data: data to be passed in to match function
118 *
119 * RETURNS:
120 * The found work or NULL if not found.
121 */
122 struct callback_head *
task_work_cancel_match(struct task_struct * task,bool (* match)(struct callback_head *,void * data),void * data)123 task_work_cancel_match(struct task_struct *task,
124 bool (*match)(struct callback_head *, void *data),
125 void *data)
126 {
127 struct callback_head **pprev = &task->task_works;
128 struct callback_head *work;
129 unsigned long flags;
130
131 if (likely(!task_work_pending(task)))
132 return NULL;
133 /*
134 * If cmpxchg() fails we continue without updating pprev.
135 * Either we raced with task_work_add() which added the
136 * new entry before this work, we will find it again. Or
137 * we raced with task_work_run(), *pprev == NULL/exited.
138 */
139 raw_spin_lock_irqsave(&task->pi_lock, flags);
140 work = READ_ONCE(*pprev);
141 while (work) {
142 if (!match(work, data)) {
143 pprev = &work->next;
144 work = READ_ONCE(*pprev);
145 } else if (try_cmpxchg(pprev, &work, work->next))
146 break;
147 }
148 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
149
150 return work;
151 }
152
task_work_func_match(struct callback_head * cb,void * data)153 static bool task_work_func_match(struct callback_head *cb, void *data)
154 {
155 return cb->func == data;
156 }
157
158 /**
159 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add()
160 * @task: the task which should execute the func's work
161 * @func: identifies the func to match with a work to remove
162 *
163 * Find the last queued pending work with ->func == @func and remove
164 * it from queue.
165 *
166 * RETURNS:
167 * The found work or NULL if not found.
168 */
169 struct callback_head *
task_work_cancel_func(struct task_struct * task,task_work_func_t func)170 task_work_cancel_func(struct task_struct *task, task_work_func_t func)
171 {
172 return task_work_cancel_match(task, task_work_func_match, func);
173 }
174
task_work_match(struct callback_head * cb,void * data)175 static bool task_work_match(struct callback_head *cb, void *data)
176 {
177 return cb == data;
178 }
179
180 /**
181 * task_work_cancel - cancel a pending work added by task_work_add()
182 * @task: the task which should execute the work
183 * @cb: the callback to remove if queued
184 *
185 * Remove a callback from a task's queue if queued.
186 *
187 * RETURNS:
188 * True if the callback was queued and got cancelled, false otherwise.
189 */
task_work_cancel(struct task_struct * task,struct callback_head * cb)190 bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
191 {
192 struct callback_head *ret;
193
194 ret = task_work_cancel_match(task, task_work_match, cb);
195
196 return ret == cb;
197 }
198
199 /**
200 * task_work_run - execute the works added by task_work_add()
201 *
202 * Flush the pending works. Should be used by the core kernel code.
203 * Called before the task returns to the user-mode or stops, or when
204 * it exits. In the latter case task_work_add() can no longer add the
205 * new work after task_work_run() returns.
206 */
task_work_run(void)207 void task_work_run(void)
208 {
209 struct task_struct *task = current;
210 struct callback_head *work, *head, *next;
211
212 for (;;) {
213 /*
214 * work->func() can do task_work_add(), do not set
215 * work_exited unless the list is empty.
216 */
217 work = READ_ONCE(task->task_works);
218 do {
219 head = NULL;
220 if (!work) {
221 if (task->flags & PF_EXITING)
222 head = &work_exited;
223 else
224 break;
225 }
226 } while (!try_cmpxchg(&task->task_works, &work, head));
227
228 if (!work)
229 break;
230 /*
231 * Synchronize with task_work_cancel_match(). It can not remove
232 * the first entry == work, cmpxchg(task_works) must fail.
233 * But it can remove another entry from the ->next list.
234 */
235 raw_spin_lock_irq(&task->pi_lock);
236 raw_spin_unlock_irq(&task->pi_lock);
237
238 do {
239 next = work->next;
240 work->func(work);
241 work = next;
242 cond_resched();
243 } while (work);
244 }
245 }
246