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1#include <linux/spinlock.h>
2#include <linux/task_work.h>
3#include <linux/tracehook.h>
4
5static struct callback_head work_exited; /* all we need is ->next == NULL */
6
7/**
8 * task_work_add - ask the @task to execute @work->func()
9 * @task: the task which should run the callback
10 * @work: the callback to run
11 * @notify: send the notification if true
12 *
13 * Queue @work for task_work_run() below and notify the @task if @notify.
14 * Fails if the @task is exiting/exited and thus it can't process this @work.
15 * Otherwise @work->func() will be called when the @task returns from kernel
16 * mode or exits.
17 *
18 * This is like the signal handler which runs in kernel mode, but it doesn't
19 * try to wake up the @task.
20 *
21 * RETURNS:
22 * 0 if succeeds or -ESRCH.
23 */
24int
25task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
26{
27 struct callback_head *head;
28
29 do {
30 head = ACCESS_ONCE(task->task_works);
31 if (unlikely(head == &work_exited))
32 return -ESRCH;
33 work->next = head;
34 } while (cmpxchg(&task->task_works, head, work) != head);
35
36 if (notify)
37 set_notify_resume(task);
38 return 0;
39}
40
41/**
42 * task_work_cancel - cancel a pending work added by task_work_add()
43 * @task: the task which should execute the work
44 * @func: identifies the work to remove
45 *
46 * Find the last queued pending work with ->func == @func and remove
47 * it from queue.
48 *
49 * RETURNS:
50 * The found work or NULL if not found.
51 */
52struct callback_head *
53task_work_cancel(struct task_struct *task, task_work_func_t func)
54{
55 struct callback_head **pprev = &task->task_works;
56 struct callback_head *work;
57 unsigned long flags;
58 /*
59 * If cmpxchg() fails we continue without updating pprev.
60 * Either we raced with task_work_add() which added the
61 * new entry before this work, we will find it again. Or
62 * we raced with task_work_run(), *pprev == NULL/exited.
63 */
64 raw_spin_lock_irqsave(&task->pi_lock, flags);
65 while ((work = ACCESS_ONCE(*pprev))) {
66 smp_read_barrier_depends();
67 if (work->func != func)
68 pprev = &work->next;
69 else if (cmpxchg(pprev, work, work->next) == work)
70 break;
71 }
72 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
73
74 return work;
75}
76
77/**
78 * task_work_run - execute the works added by task_work_add()
79 *
80 * Flush the pending works. Should be used by the core kernel code.
81 * Called before the task returns to the user-mode or stops, or when
82 * it exits. In the latter case task_work_add() can no longer add the
83 * new work after task_work_run() returns.
84 */
85void task_work_run(void)
86{
87 struct task_struct *task = current;
88 struct callback_head *work, *head, *next;
89
90 for (;;) {
91 /*
92 * work->func() can do task_work_add(), do not set
93 * work_exited unless the list is empty.
94 */
95 do {
96 work = ACCESS_ONCE(task->task_works);
97 head = !work && (task->flags & PF_EXITING) ?
98 &work_exited : NULL;
99 } while (cmpxchg(&task->task_works, work, head) != work);
100
101 if (!work)
102 break;
103 /*
104 * Synchronize with task_work_cancel(). It can't remove
105 * the first entry == work, cmpxchg(task_works) should
106 * fail, but it can play with *work and other entries.
107 */
108 raw_spin_unlock_wait(&task->pi_lock);
109 smp_mb();
110
111 /* Reverse the list to run the works in fifo order */
112 head = NULL;
113 do {
114 next = work->next;
115 work->next = head;
116 head = work;
117 work = next;
118 } while (work);
119
120 work = head;
121 do {
122 next = work->next;
123 work->func(work);
124 work = next;
125 cond_resched();
126 } while (work);
127 }
128}
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
7static struct callback_head work_exited; /* all we need is ->next == NULL */
8
9#ifdef CONFIG_IRQ_WORK
10static void task_work_set_notify_irq(struct irq_work *entry)
11{
12 test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
13}
14static 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 */
54int 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
112/**
113 * task_work_cancel_match - cancel a pending work added by task_work_add()
114 * @task: the task which should execute the work
115 * @match: match function to call
116 * @data: data to be passed in to match function
117 *
118 * RETURNS:
119 * The found work or NULL if not found.
120 */
121struct callback_head *
122task_work_cancel_match(struct task_struct *task,
123 bool (*match)(struct callback_head *, void *data),
124 void *data)
125{
126 struct callback_head **pprev = &task->task_works;
127 struct callback_head *work;
128 unsigned long flags;
129
130 if (likely(!task_work_pending(task)))
131 return NULL;
132 /*
133 * If cmpxchg() fails we continue without updating pprev.
134 * Either we raced with task_work_add() which added the
135 * new entry before this work, we will find it again. Or
136 * we raced with task_work_run(), *pprev == NULL/exited.
137 */
138 raw_spin_lock_irqsave(&task->pi_lock, flags);
139 work = READ_ONCE(*pprev);
140 while (work) {
141 if (!match(work, data)) {
142 pprev = &work->next;
143 work = READ_ONCE(*pprev);
144 } else if (try_cmpxchg(pprev, &work, work->next))
145 break;
146 }
147 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
148
149 return work;
150}
151
152static bool task_work_func_match(struct callback_head *cb, void *data)
153{
154 return cb->func == data;
155}
156
157/**
158 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add()
159 * @task: the task which should execute the func's work
160 * @func: identifies the func to match with a work to remove
161 *
162 * Find the last queued pending work with ->func == @func and remove
163 * it from queue.
164 *
165 * RETURNS:
166 * The found work or NULL if not found.
167 */
168struct callback_head *
169task_work_cancel_func(struct task_struct *task, task_work_func_t func)
170{
171 return task_work_cancel_match(task, task_work_func_match, func);
172}
173
174static bool task_work_match(struct callback_head *cb, void *data)
175{
176 return cb == data;
177}
178
179/**
180 * task_work_cancel - cancel a pending work added by task_work_add()
181 * @task: the task which should execute the work
182 * @cb: the callback to remove if queued
183 *
184 * Remove a callback from a task's queue if queued.
185 *
186 * RETURNS:
187 * True if the callback was queued and got cancelled, false otherwise.
188 */
189bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
190{
191 struct callback_head *ret;
192
193 ret = task_work_cancel_match(task, task_work_match, cb);
194
195 return ret == cb;
196}
197
198/**
199 * task_work_run - execute the works added by task_work_add()
200 *
201 * Flush the pending works. Should be used by the core kernel code.
202 * Called before the task returns to the user-mode or stops, or when
203 * it exits. In the latter case task_work_add() can no longer add the
204 * new work after task_work_run() returns.
205 */
206void task_work_run(void)
207{
208 struct task_struct *task = current;
209 struct callback_head *work, *head, *next;
210
211 for (;;) {
212 /*
213 * work->func() can do task_work_add(), do not set
214 * work_exited unless the list is empty.
215 */
216 work = READ_ONCE(task->task_works);
217 do {
218 head = NULL;
219 if (!work) {
220 if (task->flags & PF_EXITING)
221 head = &work_exited;
222 else
223 break;
224 }
225 } while (!try_cmpxchg(&task->task_works, &work, head));
226
227 if (!work)
228 break;
229 /*
230 * Synchronize with task_work_cancel_match(). It can not remove
231 * the first entry == work, cmpxchg(task_works) must fail.
232 * But it can remove another entry from the ->next list.
233 */
234 raw_spin_lock_irq(&task->pi_lock);
235 raw_spin_unlock_irq(&task->pi_lock);
236
237 do {
238 next = work->next;
239 work->func(work);
240 work = next;
241 cond_resched();
242 } while (work);
243 }
244}