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1 | #include <linux/spinlock.h> | |
2 | #include <linux/task_work.h> | |
3 | #include <linux/tracehook.h> | |
4 | ||
5 | static 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 | * Note: there is no ordering guarantee on works queued here. | |
22 | * | |
23 | * RETURNS: | |
24 | * 0 if succeeds or -ESRCH. | |
25 | */ | |
26 | int | |
27 | task_work_add(struct task_struct *task, struct callback_head *work, bool notify) | |
28 | { | |
29 | struct callback_head *head; | |
30 | ||
31 | do { | |
32 | head = READ_ONCE(task->task_works); | |
33 | if (unlikely(head == &work_exited)) | |
34 | return -ESRCH; | |
35 | work->next = head; | |
36 | } while (cmpxchg(&task->task_works, head, work) != head); | |
37 | ||
38 | if (notify) | |
39 | set_notify_resume(task); | |
40 | return 0; | |
41 | } | |
42 | ||
43 | /** | |
44 | * task_work_cancel - cancel a pending work added by task_work_add() | |
45 | * @task: the task which should execute the work | |
46 | * @func: identifies the work to remove | |
47 | * | |
48 | * Find the last queued pending work with ->func == @func and remove | |
49 | * it from queue. | |
50 | * | |
51 | * RETURNS: | |
52 | * The found work or NULL if not found. | |
53 | */ | |
54 | struct callback_head * | |
55 | task_work_cancel(struct task_struct *task, task_work_func_t func) | |
56 | { | |
57 | struct callback_head **pprev = &task->task_works; | |
58 | struct callback_head *work; | |
59 | unsigned long flags; | |
60 | ||
61 | if (likely(!task->task_works)) | |
62 | return NULL; | |
63 | /* | |
64 | * If cmpxchg() fails we continue without updating pprev. | |
65 | * Either we raced with task_work_add() which added the | |
66 | * new entry before this work, we will find it again. Or | |
67 | * we raced with task_work_run(), *pprev == NULL/exited. | |
68 | */ | |
69 | raw_spin_lock_irqsave(&task->pi_lock, flags); | |
70 | while ((work = lockless_dereference(*pprev))) { | |
71 | if (work->func != func) | |
72 | pprev = &work->next; | |
73 | else if (cmpxchg(pprev, work, work->next) == work) | |
74 | break; | |
75 | } | |
76 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); | |
77 | ||
78 | return work; | |
79 | } | |
80 | ||
81 | /** | |
82 | * task_work_run - execute the works added by task_work_add() | |
83 | * | |
84 | * Flush the pending works. Should be used by the core kernel code. | |
85 | * Called before the task returns to the user-mode or stops, or when | |
86 | * it exits. In the latter case task_work_add() can no longer add the | |
87 | * new work after task_work_run() returns. | |
88 | */ | |
89 | void task_work_run(void) | |
90 | { | |
91 | struct task_struct *task = current; | |
92 | struct callback_head *work, *head, *next; | |
93 | ||
94 | for (;;) { | |
95 | /* | |
96 | * work->func() can do task_work_add(), do not set | |
97 | * work_exited unless the list is empty. | |
98 | */ | |
99 | do { | |
100 | work = READ_ONCE(task->task_works); | |
101 | head = !work && (task->flags & PF_EXITING) ? | |
102 | &work_exited : NULL; | |
103 | } while (cmpxchg(&task->task_works, work, head) != work); | |
104 | ||
105 | if (!work) | |
106 | break; | |
107 | /* | |
108 | * Synchronize with task_work_cancel(). It can't remove | |
109 | * the first entry == work, cmpxchg(task_works) should | |
110 | * fail, but it can play with *work and other entries. | |
111 | */ | |
112 | raw_spin_unlock_wait(&task->pi_lock); | |
113 | ||
114 | do { | |
115 | next = work->next; | |
116 | work->func(work); | |
117 | work = next; | |
118 | cond_resched(); | |
119 | } while (work); | |
120 | } | |
121 | } |