| 1 | |
| 2 | #include <linux/spinlock.h>
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| 3 | #include <linux/task_work.h>
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| 4 | #include <linux/tracehook.h>
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| 5 |
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| 6 | static struct callback_head work_exited;
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| 7 |
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| 8 | |
| 9 | * task_work_add - ask the @task to execute @work->func()
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| 10 | * @task: the task which should run the callback
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| 11 | * @work: the callback to run
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| 12 | * @notify: send the notification if true
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| 13 | *
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| 14 | * Queue @work for task_work_run() below and notify the @task if @notify.
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| 15 | * Fails if the @task is exiting/exited and thus it can't process this @work.
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| 16 | * Otherwise @work->func() will be called when the @task returns from kernel
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| 17 | * mode or exits.
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| 18 | *
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| 19 | * This is like the signal handler which runs in kernel mode, but it doesn't
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| 20 | * try to wake up the @task.
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| 21 | *
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| 22 | * Note: there is no ordering guarantee on works queued here.
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| 23 | *
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| 24 | * RETURNS:
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| 25 | * 0 if succeeds or -ESRCH.
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| 26 |
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| 27 | int
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| 28 | task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
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| 29 | {
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| 30 | struct callback_head *head;
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| 31 |
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| 32 | do {
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| 33 | head = READ_ONCE(task->task_works);
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| 34 | if (unlikely(head == &work_exited))
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| 35 | return -ESRCH;
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| 36 | work->next = head;
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| 37 | } while (cmpxchg(&task->task_works, head, work) != head);
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| 38 |
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| 39 | if (notify)
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| 40 | set_notify_resume(task);
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| 41 | return 0;
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| 42 | }
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| 43 |
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| 44 | |
| 45 | * task_work_cancel - cancel a pending work added by task_work_add()
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| 46 | * @task: the task which should execute the work
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| 47 | * @func: identifies the work to remove
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| 48 | *
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| 49 | * Find the last queued pending work with ->func == @func and remove
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| 50 | * it from queue.
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| 51 | *
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| 52 | * RETURNS:
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| 53 | * The found work or NULL if not found.
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| 54 |
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| 55 | struct callback_head *
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| 56 | task_work_cancel(struct task_struct *task, task_work_func_t func)
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| 57 | {
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| 58 | struct callback_head **pprev = &task->task_works;
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| 59 | struct callback_head *work;
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| 60 | unsigned long flags;
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| 61 |
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| 62 | if (likely(!task->task_works))
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| 63 | return NULL;
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| 64 | |
| 65 | * If cmpxchg() fails we continue without updating pprev.
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| 66 | * Either we raced with task_work_add() which added the
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| 67 | * new entry before this work, we will find it again. Or
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| 68 | * we raced with task_work_run(), *pprev == NULL/exited.
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| 69 |
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| 70 | raw_spin_lock_irqsave(&task->pi_lock, flags);
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| 71 | while ((work = READ_ONCE(*pprev))) {
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| 72 | if (work->func != func)
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| 73 | pprev = &work->next;
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| 74 | else if (cmpxchg(pprev, work, work->next) == work)
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| 75 | break;
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| 76 | }
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| 77 | raw_spin_unlock_irqrestore(&task->pi_lock, flags);
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| 78 |
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| 79 | return work;
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| 80 | }
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| 81 |
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| 82 | |
| 83 | * task_work_run - execute the works added by task_work_add()
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| 84 | *
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| 85 | * Flush the pending works. Should be used by the core kernel code.
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| 86 | * Called before the task returns to the user-mode or stops, or when
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| 87 | * it exits. In the latter case task_work_add() can no longer add the
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| 88 | * new work after task_work_run() returns.
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| 89 |
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| 90 | void task_work_run(void)
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| 91 | {
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| 92 | struct task_struct *task = current;
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| 93 | struct callback_head *work, *head, *next;
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| 94 |
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| 95 | for (;;) {
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| 96 | |
| 97 | * work->func() can do task_work_add(), do not set
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| 98 | * work_exited unless the list is empty.
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| 99 |
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| 100 | raw_spin_lock_irq(&task->pi_lock);
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| 101 | do {
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| 102 | work = READ_ONCE(task->task_works);
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| 103 | head = !work && (task->flags & PF_EXITING) ?
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| 104 | &work_exited : NULL;
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| 105 | } while (cmpxchg(&task->task_works, work, head) != work);
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| 106 | raw_spin_unlock_irq(&task->pi_lock);
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| 107 |
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| 108 | if (!work)
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| 109 | break;
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| 110 |
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| 111 | do {
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| 112 | next = work->next;
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| 113 | work->func(work);
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| 114 | work = next;
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| 115 | cond_resched();
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| 116 | } while (work);
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| 117 | }
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| 118 | }
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