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TOMOYO Linux Cross Reference
Linux/kernel/task_work.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 #include <linux/spinlock.h>
  3 #include <linux/task_work.h>
  4 #include <linux/tracehook.h>
  5 
  6 static struct callback_head work_exited; /* all we need is ->next == NULL */
  7 
  8 /**
  9  * task_work_add - ask the @task to execute @work->func()
 10  * @task: the task which should run the callback
 11  * @work: the callback to run
 12  * @notify: send the notification if true
 13  *
 14  * Queue @work for task_work_run() below and notify the @task if @notify.
 15  * Fails if the @task is exiting/exited and thus it can't process this @work.
 16  * Otherwise @work->func() will be called when the @task returns from kernel
 17  * mode or exits.
 18  *
 19  * This is like the signal handler which runs in kernel mode, but it doesn't
 20  * try to wake up the @task.
 21  *
 22  * Note: there is no ordering guarantee on works queued here.
 23  *
 24  * RETURNS:
 25  * 0 if succeeds or -ESRCH.
 26  */
 27 int
 28 task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
 29 {
 30         struct callback_head *head;
 31 
 32         do {
 33                 head = READ_ONCE(task->task_works);
 34                 if (unlikely(head == &work_exited))
 35                         return -ESRCH;
 36                 work->next = head;
 37         } while (cmpxchg(&task->task_works, head, work) != head);
 38 
 39         if (notify)
 40                 set_notify_resume(task);
 41         return 0;
 42 }
 43 
 44 /**
 45  * task_work_cancel - cancel a pending work added by task_work_add()
 46  * @task: the task which should execute the work
 47  * @func: identifies the work to remove
 48  *
 49  * Find the last queued pending work with ->func == @func and remove
 50  * it from queue.
 51  *
 52  * RETURNS:
 53  * The found work or NULL if not found.
 54  */
 55 struct callback_head *
 56 task_work_cancel(struct task_struct *task, task_work_func_t func)
 57 {
 58         struct callback_head **pprev = &task->task_works;
 59         struct callback_head *work;
 60         unsigned long flags;
 61 
 62         if (likely(!task->task_works))
 63                 return NULL;
 64         /*
 65          * If cmpxchg() fails we continue without updating pprev.
 66          * Either we raced with task_work_add() which added the
 67          * new entry before this work, we will find it again. Or
 68          * we raced with task_work_run(), *pprev == NULL/exited.
 69          */
 70         raw_spin_lock_irqsave(&task->pi_lock, flags);
 71         while ((work = READ_ONCE(*pprev))) {
 72                 if (work->func != func)
 73                         pprev = &work->next;
 74                 else if (cmpxchg(pprev, work, work->next) == work)
 75                         break;
 76         }
 77         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 78 
 79         return work;
 80 }
 81 
 82 /**
 83  * task_work_run - execute the works added by task_work_add()
 84  *
 85  * Flush the pending works. Should be used by the core kernel code.
 86  * Called before the task returns to the user-mode or stops, or when
 87  * it exits. In the latter case task_work_add() can no longer add the
 88  * new work after task_work_run() returns.
 89  */
 90 void task_work_run(void)
 91 {
 92         struct task_struct *task = current;
 93         struct callback_head *work, *head, *next;
 94 
 95         for (;;) {
 96                 /*
 97                  * work->func() can do task_work_add(), do not set
 98                  * work_exited unless the list is empty.
 99                  */
100                 raw_spin_lock_irq(&task->pi_lock);
101                 do {
102                         work = READ_ONCE(task->task_works);
103                         head = !work && (task->flags & PF_EXITING) ?
104                                 &work_exited : NULL;
105                 } while (cmpxchg(&task->task_works, work, head) != work);
106                 raw_spin_unlock_irq(&task->pi_lock);
107 
108                 if (!work)
109                         break;
110 
111                 do {
112                         next = work->next;
113                         work->func(work);
114                         work = next;
115                         cond_resched();
116                 } while (work);
117         }
118 }
119 

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