kernel/task_work.c

   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 EXPORT_SYMBOL(task_work_add);
  44
  45 /**
  46  * task_work_cancel - cancel a pending work added by task_work_add()
  47  * @task: the task which should execute the work
  48  * @func: identifies the work to remove
  49  *
  50  * Find the last queued pending work with ->func == @func and remove
  51  * it from queue.
  52  *
  53  * RETURNS:
  54  * The found work or NULL if not found.
  55  */
  56 struct callback_head *
  57 task_work_cancel(struct task_struct *task, task_work_func_t func)
  58 {
  59         struct callback_head **pprev = &task->task_works;
  60         struct callback_head *work;
  61         unsigned long flags;
  62
  63         if (likely(!task->task_works))
  64                 return NULL;
  65         /*
  66          * If cmpxchg() fails we continue without updating pprev.
  67          * Either we raced with task_work_add() which added the
  68          * new entry before this work, we will find it again. Or
  69          * we raced with task_work_run(), *pprev == NULL/exited.
  70          */
  71         raw_spin_lock_irqsave(&task->pi_lock, flags);
  72         while ((work = READ_ONCE(*pprev))) {
  73                 if (work->func != func)
  74                         pprev = &work->next;
  75                 else if (cmpxchg(pprev, work, work->next) == work)
  76                         break;
  77         }
  78         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
  79
  80         return work;
  81 }
  82
  83 /**
  84  * task_work_run - execute the works added by task_work_add()
  85  *
  86  * Flush the pending works. Should be used by the core kernel code.
  87  * Called before the task returns to the user-mode or stops, or when
  88  * it exits. In the latter case task_work_add() can no longer add the
  89  * new work after task_work_run() returns.
  90  */
  91 void task_work_run(void)
  92 {
  93         struct task_struct *task = current;
  94         struct callback_head *work, *head, *next;
  95
  96         for (;;) {
  97                 /*
  98                  * work->func() can do task_work_add(), do not set
  99                  * work_exited unless the list is empty.
 100                  */
 101                 raw_spin_lock_irq(&task->pi_lock);
 102                 do {
 103                         work = READ_ONCE(task->task_works);
 104                         head = !work && (task->flags & PF_EXITING) ?
 105                                 &work_exited : NULL;
 106                 } while (cmpxchg(&task->task_works, work, head) != work);
 107                 raw_spin_unlock_irq(&task->pi_lock);
 108
 109                 if (!work)
 110                         break;
 111
 112                 do {
 113                         next = work->next;
 114                         work->func(work);
 115                         work = next;
 116                         cond_resched();
 117                 } while (work);
 118         }
 119 }
 120 EXPORT_SYMBOL_GPL(task_work_run);