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
  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                 do {
 101                         head = NULL;
 102                         work = READ_ONCE(task->task_works);
 103                         if (!work) {
 104                                 if (task->flags & PF_EXITING)
 105                                         head = &work_exited;
 106                                 else
 107                                         break;
 108                         }
 109                 } while (cmpxchg(&task->task_works, work, head) != work);
 110
 111                 if (!work)
 112                         break;
 113                 /*
 114                  * Synchronize with task_work_cancel(). It can not remove
 115                  * the first entry == work, cmpxchg(task_works) must fail.
 116                  * But it can remove another entry from the ->next list.
 117                  */
 118                 raw_spin_lock_irq(&task->pi_lock);
 119                 raw_spin_unlock_irq(&task->pi_lock);
 120
 121                 do {
 122                         next = work->next;
 123                         work->func(work);
 124                         work = next;
 125                         cond_resched();
 126                 } while (work);
 127         }
 128 }