kernel/task_work.c

   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  * RETURNS:
  22  * 0 if succeeds or -ESRCH.
  23  */
  24 int
  25 task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
  26 {
  27         struct callback_head *head;
  28
  29         do {
  30                 head = ACCESS_ONCE(task->task_works);
  31                 if (unlikely(head == &work_exited))
  32                         return -ESRCH;
  33                 work->next = head;
  34         } while (cmpxchg(&task->task_works, head, work) != head);
  35
  36         if (notify)
  37                 set_notify_resume(task);
  38         return 0;
  39 }
  40
  41 /**
  42  * task_work_cancel - cancel a pending work added by task_work_add()
  43  * @task: the task which should execute the work
  44  * @func: identifies the work to remove
  45  *
  46  * Find the last queued pending work with ->func == @func and remove
  47  * it from queue.
  48  *
  49  * RETURNS:
  50  * The found work or NULL if not found.
  51  */
  52 struct callback_head *
  53 task_work_cancel(struct task_struct *task, task_work_func_t func)
  54 {
  55         struct callback_head **pprev = &task->task_works;
  56         struct callback_head *work;
  57         unsigned long flags;
  58         /*
  59          * If cmpxchg() fails we continue without updating pprev.
  60          * Either we raced with task_work_add() which added the
  61          * new entry before this work, we will find it again. Or
  62          * we raced with task_work_run(), *pprev == NULL/exited.
  63          */
  64         raw_spin_lock_irqsave(&task->pi_lock, flags);
  65         while ((work = ACCESS_ONCE(*pprev))) {
  66                 smp_read_barrier_depends();
  67                 if (work->func != func)
  68                         pprev = &work->next;
  69                 else if (cmpxchg(pprev, work, work->next) == work)
  70                         break;
  71         }
  72         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
  73
  74         return work;
  75 }
  76
  77 /**
  78  * task_work_run - execute the works added by task_work_add()
  79  *
  80  * Flush the pending works. Should be used by the core kernel code.
  81  * Called before the task returns to the user-mode or stops, or when
  82  * it exits. In the latter case task_work_add() can no longer add the
  83  * new work after task_work_run() returns.
  84  */
  85 void task_work_run(void)
  86 {
  87         struct task_struct *task = current;
  88         struct callback_head *work, *head, *next;
  89
  90         for (;;) {
  91                 /*
  92                  * work->func() can do task_work_add(), do not set
  93                  * work_exited unless the list is empty.
  94                  */
  95                 do {
  96                         work = ACCESS_ONCE(task->task_works);
  97                         head = !work && (task->flags & PF_EXITING) ?
  98                                 &work_exited : NULL;
  99                 } while (cmpxchg(&task->task_works, work, head) != work);
 100
 101                 if (!work)
 102                         break;
 103                 /*
 104                  * Synchronize with task_work_cancel(). It can't remove
 105                  * the first entry == work, cmpxchg(task_works) should
 106                  * fail, but it can play with *work and other entries.
 107                  */
 108                 raw_spin_unlock_wait(&task->pi_lock);
 109                 smp_mb();
 110
 111                 /* Reverse the list to run the works in fifo order */
 112                 head = NULL;
 113                 do {
 114                         next = work->next;
 115                         work->next = head;
 116                         head = work;
 117                         work = next;
 118                 } while (work);
 119
 120                 work = head;
 121                 do {
 122                         next = work->next;
 123                         work->func(work);
 124                         work = next;
 125                         cond_resched();
 126                 } while (work);
 127         }
 128 }