1 #include <linux/spinlock.h>
2 #include <linux/task_work.h>
3 #include <linux/tracehook.h>
5 static struct callback_head work_exited
; /* all we need is ->next == NULL */
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
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
18 * This is like the signal handler which runs in kernel mode, but it doesn't
19 * try to wake up the @task.
21 * Note: there is no ordering guarantee on works queued here.
24 * 0 if succeeds or -ESRCH.
27 task_work_add(struct task_struct
*task
, struct callback_head
*work
, bool notify
)
29 struct callback_head
*head
;
32 head
= READ_ONCE(task
->task_works
);
33 if (unlikely(head
== &work_exited
))
36 } while (cmpxchg(&task
->task_works
, head
, work
) != head
);
39 set_notify_resume(task
);
44 * task_work_cancel - cancel a pending work added by task_work_add()
45 * @task: the task which should execute the work
46 * @func: identifies the work to remove
48 * Find the last queued pending work with ->func == @func and remove
52 * The found work or NULL if not found.
54 struct callback_head
*
55 task_work_cancel(struct task_struct
*task
, task_work_func_t func
)
57 struct callback_head
**pprev
= &task
->task_works
;
58 struct callback_head
*work
;
61 if (likely(!task
->task_works
))
64 * If cmpxchg() fails we continue without updating pprev.
65 * Either we raced with task_work_add() which added the
66 * new entry before this work, we will find it again. Or
67 * we raced with task_work_run(), *pprev == NULL/exited.
69 raw_spin_lock_irqsave(&task
->pi_lock
, flags
);
70 while ((work
= lockless_dereference(*pprev
))) {
71 if (work
->func
!= func
)
73 else if (cmpxchg(pprev
, work
, work
->next
) == work
)
76 raw_spin_unlock_irqrestore(&task
->pi_lock
, flags
);
82 * task_work_run - execute the works added by task_work_add()
84 * Flush the pending works. Should be used by the core kernel code.
85 * Called before the task returns to the user-mode or stops, or when
86 * it exits. In the latter case task_work_add() can no longer add the
87 * new work after task_work_run() returns.
89 void task_work_run(void)
91 struct task_struct
*task
= current
;
92 struct callback_head
*work
, *head
, *next
;
96 * work->func() can do task_work_add(), do not set
97 * work_exited unless the list is empty.
100 work
= READ_ONCE(task
->task_works
);
101 head
= !work
&& (task
->flags
& PF_EXITING
) ?
103 } while (cmpxchg(&task
->task_works
, work
, head
) != work
);
108 * Synchronize with task_work_cancel(). It can't remove
109 * the first entry == work, cmpxchg(task_works) should
110 * fail, but it can play with *work and other entries.
112 raw_spin_unlock_wait(&task
->pi_lock
);