| #include <linux/spinlock.h> |
| #include <linux/task_work.h> |
| #include <linux/tracehook.h> |
| |
| static struct callback_head work_exited; /* all we need is ->next == NULL */ |
| |
| /** |
| * task_work_add - ask the @task to execute @work->func() |
| * @task: the task which should run the callback |
| * @work: the callback to run |
| * @notify: send the notification if true |
| * |
| * Queue @work for task_work_run() below and notify the @task if @notify. |
| * Fails if the @task is exiting/exited and thus it can't process this @work. |
| * Otherwise @work->func() will be called when the @task returns from kernel |
| * mode or exits. |
| * |
| * This is like the signal handler which runs in kernel mode, but it doesn't |
| * try to wake up the @task. |
| * |
| * Note: there is no ordering guarantee on works queued here. |
| * |
| * RETURNS: |
| * 0 if succeeds or -ESRCH. |
| */ |
| int |
| task_work_add(struct task_struct *task, struct callback_head *work, bool notify) |
| { |
| struct callback_head *head; |
| |
| do { |
| head = ACCESS_ONCE(task->task_works); |
| if (unlikely(head == &work_exited)) |
| return -ESRCH; |
| work->next = head; |
| } while (cmpxchg(&task->task_works, head, work) != head); |
| |
| if (notify) |
| set_notify_resume(task); |
| return 0; |
| } |
| |
| /** |
| * task_work_cancel - cancel a pending work added by task_work_add() |
| * @task: the task which should execute the work |
| * @func: identifies the work to remove |
| * |
| * Find the last queued pending work with ->func == @func and remove |
| * it from queue. |
| * |
| * RETURNS: |
| * The found work or NULL if not found. |
| */ |
| struct callback_head * |
| task_work_cancel(struct task_struct *task, task_work_func_t func) |
| { |
| struct callback_head **pprev = &task->task_works; |
| struct callback_head *work; |
| unsigned long flags; |
| /* |
| * If cmpxchg() fails we continue without updating pprev. |
| * Either we raced with task_work_add() which added the |
| * new entry before this work, we will find it again. Or |
| * we raced with task_work_run(), *pprev == NULL/exited. |
| */ |
| raw_spin_lock_irqsave(&task->pi_lock, flags); |
| while ((work = ACCESS_ONCE(*pprev))) { |
| smp_read_barrier_depends(); |
| if (work->func != func) |
| pprev = &work->next; |
| else if (cmpxchg(pprev, work, work->next) == work) |
| break; |
| } |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| |
| return work; |
| } |
| |
| /** |
| * task_work_run - execute the works added by task_work_add() |
| * |
| * Flush the pending works. Should be used by the core kernel code. |
| * Called before the task returns to the user-mode or stops, or when |
| * it exits. In the latter case task_work_add() can no longer add the |
| * new work after task_work_run() returns. |
| */ |
| void task_work_run(void) |
| { |
| struct task_struct *task = current; |
| struct callback_head *work, *head, *next; |
| |
| for (;;) { |
| /* |
| * work->func() can do task_work_add(), do not set |
| * work_exited unless the list is empty. |
| */ |
| do { |
| work = ACCESS_ONCE(task->task_works); |
| head = !work && (task->flags & PF_EXITING) ? |
| &work_exited : NULL; |
| } while (cmpxchg(&task->task_works, work, head) != work); |
| |
| if (!work) |
| break; |
| /* |
| * Synchronize with task_work_cancel(). It can't remove |
| * the first entry == work, cmpxchg(task_works) should |
| * fail, but it can play with *work and other entries. |
| */ |
| raw_spin_unlock_wait(&task->pi_lock); |
| |
| do { |
| next = work->next; |
| work->func(work); |
| work = next; |
| cond_resched(); |
| } while (work); |
| } |
| } |