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- // SPDX-License-Identifier: GPL-2.0
- #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: how to notify the targeted task
- *
- * Queue @work for task_work_run() below and notify the @task if @notify
- * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL works like signals, in that the
- * it will interrupt the targeted task and run the task_work. @TWA_RESUME
- * work is run only when the task exits the kernel and returns to user mode,
- * or before entering guest mode. Fails if the @task is exiting/exited and thus
- * it can't process this @work. Otherwise @work->func() will be called when the
- * @task goes through one of the aforementioned transitions, or exits.
- *
- * If the targeted task is exiting, then an error is returned and the work item
- * is not queued. It's up to the caller to arrange for an alternative mechanism
- * in that case.
- *
- * Note: there is no ordering guarantee on works queued here. The task_work
- * list is LIFO.
- *
- * RETURNS:
- * 0 if succeeds or -ESRCH.
- */
- int task_work_add(struct task_struct *task, struct callback_head *work,
- enum task_work_notify_mode notify)
- {
- struct callback_head *head;
- unsigned long flags;
- /* record the work call stack in order to print it in KASAN reports */
- kasan_record_aux_stack(work);
- do {
- head = READ_ONCE(task->task_works);
- if (unlikely(head == &work_exited))
- return -ESRCH;
- work->next = head;
- } while (cmpxchg(&task->task_works, head, work) != head);
- switch (notify) {
- case TWA_NONE:
- break;
- case TWA_RESUME:
- set_notify_resume(task);
- break;
- case TWA_SIGNAL:
- /*
- * Only grab the sighand lock if we don't already have some
- * task_work pending. This pairs with the smp_store_mb()
- * in get_signal(), see comment there.
- */
- if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
- lock_task_sighand(task, &flags)) {
- task->jobctl |= JOBCTL_TASK_WORK;
- signal_wake_up(task, 0);
- unlock_task_sighand(task, &flags);
- }
- break;
- default:
- WARN_ON_ONCE(1);
- break;
- }
- 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 (likely(!task->task_works))
- return NULL;
- /*
- * 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 = READ_ONCE(*pprev))) {
- 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 {
- head = NULL;
- work = READ_ONCE(task->task_works);
- if (!work) {
- if (task->flags & PF_EXITING)
- head = &work_exited;
- else
- break;
- }
- } while (cmpxchg(&task->task_works, work, head) != work);
- if (!work)
- break;
- /*
- * Synchronize with task_work_cancel(). It can not remove
- * the first entry == work, cmpxchg(task_works) must fail.
- * But it can remove another entry from the ->next list.
- */
- raw_spin_lock_irq(&task->pi_lock);
- raw_spin_unlock_irq(&task->pi_lock);
- do {
- next = work->next;
- work->func(work);
- work = next;
- cond_resched();
- } while (work);
- }
- }
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