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- // SPDX-License-Identifier: GPL-2.0
- #include <linux/spinlock.h>
- #include <linux/task_work.h>
- #include <linux/resume_user_mode.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, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI.
- *
- * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
- * task and run the task_work, regardless of whether the task is currently
- * running in the kernel or userspace.
- * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a
- * reschedule IPI to force the targeted task to reschedule and run task_work.
- * This can be advantageous if there's no strict requirement that the
- * task_work be run as soon as possible, just whenever the task enters the
- * kernel anyway.
- * @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;
- /* record the work call stack in order to print it in KASAN reports */
- kasan_record_aux_stack(work);
- head = READ_ONCE(task->task_works);
- do {
- if (unlikely(head == &work_exited))
- return -ESRCH;
- work->next = head;
- } while (!try_cmpxchg(&task->task_works, &head, work));
- switch (notify) {
- case TWA_NONE:
- break;
- case TWA_RESUME:
- set_notify_resume(task);
- break;
- case TWA_SIGNAL:
- set_notify_signal(task);
- break;
- case TWA_SIGNAL_NO_IPI:
- __set_notify_signal(task);
- break;
- default:
- WARN_ON_ONCE(1);
- break;
- }
- return 0;
- }
- /**
- * task_work_cancel_match - cancel a pending work added by task_work_add()
- * @task: the task which should execute the work
- * @match: match function to call
- *
- * RETURNS:
- * The found work or NULL if not found.
- */
- struct callback_head *
- task_work_cancel_match(struct task_struct *task,
- bool (*match)(struct callback_head *, void *data),
- void *data)
- {
- struct callback_head **pprev = &task->task_works;
- struct callback_head *work;
- unsigned long flags;
- if (likely(!task_work_pending(task)))
- 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);
- work = READ_ONCE(*pprev);
- while (work) {
- if (!match(work, data)) {
- pprev = &work->next;
- work = READ_ONCE(*pprev);
- } else if (try_cmpxchg(pprev, &work, work->next))
- break;
- }
- raw_spin_unlock_irqrestore(&task->pi_lock, flags);
- return work;
- }
- static bool task_work_func_match(struct callback_head *cb, void *data)
- {
- return cb->func == data;
- }
- /**
- * 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)
- {
- return task_work_cancel_match(task, task_work_func_match, func);
- }
- /**
- * 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.
- */
- work = READ_ONCE(task->task_works);
- do {
- head = NULL;
- if (!work) {
- if (task->flags & PF_EXITING)
- head = &work_exited;
- else
- break;
- }
- } while (!try_cmpxchg(&task->task_works, &work, head));
- 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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