// SPDX-License-Identifier: GPL-2.0
#include <linux/irq_work.h>
#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 */

#ifdef CONFIG_IRQ_WORK
static void task_work_set_notify_irq(struct irq_work *entry)
{
        /*
         * no-op IPI
         *
         * TWA_NMI_CURRENT will already have set the TIF flag, all
         * this interrupt does it tickle the return-to-user path.
         */
}
static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
        IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
#endif

/**
 * 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, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
 *
 * @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.
 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
 * current @task and if the current context is NMI.
 *
 * 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;

        if (notify == TWA_NMI_CURRENT) {
                if (WARN_ON_ONCE(task != current))
                        return -EINVAL;
                if (!IS_ENABLED(CONFIG_IRQ_WORK))
                        return -EINVAL;
        } else {
                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;
#ifdef CONFIG_IRQ_WORK
        case TWA_NMI_CURRENT:
                set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
                irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
                break;
#endif
        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
 * @data: data to be passed in to match function
 *
 * 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_func - cancel a pending work matching a function added by task_work_add()
 * @task: the task which should execute the func's work
 * @func: identifies the func to match with a 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_func(struct task_struct *task, task_work_func_t func)
{
        return task_work_cancel_match(task, task_work_func_match, func);
}

static bool task_work_match(struct callback_head *cb, void *data)
{
        return cb == data;
}

/**
 * task_work_cancel - cancel a pending work added by task_work_add()
 * @task: the task which should execute the work
 * @cb: the callback to remove if queued
 *
 * Remove a callback from a task's queue if queued.
 *
 * RETURNS:
 * True if the callback was queued and got cancelled, false otherwise.
 */
bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
{
        struct callback_head *ret;

        ret = task_work_cancel_match(task, task_work_match, cb);

        return ret == cb;
}

/**
 * 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_match(). 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);
        }
}