linux/kernel/task_work.c

// 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)
{ … }
static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) = …;
#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)
{ … }

/**
 * 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)
{ … }

static bool task_work_func_match(struct callback_head *cb, void *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)
{ … }

static bool task_work_match(struct callback_head *cb, void *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)
{ … }

/**
 * 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)
{ … }