linux/kernel/task_work.c

#include <linux/spinlock.h>
#include <linux/task_work.h>
#include <linux/tracehook.h>

int
task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
{
	unsigned long flags;
	int err = -ESRCH;

#ifndef TIF_NOTIFY_RESUME
	if (notify)
		return -ENOTSUPP;
#endif
	/*
	 * We must not insert the new work if the task has already passed
	 * exit_task_work(). We rely on do_exit()->raw_spin_unlock_wait()
	 * and check PF_EXITING under pi_lock.
	 */
	raw_spin_lock_irqsave(&task->pi_lock, flags);
	if (likely(!(task->flags & PF_EXITING))) {
		hlist_add_head(&twork->hlist, &task->task_works);
		err = 0;
	}
	raw_spin_unlock_irqrestore(&task->pi_lock, flags);

	/* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
	if (likely(!err) && notify)
		set_notify_resume(task);
	return err;
}

struct task_work *
task_work_cancel(struct task_struct *task, task_work_func_t func)
{
	unsigned long flags;
	struct task_work *twork;
	struct hlist_node *pos;

	raw_spin_lock_irqsave(&task->pi_lock, flags);
	hlist_for_each_entry(twork, pos, &task->task_works, hlist) {
		if (twork->func == func) {
			hlist_del(&twork->hlist);
			goto found;
		}
	}
	twork = NULL;
 found:
	raw_spin_unlock_irqrestore(&task->pi_lock, flags);

	return twork;
}

void task_work_run(void)
{
	struct task_struct *task = current;
	struct hlist_head task_works;
	struct hlist_node *pos;

	raw_spin_lock_irq(&task->pi_lock);
	hlist_move_list(&task->task_works, &task_works);
	raw_spin_unlock_irq(&task->pi_lock);

	if (unlikely(hlist_empty(&task_works)))
		return;
	/*
	 * We use hlist to save the space in task_struct, but we want fifo.
	 * Find the last entry, the list should be short, then process them
	 * in reverse order.
	 */
	for (pos = task_works.first; pos->next; pos = pos->next)
		;

	for (;;) {
		struct hlist_node **pprev = pos->pprev;
		struct task_work *twork = container_of(pos, struct task_work,
							hlist);
		twork->func(twork);

		if (pprev == &task_works.first)
			break;
		pos = container_of(pprev, struct hlist_node, next);
	}
}