1 files changed, 92 insertions, 0 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c
new file mode 100644
index 00000000..65bd3c92
--- /dev/null
+++ b/kernel/task_work.c
@@ -0,0 +1,92 @@
+#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 */
+
+int
+task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
+{
+	struct callback_head *head;
+
+	do {
+		head = ACCESS_ONCE(task->task_works);
+		if (unlikely(head == &work_exited))
+			return -ESRCH;
+		work->next = head;
+	} while (cmpxchg(&task->task_works, head, work) != head);
+
+	if (notify)
+		set_notify_resume(task);
+	return 0;
+}
+
+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 = NULL;
+	unsigned long flags;
+	/*
+	 * 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 = ACCESS_ONCE(*pprev))) {
+		read_barrier_depends();
+		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;
+}
+
+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 {
+			work = ACCESS_ONCE(task->task_works);
+			head = !work && (task->flags & PF_EXITING) ?
+				&work_exited : NULL;
+		} while (cmpxchg(&task->task_works, work, head) != work);
+
+		if (!work)
+			break;
+		/*
+		 * Synchronize with task_work_cancel(). It can't remove
+		 * the first entry == work, cmpxchg(task_works) should
+		 * fail, but it can play with *work and other entries.
+		 */
+		raw_spin_unlock_wait(&task->pi_lock);
+		smp_mb();
+
+		/* Reverse the list to run the works in fifo order */
+		head = NULL;
+		do {
+			next = work->next;
+			work->next = head;
+			head = work;
+			work = next;
+		} while (work);
+
+		work = head;
+		do {
+			next = work->next;
+			work->func(work);
+			work = next;
+			cond_resched();
+		} while (work);
+	}
+}