1 files changed, 184 insertions, 0 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c
new file mode 100644
index 000000000..065e1ef8f
--- /dev/null
+++ b/kernel/task_work.c
@@ -0,0 +1,184 @@
+// 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);
+	}
+}