---

yaml
---
r: 323602
b: refs/heads/master
c: 9da33de
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: ac3d0da8f3290b3d394cdb7f50604424a7cd6092
+refs/heads/master: 9da33de62431c7839f98156720862262272a8380

trunk/include/linux/task_work.h

@@ -18,8 +18,7 @@ void task_work_run(void);
 
 static inline void exit_task_work(struct task_struct *task)
 {
-	if (unlikely(task->task_works))
-		task_work_run();
+	task_work_run();
 }
 
 #endif	/* _LINUX_TASK_WORK_H */

trunk/kernel/task_work.c

@@ -2,16 +2,17 @@
 #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;
-	/*
-	 * Not inserting the new work if the task has already passed
-	 * exit_task_work() is the responisbility of callers.
-	 */
+
 	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);
 
@@ -30,7 +31,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
 	 * 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.
+	 * we raced with task_work_run(), *pprev == NULL/exited.
 	 */
 	raw_spin_lock_irqsave(&task->pi_lock, flags);
 	while ((work = ACCESS_ONCE(*pprev))) {
@@ -51,7 +52,16 @@ void task_work_run(void)
 	struct callback_head *work, *head, *next;
 
 	for (;;) {
-		work = xchg(&task->task_works, NULL);
+		/*
+		 * 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;
 		/*