[PATCH] task_work: return -EBUSY when adding same work

[yaozhenguo <yaozhenguo1@gmail.com>]

when same work is added to task->task_works list one by one,
the list becomes endless loop. So return -EBUSY when this
situation happen.

Signed-off-by: yaozhenguo <yaozhenguo1@gmail.com>
---
 kernel/task_work.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 1698fbe..5061ebf 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -27,7 +27,7 @@
  * list is LIFO.
  *
  * RETURNS:
- * 0 if succeeds or -ESRCH.
+ * 0 if succeeds or -ESRCH, -EBUSY.
  */
 int task_work_add(struct task_struct *task, struct callback_head *work,
 		  enum task_work_notify_mode notify)
@@ -41,6 +41,8 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 		head = READ_ONCE(task->task_works);
 		if (unlikely(head == &work_exited))
 			return -ESRCH;
+		if (unlikely(head == work))
+			return -EBUSY;
 		work->next = head;
 	} while (cmpxchg(&task->task_works, head, work) != head);
 
-- 
1.8.3.1