Merge tag 'v4.9.166' into 4.9-2.3.x-imx

This is the 4.9.166 stable release

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a4112dfcd0fb..be06c45cbe4f 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -195,15 +195,22 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem,
 		woken++;
 		tsk = waiter->task;
 
-		wake_q_add(wake_q, tsk);
+		get_task_struct(tsk);
 		list_del(&waiter->list);
 		/*
-		 * Ensure that the last operation is setting the reader
+		 * Ensure calling get_task_struct() before setting the reader
 		 * waiter to nil such that rwsem_down_read_failed() cannot
 		 * race with do_exit() by always holding a reference count
 		 * to the task to wakeup.
 		 */
 		smp_store_release(&waiter->task, NULL);
+		/*
+		 * Ensure issuing the wakeup (either by us or someone else)
+		 * after setting the reader waiter to nil.
+		 */
+		wake_q_add(wake_q, tsk);
+		/* wake_q_add() already take the task ref */
+		put_task_struct(tsk);
 	}
 
 	adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;