io-wq: improve wq_list_add_tail()

Prepare nodes that we're going to add before actually linking them, it's
always safer and costs us nothing.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f7e53f0c84c02ed6748c488ed0789b98f8cc6185.1628471125.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.h

@@ -44,6 +44,7 @@ static inline void wq_list_add_after(struct io_wq_work_node *node,
 static inline void wq_list_add_tail(struct io_wq_work_node *node,
 				    struct io_wq_work_list *list)
 {
+	node->next = NULL;
 	if (!list->first) {
 		list->last = node;
 		WRITE_ONCE(list->first, node);
@@ -51,7 +52,6 @@ static inline void wq_list_add_tail(struct io_wq_work_node *node,
 		list->last->next = node;
 		list->last = node;
 	}
-	node->next = NULL;
 }
 
 static inline void wq_list_cut(struct io_wq_work_list *list,