io_uring: fuse fallback_node and normal tw node

Now as both normal and fallback paths use llist, just keep one node head
in struct io_task_work and kill off ->fallback_node.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d04ebde409f7b162fe247b361b4486b193293e46.1656153285.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -427,10 +427,7 @@ enum {
 typedef void (*io_req_tw_func_t)(struct io_kiocb *req, bool *locked);
 
 struct io_task_work {
-	union {
-		struct llist_node	node;
-		struct llist_node	fallback_node;
-	};
+	struct llist_node		node;
 	io_req_tw_func_t		func;
 };
 

io_uring/io_uring.c

@@ -233,7 +233,7 @@ static __cold void io_fallback_req_func(struct work_struct *work)
 	bool locked = false;
 
 	percpu_ref_get(&ctx->refs);
-	llist_for_each_entry_safe(req, tmp, node, io_task_work.fallback_node)
+	llist_for_each_entry_safe(req, tmp, node, io_task_work.node)
 		req->io_task_work.func(req, &locked);
 
 	if (locked) {
@@ -1091,13 +1091,12 @@ void io_req_task_work_add(struct io_kiocb *req)
 	if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
 		return;
 
-
 	node = llist_del_all(&tctx->task_list);
 
 	while (node) {
 		req = container_of(node, struct io_kiocb, io_task_work.node);
 		node = node->next;
-		if (llist_add(&req->io_task_work.fallback_node,
+		if (llist_add(&req->io_task_work.node,
 			      &req->ctx->fallback_llist))
 			schedule_delayed_work(&req->ctx->fallback_work, 1);
 	}