io_uring: split tw fallback into a function

When the target process is dying and so task_work_add() is not allowed
we push all task_work item to the fallback workqueue. Move the part
responsible for moving tw items out of __io_req_task_work_add() into
a separate function. Makes it a bit cleaner and gives the compiler a bit
of extra info.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e503dab9d7af95470ca6b214c6de17715ae4e748.1668162751.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -1105,6 +1105,20 @@ void tctx_task_work(struct callback_head *cb)
 	trace_io_uring_task_work_run(tctx, count, loops);
 }
 
+static __cold void io_fallback_tw(struct io_uring_task *tctx)
+{
+	struct llist_node *node = llist_del_all(&tctx->task_list);
+	struct io_kiocb *req;
+
+	while (node) {
+		req = container_of(node, struct io_kiocb, io_task_work.node);
+		node = node->next;
+		if (llist_add(&req->io_task_work.node,
+			      &req->ctx->fallback_llist))
+			schedule_delayed_work(&req->ctx->fallback_work, 1);
+	}
+}
+
 static void io_req_local_work_add(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -1131,7 +1145,6 @@ void __io_req_task_work_add(struct io_kiocb *req, bool allow_local)
 {
 	struct io_uring_task *tctx = req->task->io_uring;
 	struct io_ring_ctx *ctx = req->ctx;
-	struct llist_node *node;
 
 	if (allow_local && ctx->flags & IORING_SETUP_DEFER_TASKRUN) {
 		io_req_local_work_add(req);
@@ -1148,15 +1161,7 @@ void __io_req_task_work_add(struct io_kiocb *req, bool allow_local)
 	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.node,
-			      &req->ctx->fallback_llist))
-			schedule_delayed_work(&req->ctx->fallback_work, 1);
-	}
+	io_fallback_tw(tctx);
 }
 
 static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)