io_uring/notif: disable LAZY_WAKE for linked notifs

Notifications may now be linked and thus a single tw can post multiple
CQEs, it's not safe to use LAZY_WAKE with them. Disable LAZY_WAKE for
now, if that'd prove to be a problem we can count them and pass the
expected number of CQEs into __io_req_task_work_add().

Fixes: 6fe4220 ("io_uring/notif: implement notification stacking")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0a5accdb7d2d0d27ebec14f8106e14e0192fae17.1714488419.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/notif.c

@@ -38,6 +38,7 @@ void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
 {
 	struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
 	struct io_kiocb *notif = cmd_to_io_kiocb(nd);
+	unsigned tw_flags;
 
 	if (nd->zc_report) {
 		if (success && !nd->zc_used && skb)
@@ -53,8 +54,10 @@ void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
 		io_tx_ubuf_complete(skb, &nd->head->uarg, success);
 		return;
 	}
+
+	tw_flags = nd->next ? 0 : IOU_F_TWQ_LAZY_WAKE;
 	notif->io_task_work.func = io_notif_tw_complete;
-	__io_req_task_work_add(notif, IOU_F_TWQ_LAZY_WAKE);
+	__io_req_task_work_add(notif, tw_flags);
 }
 
 static int io_link_skb(struct sk_buff *skb, struct ubuf_info *uarg)