smb: smbdirect: introduce smbdirect_socket.send_io.bcredits.*

It turns out that our code will corrupt the stream of
reassabled data transfer messages when we trigger an
immendiate (empty) send.

In order to fix this we'll have a single 'batch' credit per
connection. And code getting that credit is free to use
as much messages until remaining_length reaches 0, then
the batch credit it given back and the next logical send can
happen.

Cc: <stable@vger.kernel.org> # 6.18.x
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: metze-samba

fs/smb/common/smbdirect/smbdirect_socket.h

@@ -162,6 +162,17 @@ struct smbdirect_socket {
 			mempool_t		*pool;
 		} mem;
 
+		/*
+		 * This is a coordination for smbdirect_send_batch.
+		 *
+		 * There's only one possible credit, which means
+		 * only one instance is running at a time.
+		 */
+		struct {
+			atomic_t count;
+			wait_queue_head_t wait_queue;
+		} bcredits;
+
 		/*
 		 * The local credit state for ib_post_send()
 		 */
@@ -371,6 +382,9 @@ static __always_inline void smbdirect_socket_init(struct smbdirect_socket *sc)
 	INIT_DELAYED_WORK(&sc->idle.timer_work, __smbdirect_socket_disabled_work);
 	disable_delayed_work_sync(&sc->idle.timer_work);
 
+	atomic_set(&sc->send_io.bcredits.count, 0);
+	init_waitqueue_head(&sc->send_io.bcredits.wait_queue);
+
 	atomic_set(&sc->send_io.lcredits.count, 0);
 	init_waitqueue_head(&sc->send_io.lcredits.wait_queue);
 
@@ -485,6 +499,8 @@ struct smbdirect_send_batch {
 	 */
 	bool need_invalidate_rkey;
 	u32 remote_key;
+
+	int credit;
 };
 
 struct smbdirect_recv_io {