smb: smbdirect: introduce smbdirect_socket.recv_io.credits.available

The logic off managing recv credits by counting posted recv_io and
granted credits is racy.

That's because the peer might already consumed a credit,
but between receiving the incoming recv at the hardware
and processing the completion in the 'recv_done' functions
we likely have a window where we grant credits, which
don't really exist.

So we better have a decicated counter for the
available credits, which will be incremented
when we posted new recv buffers and drained when
we grant the credits to the peer.

Fixes: 5fb9b45 ("smb: client: count the number of posted recv_io messages in order to calculated credits")
Fixes: 89b021a ("smb: server: manage recv credits by counting posted recv_io and granted credits")
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

@@ -239,6 +239,7 @@ struct smbdirect_socket {
 		 */
 		struct {
 			u16 target;
+			atomic_t available;
 			atomic_t count;
 		} credits;
 
@@ -387,6 +388,7 @@ static __always_inline void smbdirect_socket_init(struct smbdirect_socket *sc)
 	INIT_WORK(&sc->recv_io.posted.refill_work, __smbdirect_socket_disabled_work);
 	disable_work_sync(&sc->recv_io.posted.refill_work);
 
+	atomic_set(&sc->recv_io.credits.available, 0);
 	atomic_set(&sc->recv_io.credits.count, 0);
 
 	INIT_LIST_HEAD(&sc->recv_io.reassembly.list);