smb: server: let recv_done() queue a refill when the peer is low on credits

In captures I saw that Windows was granting 191 credits in a batch
when its peer posted a lot of messages. We are asking for a
credit target of 255 and 191 is 252*3/4.

So we also use that logic in order to fill the
recv buffers available to the peer.

Fixes: a7eef61 ("smb: server: queue post_recv_credits_work in put_recvmsg() and avoid count_avail_recvmsg")
Cc: <stable@vger.kernel.org> # 6.18.x
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
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/server/transport_rdma.c

@@ -644,6 +644,7 @@ static void recv_done(struct ib_cq *cq, struct ib_wc *wc)
 		struct smbdirect_data_transfer *data_transfer =
 			(struct smbdirect_data_transfer *)recvmsg->packet;
 		u32 remaining_data_length, data_offset, data_length;
+		int current_recv_credits;
 		u16 old_recv_credit_target;
 
 		if (wc->byte_len <
@@ -682,7 +683,7 @@ static void recv_done(struct ib_cq *cq, struct ib_wc *wc)
 		}
 
 		atomic_dec(&sc->recv_io.posted.count);
-		atomic_dec(&sc->recv_io.credits.count);
+		current_recv_credits = atomic_dec_return(&sc->recv_io.credits.count);
 
 		old_recv_credit_target = sc->recv_io.credits.target;
 		sc->recv_io.credits.target =
@@ -702,7 +703,8 @@ static void recv_done(struct ib_cq *cq, struct ib_wc *wc)
 			wake_up(&sc->send_io.credits.wait_queue);
 
 		if (data_length) {
-			if (sc->recv_io.credits.target > old_recv_credit_target)
+			if (current_recv_credits <= (sc->recv_io.credits.target / 4) ||
+			    sc->recv_io.credits.target > old_recv_credit_target)
 				queue_work(sc->workqueue, &sc->recv_io.posted.refill_work);
 
 			enqueue_reassembly(sc, recvmsg, (int)data_length);