cifs: smbd: Check send queue size before posting a send

Sometimes the remote peer may return more send credits than the send queue
depth. If all the send credits are used to post senasd, we may overflow the
send queue.

Fix this by checking the send queue size before posting a send.
Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smbdirect.c

@@ -287,6 +287,7 @@ static void send_done(struct ib_cq *cq, struct ib_wc *wc)
 	if (atomic_dec_and_test(&request->info->send_pending))
 		wake_up(&request->info->wait_send_pending);
 
+	wake_up(&request->info->wait_post_send);
 
 	mempool_free(request, request->info->request_mempool);
 }
@@ -939,7 +940,14 @@ static int smbd_post_send(struct smbd_connection *info,
 	send_wr.opcode = IB_WR_SEND;
 	send_wr.send_flags = IB_SEND_SIGNALED;
 
-	atomic_inc(&info->send_pending);
+wait_sq:
+	wait_event(info->wait_post_send,
+		atomic_read(&info->send_pending) < info->send_credit_target);
+	if (unlikely(atomic_inc_return(&info->send_pending) >
+				info->send_credit_target)) {
+		atomic_dec(&info->send_pending);
+		goto wait_sq;
+	}
 
 	rc = ib_post_send(info->id->qp, &send_wr, NULL);
 	if (rc) {
@@ -1733,6 +1741,7 @@ static struct smbd_connection *_smbd_get_connection(
 	init_waitqueue_head(&info->wait_send_pending);
 	atomic_set(&info->send_pending, 0);
 
+	init_waitqueue_head(&info->wait_post_send);
 
 	INIT_WORK(&info->disconnect_work, smbd_disconnect_rdma_work);
 	INIT_WORK(&info->post_send_credits_work, smbd_post_send_credits);

fs/cifs/smbdirect.h

@@ -114,6 +114,7 @@ struct smbd_connection {
 	/* Activity accoutning */
 	atomic_t send_pending;
 	wait_queue_head_t wait_send_pending;
+	wait_queue_head_t wait_post_send;
 
 	/* Receive queue */
 	struct list_head receive_queue;