smb: server: make sure we call ib_dma_unmap_single() only if we called ib_dma_map_single already

In case of failures either ib_dma_map_single() might not be called yet
or ib_dma_unmap_single() was already called.

We should make sure put_recvmsg() only calls ib_dma_unmap_single() if needed.

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
Fixes: 0626e66 ("cifsd: add server handler for central processing and tranport layers")
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

@@ -265,8 +265,13 @@ smb_direct_recvmsg *get_free_recvmsg(struct smb_direct_transport *t)
 static void put_recvmsg(struct smb_direct_transport *t,
 			struct smb_direct_recvmsg *recvmsg)
 {
-	ib_dma_unmap_single(t->cm_id->device, recvmsg->sge.addr,
-			    recvmsg->sge.length, DMA_FROM_DEVICE);
+	if (likely(recvmsg->sge.length != 0)) {
+		ib_dma_unmap_single(t->cm_id->device,
+				    recvmsg->sge.addr,
+				    recvmsg->sge.length,
+				    DMA_FROM_DEVICE);
+		recvmsg->sge.length = 0;
+	}
 
 	spin_lock(&t->recvmsg_queue_lock);
 	list_add(&recvmsg->list, &t->recvmsg_queue);
@@ -638,6 +643,7 @@ static int smb_direct_post_recv(struct smb_direct_transport *t,
 		ib_dma_unmap_single(t->cm_id->device,
 				    recvmsg->sge.addr, recvmsg->sge.length,
 				    DMA_FROM_DEVICE);
+		recvmsg->sge.length = 0;
 		smb_direct_disconnect_rdma_connection(t);
 		return ret;
 	}
@@ -1819,6 +1825,7 @@ static int smb_direct_create_pools(struct smb_direct_transport *t)
 		if (!recvmsg)
 			goto err;
 		recvmsg->transport = t;
+		recvmsg->sge.length = 0;
 		list_add(&recvmsg->list, &t->recvmsg_queue);
 	}
 	t->count_avail_recvmsg = t->recv_credit_max;