nvmet-tcp: add an helper to free the cmd buffers

Makes the code easier to read and to debug.

Sets the freed pointers to NULL, it will be useful
when destroying the queues to understand if the commands'
buffers have been released already or not.
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: John Meneghini <jmeneghi@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/tcp.c

@@ -166,6 +166,8 @@ static struct workqueue_struct *nvmet_tcp_wq;
 static const struct nvmet_fabrics_ops nvmet_tcp_ops;
 static void nvmet_tcp_free_cmd(struct nvmet_tcp_cmd *c);
 static void nvmet_tcp_finish_cmd(struct nvmet_tcp_cmd *cmd);
+static void nvmet_tcp_free_cmd_buffers(struct nvmet_tcp_cmd *cmd);
+static void nvmet_tcp_unmap_pdu_iovec(struct nvmet_tcp_cmd *cmd);
 
 static inline u16 nvmet_tcp_cmd_tag(struct nvmet_tcp_queue *queue,
 		struct nvmet_tcp_cmd *cmd)
@@ -297,6 +299,16 @@ static int nvmet_tcp_check_ddgst(struct nvmet_tcp_queue *queue, void *pdu)
 	return 0;
 }
 
+static void nvmet_tcp_free_cmd_buffers(struct nvmet_tcp_cmd *cmd)
+{
+	WARN_ON(unlikely(cmd->nr_mapped > 0));
+
+	kfree(cmd->iov);
+	sgl_free(cmd->req.sg);
+	cmd->iov = NULL;
+	cmd->req.sg = NULL;
+}
+
 static void nvmet_tcp_unmap_pdu_iovec(struct nvmet_tcp_cmd *cmd)
 {
 	struct scatterlist *sg;
@@ -306,6 +318,8 @@ static void nvmet_tcp_unmap_pdu_iovec(struct nvmet_tcp_cmd *cmd)
 
 	for (i = 0; i < cmd->nr_mapped; i++)
 		kunmap(sg_page(&sg[i]));
+
+	cmd->nr_mapped = 0;
 }
 
 static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd)
@@ -387,7 +401,7 @@ static int nvmet_tcp_map_data(struct nvmet_tcp_cmd *cmd)
 
 	return 0;
 err:
-	sgl_free(cmd->req.sg);
+	nvmet_tcp_free_cmd_buffers(cmd);
 	return NVME_SC_INTERNAL;
 }
 
@@ -632,10 +646,8 @@ static int nvmet_try_send_data(struct nvmet_tcp_cmd *cmd, bool last_in_batch)
 		}
 	}
 
-	if (queue->nvme_sq.sqhd_disabled) {
-		kfree(cmd->iov);
-		sgl_free(cmd->req.sg);
-	}
+	if (queue->nvme_sq.sqhd_disabled)
+		nvmet_tcp_free_cmd_buffers(cmd);
 
 	return 1;
 
@@ -664,8 +676,7 @@ static int nvmet_try_send_response(struct nvmet_tcp_cmd *cmd,
 	if (left)
 		return -EAGAIN;
 
-	kfree(cmd->iov);
-	sgl_free(cmd->req.sg);
+	nvmet_tcp_free_cmd_buffers(cmd);
 	cmd->queue->snd_cmd = NULL;
 	nvmet_tcp_put_cmd(cmd);
 	return 1;
@@ -1406,8 +1417,7 @@ static void nvmet_tcp_finish_cmd(struct nvmet_tcp_cmd *cmd)
 {
 	nvmet_req_uninit(&cmd->req);
 	nvmet_tcp_unmap_pdu_iovec(cmd);
-	kfree(cmd->iov);
-	sgl_free(cmd->req.sg);
+	nvmet_tcp_free_cmd_buffers(cmd);
 }
 
 static void nvmet_tcp_uninit_data_in_cmds(struct nvmet_tcp_queue *queue)