[bug report] scsi: cxgb4i: Add support for iSCSI segmentation offload

[<dan.carpenter@oracle.com>]

Hello Varun Prakash,

The patch e33c2482289b: "scsi: cxgb4i: Add support for iSCSI
segmentation offload" from Jun 29, 2020, leads to the following
static checker warning:

drivers/scsi/cxgbi/libcxgbi.c:1902 cxgbi_conn_alloc_pdu() warn: 'tdata' can't be NULL.
drivers/scsi/cxgbi/libcxgbi.c:2158 cxgbi_conn_init_pdu() warn: 'tdata' can't be NULL.
drivers/scsi/cxgbi/libcxgbi.c:2374 cxgbi_conn_xmit_pdu() warn: 'tdata' can't be NULL.

drivers/scsi/cxgbi/libcxgbi.c
  1885  int cxgbi_conn_alloc_pdu(struct iscsi_task *task, u8 op)
  1886  {
  1887          struct iscsi_conn *conn = task->conn;
  1888          struct iscsi_session *session = task->conn->session;
  1889          struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
  1890          struct cxgbi_conn *cconn = tcp_conn->dd_data;
  1891          struct cxgbi_device *cdev = cconn->chba->cdev;
  1892          struct cxgbi_sock *csk = cconn->cep ? cconn->cep->csk : NULL;
  1893          struct iscsi_tcp_task *tcp_task = task->dd_data;
  1894          struct cxgbi_task_data *tdata = iscsi_task_cxgbi_data(task);
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#define iscsi_task_cxgbi_data(task) \
        ((task)->dd_data + sizeof(struct iscsi_tcp_task))

  1895          struct scsi_cmnd *sc = task->sc;
  1896          u32 headroom = SKB_TX_ISCSI_PDU_HEADER_MAX;
  1897          u32 max_txdata_len = conn->max_xmit_dlength;
  1898          u32 iso_tx_rsvd = 0, local_iso_info = 0;
  1899          u32 last_tdata_offset, last_tdata_count;
  1900          int err = 0;
  1901  
  1902          if (!tcp_task || !tdata) {
                                 ^^^^^^
If ->dd_data is negative sizeof(struct iscsi_tcp_task) then we are
toasted.  That's an error pointer.  These sorts of extra NULL checking
generate a warning because maybe we intended to check a different
variable or IS_ERR(task->dd_data) or something.  The checker can't know.

  1903                  pr_err("task 0x%p, tcp_task 0x%p, tdata 0x%p.\n",
  1904                         task, tcp_task, tdata);
  1905                  return -ENOMEM;
  1906          }

regards,
dan carpenter