scsi: lpfc: Fix list_add() corruption in lpfc_drain_txq()

When parsing the txq list in lpfc_drain_txq(), the driver attempts to pass
the requests to the adapter. If such an attempt fails, a local "fail_msg"
string is set and a log message output.  The job is then added to a
completions list for cancellation.

Processing of any further jobs from the txq list continues, but since
"fail_msg" remains set, jobs are added to the completions list regardless
of whether a wqe was passed to the adapter.  If successfully added to
txcmplq, jobs are added to both lists resulting in list corruption.

Fix by clearing the fail_msg string after adding a job to the completions
list. This stops the subsequent jobs from being added to the completions
list unless they had an appropriate failure.

Link: https://lore.kernel.org/r/20210910233159.115896-2-jsmart2021@gmail.com
Co-developed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_sli.c

@@ -21104,6 +21104,7 @@ lpfc_drain_txq(struct lpfc_hba *phba)
 					fail_msg,
 					piocbq->iotag, piocbq->sli4_xritag);
 			list_add_tail(&piocbq->list, &completions);
+			fail_msg = NULL;
 		}
 		spin_unlock_irqrestore(&pring->ring_lock, iflags);
 	}