scsi: target/core: Avoid that a kernel oops is triggered when COMPARE AND WRITE fails

Fixes: aa73237d ("scsi: target/core: Always call transport_complete_callback() upon failure")
Reviewed-by: NDavid Disseldorp <ddiss@suse.de>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_transport.c

@@ -1778,7 +1778,7 @@ EXPORT_SYMBOL(target_submit_tmr);
 void transport_generic_request_failure(struct se_cmd *cmd,
 		sense_reason_t sense_reason)
 {
-	int ret = 0;
+	int ret = 0, post_ret;
 
 	pr_debug("-----[ Storage Engine Exception; sense_reason %d\n",
 		 sense_reason);
@@ -1790,7 +1790,7 @@ void transport_generic_request_failure(struct se_cmd *cmd,
 	transport_complete_task_attr(cmd);
 
 	if (cmd->transport_complete_callback)
-		cmd->transport_complete_callback(cmd, false, NULL);
+		cmd->transport_complete_callback(cmd, false, &post_ret);
 
 	if (transport_check_aborted_status(cmd, 1))
 		return;