scsi: target: tcmu: Use priv pointer in se_cmd

We initialize and clean up the se_cmd's priv pointer under cmd_ring_lock to
point to the corresponding tcmu_cmd.

In the patch that implements tmr_notify callback in tcmu we will use the
priv pointer.

Link: https://lore.kernel.org/r/20200726153510.13077-4-bstroesser@ts.fujitsu.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_user.c

@@ -541,6 +541,8 @@ tcmu_get_block_page(struct tcmu_dev *udev, uint32_t dbi)
 
 static inline void tcmu_free_cmd(struct tcmu_cmd *tcmu_cmd)
 {
+	if (tcmu_cmd->se_cmd)
+		tcmu_cmd->se_cmd->priv = NULL;
 	kfree(tcmu_cmd->dbi);
 	kmem_cache_free(tcmu_cmd_cache, tcmu_cmd);
 }
@@ -1109,10 +1111,11 @@ tcmu_queue_cmd(struct se_cmd *se_cmd)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
 	mutex_lock(&udev->cmdr_lock);
+	se_cmd->priv = tcmu_cmd;
 	ret = queue_cmd_ring(tcmu_cmd, &scsi_ret);
-	mutex_unlock(&udev->cmdr_lock);
 	if (ret < 0)
 		tcmu_free_cmd(tcmu_cmd);
+	mutex_unlock(&udev->cmdr_lock);
 	return scsi_ret;
 }
 
@@ -1179,7 +1182,6 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry *
 		target_complete_cmd(cmd->se_cmd, entry->rsp.scsi_status);
 
 out:
-	cmd->se_cmd = NULL;
 	tcmu_cmd_free_data(cmd, cmd->dbi_cnt);
 	tcmu_free_cmd(cmd);
 }
@@ -1285,6 +1287,7 @@ static void tcmu_check_expired_ring_cmd(struct tcmu_cmd *cmd)
 	set_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags);
 	list_del_init(&cmd->queue_entry);
 	se_cmd = cmd->se_cmd;
+	se_cmd->priv = NULL;
 	cmd->se_cmd = NULL;
 
 	pr_debug("Timing out inflight cmd %u on dev %s.\n",