scsi: core: Fix refcount leak for tagset_refcnt

This leak will cause a hang when tearing down the SCSI host. For example,
iscsid hangs with the following call trace:

[130120.652718] scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured

PID: 2528     TASK: ffff9d0408974e00  CPU: 3    COMMAND: "iscsid"
 #0 [ffffb5b9c134b9e0] __schedule at ffffffff860657d4
 #1 [ffffb5b9c134ba28] schedule at ffffffff86065c6f
 #2 [ffffb5b9c134ba40] schedule_timeout at ffffffff86069fb0
 #3 [ffffb5b9c134bab0] __wait_for_common at ffffffff8606674f
 #4 [ffffb5b9c134bb10] scsi_remove_host at ffffffff85bfe84b
 #5 [ffffb5b9c134bb30] iscsi_sw_tcp_session_destroy at ffffffffc03031c4 [iscsi_tcp]
 #6 [ffffb5b9c134bb48] iscsi_if_recv_msg at ffffffffc0292692 [scsi_transport_iscsi]
 #7 [ffffb5b9c134bb98] iscsi_if_rx at ffffffffc02929c2 [scsi_transport_iscsi]
 #8 [ffffb5b9c134bbf0] netlink_unicast at ffffffff85e551d6
 #9 [ffffb5b9c134bc38] netlink_sendmsg at ffffffff85e554ef

Fixes: 8fe4ce5 ("scsi: core: Fix a use-after-free")
Cc: [email protected]
Signed-off-by: Junxiao Bi <[email protected]>
Reviewed-by: Mike Christie <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>

Author: biger410

drivers/scsi/scsi_scan.c

@@ -361,6 +361,7 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 	 * since we use this queue depth most of times.
 	 */
 	if (scsi_realloc_sdev_budget_map(sdev, depth)) {
+		kref_put(&sdev->host->tagset_refcnt, scsi_mq_free_tags);
 		put_device(&starget->dev);
 		kfree(sdev);
 		goto out;