firewire: fw-sbp2: fix races

1: There is a small race between queue_delayed_work() and its
   corresponding kref_get().  Do the kref_get first, and _put it again
   if the queue_delayed_work() failed, so there is no chance of the
   kref going to zero while the work is scheduled.
2: An SBP2_LOGOUT_REQUEST could be sent out with a login_id full of
   garbage.  Initialize it to an invalid value so we can tell if we
   ever got a valid login_id.
3: The node ID and generation may have changed but the new values may
   not yet have been recorded in lu and tgt when the final logout is
   attempted.  Use the latest values from the device in
   sbp2_release_target().
Signed-off-by: Jay Fenlason <fenlason@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/fw-sbp2.c

@@ -173,6 +173,9 @@ struct sbp2_target {
 	int blocked;	/* ditto */
 };
 
+/* Impossible login_id, to detect logout attempt before successful login */
+#define INVALID_LOGIN_ID 0x10000
+
 /*
  * Per section 7.4.8 of the SBP-2 spec, a mgt_ORB_timeout value can be
  * provided in the config rom. Most devices do provide a value, which
@@ -788,9 +791,20 @@ static void sbp2_release_target(struct kref *kref)
 			scsi_remove_device(sdev);
 			scsi_device_put(sdev);
 		}
-		sbp2_send_management_orb(lu, tgt->node_id, lu->generation,
-				SBP2_LOGOUT_REQUEST, lu->login_id, NULL);
-
+		if (lu->login_id != INVALID_LOGIN_ID) {
+			int generation, node_id;
+			/*
+			 * tgt->node_id may be obsolete here if we failed
+			 * during initial login or after a bus reset where
+			 * the topology changed.
+			 */
+			generation = device->generation;
+			smp_rmb(); /* node_id vs. generation */
+			node_id    = device->node_id;
+			sbp2_send_management_orb(lu, node_id, generation,
+						 SBP2_LOGOUT_REQUEST,
+						 lu->login_id, NULL);
+		}
 		fw_core_remove_address_handler(&lu->address_handler);
 		list_del(&lu->link);
 		kfree(lu);
@@ -805,19 +819,20 @@ static void sbp2_release_target(struct kref *kref)
 
 static struct workqueue_struct *sbp2_wq;
 
+static void sbp2_target_put(struct sbp2_target *tgt)
+{
+	kref_put(&tgt->kref, sbp2_release_target);
+}
+
 /*
  * Always get the target's kref when scheduling work on one its units.
  * Each workqueue job is responsible to call sbp2_target_put() upon return.
  */
 static void sbp2_queue_work(struct sbp2_logical_unit *lu, unsigned long delay)
 {
-	if (queue_delayed_work(sbp2_wq, &lu->work, delay))
-		kref_get(&lu->tgt->kref);
-}
-
-static void sbp2_target_put(struct sbp2_target *tgt)
-{
-	kref_put(&tgt->kref, sbp2_release_target);
+	kref_get(&lu->tgt->kref);
+	if (!queue_delayed_work(sbp2_wq, &lu->work, delay))
+		sbp2_target_put(lu->tgt);
 }
 
 /*
@@ -978,6 +993,7 @@ static int sbp2_add_logical_unit(struct sbp2_target *tgt, int lun_entry)
 
 	lu->tgt      = tgt;
 	lu->lun      = lun_entry & 0xffff;
+	lu->login_id = INVALID_LOGIN_ID;
 	lu->retries  = 0;
 	lu->has_sdev = false;
 	lu->blocked  = false;