linux-kernel - [PATCH 3.16 217/328] batman-adv: Place kref_get for softif

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Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Sven Eckelmann" <sven@...fation.org>,
        "Simon Wunderlich" <sw@...onwunderlich.de>,
        "Marek Lindner" <mareklindner@...mailbox.ch>
Subject: [PATCH 3.16 217/328] batman-adv: Place kref_get for softif_vlan
 near use

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sven Eckelmann <sven@...fation.org>

commit df28ca6bb3282a4c8dc5b65f60b0136fc190ee52 upstream.

It is hard to understand why the refcnt is increased when it isn't done
near the actual place the new reference is used. So using kref_get right
before the place which requires the reference and in the same function
helps to avoid accidental problems caused by incorrect reference counting.

Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
[bwh: Backported to 3.16:
 - s/kref_get/atomic_inc/
 - s/_put/_free_ref/]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/batman-adv/soft-interface.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -529,6 +529,7 @@ int batadv_softif_create_vlan(struct bat
 	}
 
 	spin_lock_bh(&bat_priv->softif_vlan_list_lock);
+	atomic_inc(&vlan->refcount);
 	hlist_add_head_rcu(&vlan->list, &bat_priv->softif_vlan_list);
 	spin_unlock_bh(&bat_priv->softif_vlan_list_lock);
 
@@ -539,6 +540,9 @@ int batadv_softif_create_vlan(struct bat
 			    bat_priv->soft_iface->dev_addr, vid,
 			    BATADV_NULL_IFINDEX, BATADV_NO_MARK);
 
+	/* don't return reference to new softif_vlan */
+	batadv_softif_vlan_free_ref(vlan);
+
 	return 0;
 }