batman-adv: mcast: shorten multicast tt/tvlv worker spinlock section

It is not necessary to hold the mla_lock spinlock during the whole
multicast tt/tvlv worker callback. Just holding it during the checks and
updates of the bat_priv stored multicast flags and mla_list is enough.

Therefore this patch splits batadv_mcast_mla_tvlv_update() in two:
batadv_mcast_mla_flags_get() at the beginning of the worker to gather
and calculate the new multicast flags, which does not need any locking
as it neither reads from nor writes to bat_priv->mcast.

And batadv_mcast_mla_flags_update() at the end of the worker which
commits the newly calculated flags and lists to bat_priv->mcast and
therefore needs the lock.
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/soft-interface.c

@@ -804,11 +804,6 @@ static int batadv_softif_init_late(struct net_device *dev)
 	atomic_set(&bat_priv->distributed_arp_table, 1);
 #endif
 #ifdef CONFIG_BATMAN_ADV_MCAST
-	bat_priv->mcast.querier_ipv4.exists = false;
-	bat_priv->mcast.querier_ipv4.shadowing = false;
-	bat_priv->mcast.querier_ipv6.exists = false;
-	bat_priv->mcast.querier_ipv6.shadowing = false;
-	bat_priv->mcast.flags = BATADV_NO_FLAGS;
 	atomic_set(&bat_priv->multicast_mode, 1);
 	atomic_set(&bat_priv->multicast_fanout, 16);
 	atomic_set(&bat_priv->mcast.num_want_all_unsnoopables, 0);

net/batman-adv/types.h

@@ -1170,6 +1170,26 @@ struct batadv_mcast_querier_state {
 	unsigned char shadowing:1;
 };
 
+/**
+ * struct batadv_mcast_mla_flags - flags for the querier, bridge and tvlv state
+ */
+struct batadv_mcast_mla_flags {
+	/** @querier_ipv4: the current state of an IGMP querier in the mesh */
+	struct batadv_mcast_querier_state querier_ipv4;
+
+	/** @querier_ipv6: the current state of an MLD querier in the mesh */
+	struct batadv_mcast_querier_state querier_ipv6;
+
+	/** @enabled: whether the multicast tvlv is currently enabled */
+	unsigned char enabled:1;
+
+	/** @bridged: whether the soft interface has a bridge on top */
+	unsigned char bridged:1;
+
+	/** @tvlv_flags: the flags we have last sent in our mcast tvlv */
+	u8 tvlv_flags;
+};
+
 /**
  * struct batadv_priv_mcast - per mesh interface mcast data
  */
@@ -1198,20 +1218,10 @@ struct batadv_priv_mcast {
 	 */
 	struct hlist_head want_all_ipv6_list;
 
-	/** @querier_ipv4: the current state of an IGMP querier in the mesh */
-	struct batadv_mcast_querier_state querier_ipv4;
-
-	/** @querier_ipv6: the current state of an MLD querier in the mesh */
-	struct batadv_mcast_querier_state querier_ipv6;
-
-	/** @flags: the flags we have last sent in our mcast tvlv */
-	u8 flags;
-
-	/** @enabled: whether the multicast tvlv is currently enabled */
-	unsigned char enabled:1;
-
-	/** @bridged: whether the soft interface has a bridge on top */
-	unsigned char bridged:1;
+	/**
+	 * @mla_flags: flags for the querier, bridge and tvlv state
+	 */
+	struct batadv_mcast_mla_flags mla_flags;
 
 	/**
 	 * @mla_lock: a lock protecting mla_list and mla_flags