batman-adv: replace non-atomic packet_size_max with (READ|WRITE)_ONCE

The maximum packet size of an meshif is only accessed as plain loads/stores
and does not require full atomic_t semantics. Convert to a native integer
and replace its users with READ_ONCE()/WRITE_ONCE() to avoid load/store
tearing.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

Author: ecsv

net/batman-adv/hard-interface.c

@@ -7,7 +7,6 @@
 #include "hard-interface.h"
 #include "main.h"
 
-#include <linux/atomic.h>
 #include <linux/bug.h>
 #include <linux/byteorder/generic.h>
 #include <linux/compiler.h>
@@ -629,7 +628,7 @@ int batadv_hardif_min_mtu(struct net_device *mesh_iface)
 	 * overhead). For example, this value is used by TT to compute the
 	 * maximum local table size
 	 */
-	atomic_set(&bat_priv->packet_size_max, min_mtu);
+	WRITE_ONCE(bat_priv->packet_size_max, min_mtu);
 
 	/* the real mesh-interface MTU is computed by removing the payload
 	 * overhead from the maximum amount of bytes that was just computed.

net/batman-adv/mesh-interface.c

@@ -779,7 +779,7 @@ static int batadv_meshif_init_late(struct net_device *dev)
 	WRITE_ONCE(bat_priv->log_level, 0);
 #endif
 	WRITE_ONCE(bat_priv->fragmentation, 1);
-	atomic_set(&bat_priv->packet_size_max, BATADV_MAX_MTU);
+	WRITE_ONCE(bat_priv->packet_size_max, BATADV_MAX_MTU);
 	atomic_set(&bat_priv->bcast_queue_left, BATADV_BCAST_QUEUE_LEN);
 	atomic_set(&bat_priv->batman_queue_left, BATADV_BATMAN_QUEUE_LEN);
 

net/batman-adv/translation-table.c

@@ -649,7 +649,7 @@ bool batadv_tt_local_add(struct net_device *mesh_iface, const u8 *addr,
 	/* Ignore the client if we cannot send it in a full table response. */
 	table_size = batadv_tt_local_table_transmit_size(bat_priv);
 	table_size += batadv_tt_len(1);
-	packet_size_max = atomic_read(&bat_priv->packet_size_max);
+	packet_size_max = READ_ONCE(bat_priv->packet_size_max);
 	if (table_size > packet_size_max) {
 		net_ratelimited_function(batadv_info, mesh_iface,
 					 "Local translation table size (%i) exceeds maximum packet size (%i); Ignoring new local tt entry: %pM\n",
@@ -3069,7 +3069,7 @@ static bool batadv_send_other_tt_response(struct batadv_priv *bat_priv,
 
 	/* Don't send the response, if larger than fragmented packet. */
 	tt_len = sizeof(struct batadv_unicast_tvlv_packet) + tvlv_len;
-	if (tt_len > atomic_read(&bat_priv->packet_size_max)) {
+	if (tt_len > READ_ONCE(bat_priv->packet_size_max)) {
 		net_ratelimited_function(batadv_info, bat_priv->mesh_iface,
 					 "Ignoring TT_REQUEST from %pM; Response size exceeds max packet size.\n",
 					 res_dst_orig_node->orig);
@@ -3932,7 +3932,7 @@ bool batadv_tt_add_temporary_global_entry(struct batadv_priv *bat_priv,
 void batadv_tt_local_resize_to_mtu(struct net_device *mesh_iface)
 {
 	struct batadv_priv *bat_priv = netdev_priv(mesh_iface);
-	int packet_size_max = atomic_read(&bat_priv->packet_size_max);
+	int packet_size_max = READ_ONCE(bat_priv->packet_size_max);
 	int table_size, timeout = BATADV_TT_LOCAL_TIMEOUT / 2;
 	bool reduced = false;
 

net/batman-adv/types.h

@@ -1570,7 +1570,7 @@ struct batadv_priv {
 	 *  multiple fragmented skbs or a single frame if fragmentation is
 	 *  disabled
 	 */
-	atomic_t packet_size_max;
+	int packet_size_max;
 
 	/**
 	 * @frag_seqno: incremental counter to identify chains of egress