[PATCH net-next 11/15] batman-adv: annotate hardif_neigh_node last_seen with READ/WRITE_ONCE

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

The last_seen field for batadv_hardif_neigh_node tracks the jiffies value
of the most recent activity and is used to detect timeouts. These accesses
are not consistently protected by a lock, so READ_ONCE/WRITE_ONCE must be
used to prevent data races caused by compiler optimizations.

To avoid an underflow due to an non-strict order read of jiffies vs
last_seen, use jiffies_delta_to_msecs instead of jiffies_to_msecs to
evaluate the delta.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/bat_iv_ogm.c | 6 ++++--
 net/batman-adv/bat_v.c      | 4 +++-
 net/batman-adv/bat_v_elp.c  | 2 +-
 net/batman-adv/originator.c | 2 +-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index d4b6c09db8c7d..4e15af1e245a5 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -1569,7 +1569,7 @@ batadv_iv_ogm_process_per_outif(const struct sk_buff *skb, int ogm_offset,
 		hardif_neigh = batadv_hardif_neigh_get(if_incoming,
 						       ethhdr->h_source);
 		if (hardif_neigh)
-			hardif_neigh->last_seen = jiffies;
+			WRITE_ONCE(hardif_neigh->last_seen, jiffies);
 	}
 
 	router = batadv_orig_router_get(orig_node, if_outgoing);
@@ -2287,9 +2287,11 @@ batadv_iv_ogm_neigh_dump_neigh(struct sk_buff *msg, u32 portid, u32 seq,
 			       struct batadv_hardif_neigh_node *hardif_neigh)
 {
 	unsigned int last_seen_msecs;
+	unsigned long last_seen;
 	void *hdr;
 
-	last_seen_msecs = jiffies_to_msecs(jiffies - hardif_neigh->last_seen);
+	last_seen = READ_ONCE(hardif_neigh->last_seen);
+	last_seen_msecs = jiffies_delta_to_msecs(jiffies - last_seen);
 
 	hdr = genlmsg_put(msg, portid, seq, &batadv_netlink_family,
 			  NLM_F_MULTI, BATADV_CMD_GET_NEIGHBORS);
diff --git a/net/batman-adv/bat_v.c b/net/batman-adv/bat_v.c
index 2679090c3368b..bd2bf2b58635e 100644
--- a/net/batman-adv/bat_v.c
+++ b/net/batman-adv/bat_v.c
@@ -161,10 +161,12 @@ batadv_v_neigh_dump_neigh(struct sk_buff *msg, u32 portid, u32 seq,
 			  struct batadv_hardif_neigh_node *hardif_neigh)
 {
 	unsigned int last_seen_msecs;
+	unsigned long last_seen;
 	u32 throughput;
 	void *hdr;
 
-	last_seen_msecs = jiffies_to_msecs(jiffies - hardif_neigh->last_seen);
+	last_seen = READ_ONCE(hardif_neigh->last_seen);
+	last_seen_msecs = jiffies_delta_to_msecs(jiffies - last_seen);
 	throughput = ewma_throughput_read(&hardif_neigh->bat_v.throughput);
 	throughput = throughput * 100;
 
diff --git a/net/batman-adv/bat_v_elp.c b/net/batman-adv/bat_v_elp.c
index cf84aed0c947e..144bb30d608a8 100644
--- a/net/batman-adv/bat_v_elp.c
+++ b/net/batman-adv/bat_v_elp.c
@@ -534,7 +534,7 @@ static void batadv_v_elp_neigh_update(struct batadv_priv *bat_priv,
 
 	last_seen = jiffies;
 	WRITE_ONCE(neigh->last_seen, last_seen);
-	hardif_neigh->last_seen = last_seen;
+	WRITE_ONCE(hardif_neigh->last_seen, last_seen);
 	hardif_neigh->bat_v.elp_latest_seqno = ntohl(elp_packet->seqno);
 	hardif_neigh->bat_v.elp_interval = ntohl(elp_packet->elp_interval);
 
diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index 352a88056e334..0f47ac3ecc967 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -587,7 +587,7 @@ batadv_hardif_neigh_create(struct batadv_hard_iface *hard_iface,
 	ether_addr_copy(hardif_neigh->addr, neigh_addr);
 	ether_addr_copy(hardif_neigh->orig, orig_node->orig);
 	hardif_neigh->if_incoming = hard_iface;
-	hardif_neigh->last_seen = jiffies;
+	WRITE_ONCE(hardif_neigh->last_seen, jiffies);
 
 	kref_init(&hardif_neigh->refcount);
 
-- 
2.47.3