[PATCH net-next 09/15] batman-adv: annotate originator last_seen with READ/WRITE_ONCE

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

The last_seen field for batadv_orig_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_ogm.c  | 7 ++++---
 net/batman-adv/originator.c | 8 +++++---
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 85e99506a53f5..ee3a5ac465012 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -1291,7 +1291,7 @@ static bool batadv_iv_ogm_calc_tq(struct batadv_orig_node *orig_node,
 	if (orig_node == orig_neigh_node)
 		neigh_node->last_seen = jiffies;
 
-	orig_node->last_seen = jiffies;
+	WRITE_ONCE(orig_node->last_seen, jiffies);
 
 	/* find packet count of corresponding one hop neighbor */
 	orig_eq_count = batadv_iv_orig_ifinfo_sum(orig_neigh_node, if_incoming);
@@ -2045,10 +2045,12 @@ batadv_iv_ogm_orig_dump_subentry(struct sk_buff *msg, u32 portid, u32 seq,
 				 bool best)
 {
 	unsigned int last_seen_msecs;
+	unsigned long last_seen;
 	void *hdr;
 	u8 tq_avg;
 
-	last_seen_msecs = jiffies_to_msecs(jiffies - orig_node->last_seen);
+	last_seen = READ_ONCE(orig_node->last_seen);
+	last_seen_msecs = jiffies_delta_to_msecs(jiffies - last_seen);
 
 	if (!batadv_iv_ogm_neigh_get_tq_avg(neigh_node, if_outgoing, &tq_avg))
 		return 0;
diff --git a/net/batman-adv/bat_v.c b/net/batman-adv/bat_v.c
index 4a25e513864ca..2679090c3368b 100644
--- a/net/batman-adv/bat_v.c
+++ b/net/batman-adv/bat_v.c
@@ -302,6 +302,7 @@ batadv_v_orig_dump_subentry(struct sk_buff *msg, u32 portid, u32 seq,
 {
 	struct batadv_neigh_ifinfo *n_ifinfo;
 	unsigned int last_seen_msecs;
+	unsigned long last_seen;
 	u32 throughput;
 	void *hdr;
 
@@ -313,7 +314,8 @@ batadv_v_orig_dump_subentry(struct sk_buff *msg, u32 portid, u32 seq,
 
 	batadv_neigh_ifinfo_put(n_ifinfo);
 
-	last_seen_msecs = jiffies_to_msecs(jiffies - orig_node->last_seen);
+	last_seen = READ_ONCE(orig_node->last_seen);
+	last_seen_msecs = jiffies_delta_to_msecs(jiffies - last_seen);
 
 	if (if_outgoing != BATADV_IF_DEFAULT &&
 	    if_outgoing != neigh_node->if_incoming)
diff --git a/net/batman-adv/bat_v_ogm.c b/net/batman-adv/bat_v_ogm.c
index 70846c997410d..03c70d91e64d1 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -626,6 +626,7 @@ static int batadv_v_ogm_metric_update(struct batadv_priv *bat_priv,
 	struct batadv_neigh_ifinfo *neigh_ifinfo = NULL;
 	struct batadv_orig_ifinfo *orig_ifinfo;
 	bool protection_started = false;
+	unsigned long last_seen;
 	u32 path_throughput;
 	int ret = -EINVAL;
 	s32 seq_diff;
@@ -656,9 +657,9 @@ static int batadv_v_ogm_metric_update(struct batadv_priv *bat_priv,
 	if (seq_diff < 0 && !protection_started)
 		goto out;
 
-	neigh_node->last_seen = jiffies;
-
-	orig_node->last_seen = jiffies;
+	last_seen = jiffies;
+	neigh_node->last_seen = last_seen;
+	WRITE_ONCE(orig_node->last_seen, last_seen);
 
 	orig_ifinfo->last_real_seqno = ntohl(ogm2->seqno);
 	orig_ifinfo->last_ttl = ogm2->ttl;
diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index f06583ef9b3f5..3b925ba9c9723 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -977,7 +977,7 @@ struct batadv_orig_node *batadv_orig_node_new(struct batadv_priv *bat_priv,
 	WRITE_ONCE(orig_node->last_ttvn, 0);
 	orig_node->tt_buff = NULL;
 	orig_node->tt_buff_len = 0;
-	orig_node->last_seen = jiffies;
+	WRITE_ONCE(orig_node->last_seen, jiffies);
 	reset_time = jiffies - 1 - msecs_to_jiffies(BATADV_RESET_PROTECTION_MS);
 	orig_node->bcast_seqno_reset = reset_time;
 
@@ -1210,16 +1210,18 @@ static bool batadv_purge_orig_node(struct batadv_priv *bat_priv,
 {
 	struct batadv_neigh_node *best_neigh_node;
 	struct batadv_hard_iface *hard_iface;
+	unsigned long last_seen;
 	struct list_head *iter;
 	bool changed_ifinfo;
 	bool changed_neigh;
 
-	if (batadv_has_timed_out(orig_node->last_seen,
+	last_seen = READ_ONCE(orig_node->last_seen);
+	if (batadv_has_timed_out(last_seen,
 				 2 * BATADV_PURGE_TIMEOUT)) {
 		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
 			   "Originator timeout: originator %pM, last_seen %u\n",
 			   orig_node->orig,
-			   jiffies_to_msecs(orig_node->last_seen));
+			   jiffies_to_msecs(last_seen));
 		return true;
 	}
 	changed_ifinfo = batadv_purge_orig_ifinfo(bat_priv, orig_node);
-- 
2.47.3