[PATCH net-next 09/15] vxlan: Convert FDB garbage collection to RCU

[Ido Schimmel <idosch@nvidia.com>]

Instead of holding the FDB hash lock when traversing the FDB linked list
during garbage collection, use RCU and only acquire the lock for entries
that need to be removed (aged out).

Avoid races by using hlist_unhashed() to check that the entry has not
been removed from the list by another thread.

Note that vxlan_fdb_destroy() uses hlist_del_init_rcu() to remove an
entry from the list which should cause list_unhashed() to return true.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
 drivers/net/vxlan/vxlan_core.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index f9840a4b6e44..c3511a43ce99 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2819,14 +2819,13 @@ static void vxlan_cleanup(struct timer_list *t)
 {
 	struct vxlan_dev *vxlan = from_timer(vxlan, t, age_timer);
 	unsigned long next_timer = jiffies + FDB_AGE_INTERVAL;
-	struct hlist_node *n;
 	struct vxlan_fdb *f;
 
 	if (!netif_running(vxlan->dev))
 		return;
 
-	spin_lock(&vxlan->hash_lock);
-	hlist_for_each_entry_safe(f, n, &vxlan->fdb_list, fdb_node) {
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(f, &vxlan->fdb_list, fdb_node) {
 		unsigned long timeout;
 
 		if (f->state & (NUD_PERMANENT | NUD_NOARP))
@@ -2837,15 +2836,19 @@ static void vxlan_cleanup(struct timer_list *t)
 
 		timeout = READ_ONCE(f->updated) + vxlan->cfg.age_interval * HZ;
 		if (time_before_eq(timeout, jiffies)) {
-			netdev_dbg(vxlan->dev, "garbage collect %pM\n",
-				   f->eth_addr);
-			f->state = NUD_STALE;
-			vxlan_fdb_destroy(vxlan, f, true, true);
+			spin_lock(&vxlan->hash_lock);
+			if (!hlist_unhashed(&f->fdb_node)) {
+				netdev_dbg(vxlan->dev, "garbage collect %pM\n",
+					   f->eth_addr);
+				f->state = NUD_STALE;
+				vxlan_fdb_destroy(vxlan, f, true, true);
+			}
+			spin_unlock(&vxlan->hash_lock);
 		} else if (time_before(timeout, next_timer)) {
 			next_timer = timeout;
 		}
 	}
-	spin_unlock(&vxlan->hash_lock);
+	rcu_read_unlock();
 
 	mod_timer(&vxlan->age_timer, next_timer);
 }
-- 
2.49.0